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Recent Aqueous Environments in Martian Impact Craters: An Astrobiological Perspective
Abstract
The discovery of gullies and debris aprons raises the question of the existence of aqueous environments on Mars in recent geological times and its astrobiological implications. Three cases of such environments are surveyed at MOC high resolution in the E-Gorgonum chaos and Newton and Hale craters. The regional setting of these craters suggests that the mechanisms of aquifer destabilization, flow discharge, and gully formation in these three cases result from local geological triggers that can include impact cratering, and tectonic processes, rather than climate or insolation factor. We take as a working hypothesis that microbial life appeared on Mars in ancient geological times, probably in a geothermal environment but potentially evolving via infrared detection systems to give photosynthetic communities under the selective pressure of energetic solar radiation. We hypothesize that some microbial communities could have survived underground in either dormant or active state, or that their biomolecules could be preserved either frozen or desiccated in the subsurface beneath the upper oxidized zone. We assess the known environmental constraints for life and what type of potential habitats are provided in these three craters by aquifer discharges using comparison with terrestrial analogues and their associated microbial communities. These environments include: (1) the release of water on a dry crater floor in E-Gorgonum and the possibility for microorganisms and preserved biomolecules to be flushed out and mixed in with the sediment exposed at the surface; (2) the evidence of a recent lacustrine episode in the Newton crater with analogy to Antarctic Dry Valley lakes; (3) the exposure on the floor of Hale crater of material from a regional subsurface that is likely to have retained traces of one of the oldest martian bodies of water recognized to date (Parker et al. 2000) in the Argyre basin. We show how the water in Argyre (∼3.8 billion years ago (Gya) was likely to have been alterated by hydrothermal processes and how the subsequent formation of the 150-km Hale crater on the northern ring of Argyre generated hydrothermal pumping. This accounts for the anomalously high location of the springs on the crater crests today with respect to the rest of the regional subsurface distribution. Finally, we envision current impact cratering as a factor for destabilizing aquifers on Mars today, thus creating new environments. We analyze the implications of impacts for two geological types of rock units that could harbor traces of life. As a result, we compare the potential of astrobiological exploration of crater floors, rims, and ejecta on future missions to Mars.
... Consequently, deterioration of outermost growth layers would provide access to water and oxygen molecules to get into the inner layers and later to the nuclei region. Recent studies have shown the potential implications of water (Cabrol et al., 2001) and oxygen (Shekhtman, 2019) availability in the Martian environment, which allows for the possibility of the survival of microbial communities in the subsurface beneath the oxidized zone. Evidence from various sources, Sudeera Wickramarathna et al. ...
... including Martian meteorites (Greenwood et al., 2000), imagery of large Amazonian palaeo lakes (Cabrol and Grin, 1999) and implications from an atmosphere evolution model (Haberle et al., 2000) and Viking mission findings (Cabrol et al., 2001) indicate the existence of hydrological activities on Martian environment. Furthermore, previous studies hypothesized that living organisms may have been trapped in the Martian regolith under dormant conditions (e.g. ...
... Furthermore, previous studies hypothesized that living organisms may have been trapped in the Martian regolith under dormant conditions (e.g. permafrost bacteria) and could reproduce seasonal or cyclical favourable conditions (Cabrol et al., 2001). A recent study conducted above the surface of Gale Crater on Mars showed significant seasonal and interannual fluctuations of oxygen suggesting an unknown atmospheric or surface mechanism related to oxygen formation (Trainer et al., 2019;Cabrol et al., 2001). ...
Previous exploration missions have revealed Mars as a potential candidate for the existence of extraterrestrial life. If life could have existed beneath the Martian subsurface, biosignatures would have been preserved in iron-rich minerals. Prior investigations of terrestrial biosignatures and metabolic processes of geological analogues would be beneficial for identifying past metabolic processes on Mars, particularly morphological and chemical signatures indicative of past life, where biological components could potentially be denatured following continued exposure to extreme conditions. The objective of the research was to find potential implications for Martian subsurface life by characterizing morphological, mineralogical and microbial signatures of hematite deposits, both hematite rock and related soil samples, collected from Highland Complex of Sri Lanka. Rock samples examined through scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectroscopy. Analysis showed globular and spherical growth layers nucleated by bacteria. EDX results showed a higher iron to oxygen ratio in nuclei colonies compared to growth layers, which indicated a compositional variation due to microbial interaction. X-ray diffraction analysis of the hematite samples revealed variations in chemical composition along the vertical soil profile, with the top surface soil layer being particularly enriched with Fe 2 O 3 , suggesting internal dissolution of hematite through weathering. Furthermore, inductively coupled plasma-mass spectrometry analyses carried out on both rock and soil samples showed a possible indication of microbially induced mineral-weathering, particularly release of trapped trace metals in the parent rock. Microbial diversity analysis using 16S rRNA gene sequencing revealed that the rock sample was dominated by Actinobacteria and Proteobacteria , specifically, members of iron-metabolizing bacterial genera, including Mycobacterium , Arthrobacter , Amycolatopsis , Nocardia and Pedomicrobium . These results suggest that morphological and biogeochemical clues derived from studying the role of bacterial activity in hematite weathering and precipitation processes can be implemented as potential comparative tools to interpret similar processes that could have occurred on early Mars.
... The Columbia Hills site ( Figure 2V) is within Gusev crater which lies at the downstream 643 terminus of Ma'adim Vallis. The floor of Gusev may have hosted lacustrine sediments, deposited 644 by water draining from Ma'adim Vallis ( Cabrol et al., 1996Cabrol et al., , 2001Cabrol and Grin 1999;Irwin 645 et al., 2002), but they are now largely buried by Hesperian-aged basalts ( Milam et al., 2003;646 Greeley et al., 2004;McSween et al., 2004;Golombek et al., 2006). The ROIs identified for the 647 landing site are "land on" and largely centered on hills embayed by the volcanic plains materials 648 informally named "Columbia Hills." ...
... The ROIs identified for the 647 landing site are "land on" and largely centered on hills embayed by the volcanic plains materials 648 informally named "Columbia Hills." Possible outcrops of unknown, but possible lacustrine and 649 (or) deltaic materials occur outside the ellipse to the south (e.g., Cabrol et al., 1996;2001;Cabrol 650 and Grin, 1999). 651 ...
The process of identifying the landing site for NASA's Mars 2020 rover began in 2013 by defining threshold mission science criteria related to seeking signs of ancient habitable conditions, searching for biosignatures of past microbial life, assembling a returnable cache of samples for possible future return to Earth, and collecting data for planning eventual human missions to the surface of Mars. Mission engineering constraints on elevation and latitude were used to identify candidate landing sites that addressed the scientific objectives of the mission. However, for the first time these constraints did not have a major influence on the viability of candidate sites and, with the new entry, descent, and landing capabilities included in the baseline mission, the vast majority of sites were evaluated and down-selected on the basis of science merit. More than 30 candidate sites with likely acceptable surface and atmospheric conditions were considered at a series of open workshops in the years leading up to the launch. During that period, iteration between engineering constraints and the evolving relative science potential of candidate sites led to the identification of three final candidate sites: Jezero crater (18.4386°N, 77.5031°E), northeast (NE) Syrtis (17.8899°N,77.1599°E) and Columbia Hills (14.5478°S, 175.6255°E). The final landing site will be selected by NASA's Associate Administrator for the Science Mission Directorate. This paper serves as a record of landing site selection activities related primarily to science, an inventory of the number and variety of sites proposed, and a summary of the science potential of the highest-ranking sites.
... Unambiguous, ground-based evidence of a range of past aqueous activity has been collected from Gale crater by the Mars Science Laboratory rover Curiosity since 2012 (e.g., [8,[10][11][12][13]). Thus, we chose this example to compare-and as necessary contrast-our analogue site. It must be noted that there is also ubiquitous evidence for similar systems elsewhere on Mars [14]. ...
... It formed during the late Noachian, creating impact melt, an ejecta blanket and a central uplift [15], all of which are currently covered by sediment and/or eroded. Before the arrival of the Curiosity rover, the crater had been extensively studied with remote data, including evidence for the existence of a fluvio-lacustrine system [10,14] the sedimentology of the central mount (e.g., [16]) and the occurrence of sulphate-, haematite-, and clay-bearing signatures in CRISM spectra [16,17]. ...
Evidence indicates that Gale crater on Mars harboured a fluvio-lacustrine environment that was subjected to physio-chemical variations such as changes in redox conditions and evaporation with salinity changes, over time. Microbial communities from terrestrial environmental analogues sites are important for studying such potential habitability environments on early Mars, especially in laboratory-based simulation experiments. Traditionally, such studies have predominantly focused on microorganisms from extreme terrestrial environments. These are applicable to a range of Martian environments; however, they lack relevance to the lacustrine systems. In this study, we characterise an anoxic inter-tidal zone as a terrestrial analogue for the Gale crater lake system according to its chemical and physical properties, and its microbiological community. The sub-surface inter-tidal environment of the River Dee estuary, United Kingdom (53°21′15.40″ N, 3°10′24.95″ W) was selected and compared with available data from Early Hesperian-time Gale crater, and temperature, redox, and pH were similar. Compared to subsurface ‘groundwater’-type fluids invoked for the Gale subsurface, salinity was higher at the River Dee site, which are more comparable to increases in salinity that likely occurred as the Gale crater lake evolved. Similarities in clay abundance indicated similar access to, specifically, the bio-essential elements Mg, Fe and K. The River Dee microbial community consisted of taxa that were known to have members that could utilise chemolithoautotrophic and chemoorganoheterotrophic metabolism and such a mixed metabolic capability would potentially have been feasible on Mars. Microorganisms isolated from the site were able to grow under environment conditions that, based on mineralogical data, were similar to that of the Gale crater’s aqueous environment at Yellowknife Bay. Thus, the results from this study suggest that the microbial community from an anoxic inter-tidal zone is a plausible terrestrial analogue for studying habitability of fluvio-lacustrine systems on early Mars, using laboratory-based simulation experiments.
... The rover, Zoë, is remotely operated by a science team under conditions simulated by a robotic mission to Mars. Building upon the technology employed by previous terrestrial rovers such as Rocky 7 [Arvidson et al., 1998], Nomad [Wettergreen et al., 1999;Cabrol et al., 2001aCabrol et al., , 2001b, FIDO [Arvidson et al., 2002], and Marsokhod [Stoker et al., 2001], Zoë has the capability to observe not only aspects of geology and climate [Wettergreen et al., 2005a[Wettergreen et al., , 2005b, but also to make direct observations of life [e.g., Weinstein et al., 2006]. The project's first two field seasons, 2003 and 2004, focused on technology demonstration, testing the robotics and integrating instrumentation and controls. ...
... (1) arid, low temperature desert conditions, (2) magma-water interactions and other hydrothermal activity, (3) evidence of tectonic processes, including fracturing, faulting, and basin formation, (4) presence of analogous materials, including igneous mineralogy and thick evaporite sequences, (5) structurally controlled basins and collapse-related depressions, (6) landscape features related to aqueous processes such as sapping channels and alluvial fans, (7) landscape features related to climate-driven aqueous processes such as floodcarved terrain and dry lakebeds [e.g., Mouginis-Mark, 1985, 1990Baker et al., 1991;Scott et al., 1993Scott et al., , 1995Tanaka et al., 1998Tanaka et al., , 2005Chong Diaz et al., 1999;Dohm et al., 2001aDohm et al., , 2001bDohm et al., , 2001cDohm et al., , 2004Cabrol et al., 2001bCabrol et al., , 2007Baker, 2001;Christensen et al., 2001;Fairén et al., 2003;Neukum et al., 2004;Márquez et al., 2004;Squyres et al., 2004;Gendrin et al., 2005;McSween et al., 2006;Warren-Rhodes et al., 2007a, 2007bSchultze-Makuch et al., 2007]. The specific study sites within the Atacama were chosen to represent a spectrum of habitability, generally constrained by relative abundance of liquid water delivered to putative near-surface habitats by fog, clouds, and potentially rain/ snowfall. ...
The science goals of the Life in the Atacama (LITA) robotic field
experiment are to understand habitat and seek out life in the Atacama
Desert, Chile, as an analog to future missions to Mars. To those ends,
we present a new data analysis tool, the LITA Data Scoring System (DSS),
which (1) integrates rover and orbital data relevant to environmental
habitability and life detection, and (2) provides a standard metric, or
``score'' to evaluate (a) the potential habitability, and (b) the
strength of evidence for life at all locales along the rover's traverse.
Designed and tested during the 2005 field campaign, first results from
the DSS indicate that the three selected sites in the Atacama Desert are
generally inhospitable. The strength of evidence for life is positively
correlated with potential habitability at two of the three sites. Using
factor analysis, we find three factors explain 79.9% of the variance in
biological observations and five factors explain 96.2% of the variance
in potential habitability across all sites. These factors are used to
focus a discussion of scoring variable definitions for future robotic
missions in the Atacama and of instrument selection and strategy
development for future robotic missions on Earth and Mars.
... The possible presence of gullies in several of the cratered landforms could also be further investigated as these are important in astrobiological research (e.g. Cabrol et al., 2001;Pablo and Fair en, 2004;Núñez et al., 2016;Pal, 2019). Subsurface radar investigations such as those carried out with the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) could clarify their origin through a detailed survey of the subsurface of these landforms. ...
This article presents a systematic morphological analysis of the topographic landforms at Olympia Undae and Scandia Cavi in the northern circumpolar region of Mars. The study has been performed using images from Mars Express and Mars Reconnaissance Orbiter, as well as topographic profiles from Mars Global Surveyor of 200 small and medium-size geological landforms (16 km diameter on average). The main morphometric parameters of these landforms have allowed their classification into three groups that include cratered structures, non-cratered structures, and complex irregular structures. In the cratered group, three subgroups can be distinguished: cratered cones, impact craters and undifferentiated craters. In turn, the non-cratered group includes two subgroups: peaked domes and simple domes. Their possible relation to internal, surface and impact processes is discussed.
... Such hydrothermal activity was proposed for martian impact melt sheets within crater walls (Newsom, 1980;Allen et al., 1982), hot springs bounding those melt sheets (Brakenridge et al., 1985), and in surrounding impact ejecta deposits SUEVITE GLASS HYDROGEN PRODUCTION 13 (Newsom et al., 1986). As on Earth, such sites on Mars are attractive astrobiological targets (e.g., Newsom et al., 2001;Cabrol et al., 2001). A series of thermal evolution models (e.g., Rathbun and Squyres, 2002;Abramov and Kring, 2005;Ivanov and Pierazzo, 2011;Abramov and Mojzsis, 2016) and chemical evolution models (e.g., Griffith and Shock, 1997;Kring, 2009, 2013;Schwenzer et al., 2012a; also reviewed by Osinski et al., 2013) were developed to explore those systems. ...
A sulfate-reducing population of thermophiles grew in porous, permeable niches within glass-bearing impact breccias of the Chicxulub impact crater. The microbial community grew in an impact-generated hydrothermal system that vented on the seafloor several hundred meters beneath the sea surface. Potential electron donors for that metabolism are hydrocarbons, although a strong C-isotope signature of that source does not exist. Model calculations explored here suggest that alteration of glass within the impact breccias may have produced H2 in sufficient quantities for population growth as the hydrothermal system cooled through thermophilic temperatures, although it is sensitive to the oxidation state of iron in the melt rock prior to hydrothermal alteration and the secondary mineral assemblage. At high water-to-rock ratios and temperatures below 45°C, H2 yields are insufficient to maintain a population of hydrogenotrophic sulfate-reducing bacteria, but yields double with a higher proportion of ferrous iron between 45 and 65°C. The most reduced rocks (i.e., highest proportion of ferrous iron) that are allowed to form andradite, which is observed in core samples, produce copious amounts of H2 in the temperature window for thermophiles and hyperthermophiles. Mixtures of melt rock and carbonate, which is observed in breccia matrices, produce somewhat less H2, and the onset of massive H2 production is shifted to higher temperatures (i.e., lower W/R).
... However, it cannot be excluded that IGHS existed in Martian impact craters, and it may well be that signals are simply too limited to be picked up through remote sensing. Furthermore, it is possible that any remains of life previously produced in hydrothermal systems in the crust (Fisk & Giovannoni, 1999;Jones et al., 2011;Michalski et al., 2013;Parnell et al., 2010) may be excavated and reactivated through an IGHS (Cabrol et al., 2001). ...
Hydrothermal systems provide a possible habitat for early life and are key targets in the quest for life outside Earth. In impact craters on Mars, hydrous minerals can represent products of impact‐generated hydrothermal systems (IGHS) or minerals already present in the crust and exposed during impact‐caused excavation. Because of its basaltic target rock, similar in composition to Martian crust, the Vista Alegre impact structure in Brazil is one of the very few analog structures that may reveal the origin of these minerals, if evidence of hydrothermal alteration is established. This work presents the results of a systematic search for evidence of hydrothermal alteration at the Vista Alegre impact structure. Four types of alteration were identified, all within a 2.5–3.0 km radius from the crater center: a zircon‐bearing melt veinlet, two sets of hydrothermal veins consisting predominantly of calcite and chabazite, and local alteration comprising saponite. Thermodynamic modeling suggests subsequent heating and cooling for each of the hydrothermal vein sets. Combined thermodynamic and spectrometric evidence indicates that development of a vigorous IGHS is unlikely. If similar processes occur on Mars, hydrous minerals are more likely preimpact phases exposed by excavation, rather than being formed through an IGHS.
... The possible presence of gullies in several of the cratered landforms could also be further investigated as these are important in astrobiological research (e.g. Cabrol et al., 2001;Pablo and Fair en, 2004;Núñez et al., 2016;Pal, 2019). Subsurface radar investigations such as those carried out with the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) could clarify their origin through a detailed survey of the subsurface of these landforms. ...
This article presents a systematic morphological analysis of the topographic landforms at Olympia Undae and Scandia Cavi in the northern circumpolar region of Mars. The study has been performed using images from Mars Express and Mars Reconnaissance Orbiter, as well as topographic profiles from Mars Global Surveyor of 200 small and medium-size geological landforms (16 km diameter on average). The main morphometric parameters of these landforms have allowed their classification into three groups that include cratered structures, non-cratered structures, and complex irregular structures. In the cratered group, three subgroups can be distinguished: cratered cones, impact craters and undifferentiated craters. In turn, the non-cratered group includes two subgroups: peaked domes and simple domes. Their possible relation to internal, surface and impact processes is discussed.
... This contrasts with DIR at circumneutral pH, where the majority of Fe(II) resides in the solid phase, as demonstrated in experiments and natural systems (e.g., Canfield et al., 1993), which significantly affects Fe isotope mass balance (Percak-Dennett et al., 2013). The applicability of Fe isotopes to search for microbial activity in low-pH environments could also be extended to non-Earth systems, such as extraterrestrial acidic systems (e.g., Martian paleoenvironments) where ferric (hydr)oxides were possibly abundant (Fernández-Remolar et al., 2005;Bibring et al., 2006;Morris et al., 2006;Hurowitz and McLennan, 2007;Morris et al., 2008;Hurowitz et al., 2010;Dauphas et al., 2012;Peretyazhko et al., 2018) to support mineral-based microbial metabolism (Boston et al., 1992;Horneck, 2000;Cabrol et al., 2001;Nixon et al., 2013). ...
Dissimilatory iron reduction (DIR) plays an essential role in biogeochemical Fe cycling in anoxic environments. At near-neutral pH, in both biotic and abiotic systems, aqueous Fe(II) (Fe(II)aq) interacts with reactive ferric (hydr)oxides via electron transfer and atom exchange that is catalyzed by large amounts of sorbed Fe(II). This may result in substantial Fe isotope exchange, which, at equilibrium, produces up to a ∼4‰ ⁵⁶Fe/⁵⁴Fe fractionation between coexisting oxide/hydroxide and Fe(II)aq, depending on mineralogy. The role of biology in such systems has been interpreted to lie in the production of Fe(II) rather than a specific “vital” effect, such as enzymatic and kinetic processes. Under acidic abiotic conditions, however, the lack of sorbed Fe(II) generates little Fe isotope exchange, and, by extension, it has been expected that little exchange would occur during DIR at low pH if sorbed Fe(II) is the key component for catalyzing isotopic exchange.
In this study, we explored the extent and mechanism of Fe isotope exchange between Fe(II)aq and ferric hydroxides (ferrihydrite and goethite), including determination of the ⁵⁶Fe/⁵⁴Fe fractionations during DIR by Acidianus strain DS80 at pH ∼ 3.0 and 80 °C, over 19 days of incubation. Significant Fe(III) reduction occurred for both minerals along with large changes in Fe isotope compositions for Fe(II)aq, indicating Fe isotope exchange. Solid-phase extractions using HCl confirmed a lack of sorbed Fe(II), which suggests that a mechanism other than sorption is required to catalyze Fe isotope exchange during DIR at low pH. Reactive Fe(III) (Fe(III)reac) extracted from the mineral surface allowed for the calculation of the Fe pools that underwent isotopic exchange. A total of ∼20% of goethite and ∼60% of ferrihydrite underwent isotopic exchange over 19 days. For goethite from biotic experiments, we calculate a Fe(III)reac-Fe(II)aq fractionation factor of 1.57 ± 0.52‰, which is larger than the abiotic equilibrium fractionation factor (∼0.73‰ at 80 °C). This result is consistent with previous work on DIR of goethite at neutral pH, where a fractionation factor larger than equilibrium was interpreted to reflect an isotopically distinct “distorted surface layer” of goethite produced during exchange with Fe(II)aq. In contrast to goethite, the difference between the Fe(III)reac-Fe(II)aq fractionation factor for ferrihydrite from our biotic reactors (2.91 ± 0.40‰) and the abiotic equilibrium fractionation factor (∼2.28‰ at 80 °C, under silica-free conditions) is smaller.
Ultimately, the contrast in the extent of Fe isotope exchange between biotic and abiotic experiments emphasizes the importance of biology in promoting Fe isotope exchange in acidic systems. We speculate that the unique role of biology at low pH in catalyzing Fe isotope exchange, not seen in equivalent abiotic systems, must lie in the transport of electrons to the ferric hydroxide surface that produces Fe(II) atoms in situ. This suggests that isotopic exchange occurs on an atom-by-atom basis as Fe(III) is reduced to Fe(II), followed by the release of Fe(II) into solution. This study demonstrates that significant variations in Fe isotope compositions may be uniquely produced in acidic environments where microbial Fe cycling occurs via DIR, compared to minor isotopic variations observed previously in acidic abiotic systems.
... Volcanic aquifers could have sustained long-term subsurface sheltered habitats against changing surface conditions after 4.1 Ga, with cycling of water, energy, and nutrients (e.g., Fairén et al., 2003;Schulze-Makuch et al., 2007), as well as transient subaerial habitats in hydrothermal springs, geysers, and pools (e.g., Walter and Des Marais, 1993;Cady and Farmer, 1996;Farmer, 1996;Walter, 1996;Gulick, 1998;Farmer and Des Marais, 1999;Cady et al., 2003;Allen and Oehler, 2008;Hofmann et al., 2008). Impact cratering produced an additional source of hydrothermal systems lasting up to tens of thousands of years for the largest impacts (e.g., Cabrol and Grin, 2001;Abramov and Kring, 2005;Newsom, 2010;Osinski and Pierazzo, 2012). On Earth, these environments are conducive to hypogene and supergene clay formation (e.g., Hazen et al., 2013). ...
Earth's biological and environmental evolution are intertwined and inseparable. This coevolution has become a fundamental concept in astrobiology and is key to the search for life beyond our planet. In the case of Mars, whether a coevolution took place is unknown, but analyzing the factors at play shows the uniqueness of each planetary experiment regardless of similarities. Early Earth and early Mars shared traits. However, biological processes on Mars, if any, would have had to proceed within the distinctive context of an irreversible atmospheric collapse, greater climate variability, and specific planetary characteristics. In that, Mars is an important test bed for comparing the effects of a unique set of spatiotemporal changes on an Earth-like, yet different, planet. Many questions remain unanswered about Mars' early environment. Nevertheless, existing data sets provide a foundation for an intellectual framework where notional coevolution models can be explored. In this framework, the focus is shifted from planetary-scale habitability to the prospect of habitats, microbial ecotones, pathways to biological dispersal, biomass repositories, and their meaning for exploration. Critically, as we search for biosignatures, this focus demonstrates the importance of starting to think of early Mars as a biosphere and vigorously integrating an ecosystem approach to landing site selection and exploration. Key Words: Astrobiology-Biosignatures-Coevolution of Earth and life-Mars. Astrobiology 18, xxx-xxx.
... For large, deep bodies of water, an assortment of geologic and geochemical evidence points toward the previous existence of wide oceans over the Martian northern lowlands. As summarized by Farién et al. (2003), these include: (1) the Martian dichotomy boundary between the southern highlands and the northern lowlands (Tanaka et al., 1992) that provides a topographically lower area in the plains for very deep water accumulation, (2) evidence of longwavelength undulations of shorelines around the putative ocean caused by stresses associated with polar wandering (Sotin et al., 2003;Fairén et al., 2003;Perron et al., 2007); (3) the outflow channels, which either terminate at the boundary (Parker et al., 1993) or fade into the northern plains (Ivanov and Head, 2001); (4) the low density of superposed impact craters in the northern plains relative to the densely cratered southern highlands (Barlow and Bradley, 1990); (5) extremely flat topography at the distal reaches of the outflow channel systems in the northern lowlands (Head et al., 1999); (6) the broad occurrence of wide age-ranging glaciers that are interpreted to be linked to magmatic-triggered flooding and associated short-lived (tens of thousands of years) environmental/climatic changes (Cabrol et al., 2001); and (7) the chemical signatures reported for the northern plains, including high abundances of S and Cl or the possible existence of sulphate minerals and chloride salts, making a putative andesite-rich component or weathered basalt the dominant material type in the lowlands (Wyatt and McSween, 2002;Bibring et al., 2006). ...
... For large, deep bodies of water, an assortment of geologic and geochemical evidence points toward the previous existence of wide oceans over the Martian northern lowlands. As summarized by Farién et al. (2003), these include: (1) the Martian dichotomy boundary between the southern highlands and the northern lowlands (Tanaka et al., 1992) that provides a topographically lower area in the plains for very deep water accumulation, (2) evidence of longwavelength undulations of shorelines around the putative ocean caused by stresses associated with polar wandering (Sotin et al., 2003;Fairén et al., 2003;Perron et al., 2007); (3) the outflow channels, which either terminate at the boundary (Parker et al., 1993) or fade into the northern plains (Ivanov and Head, 2001); (4) the low density of superposed impact craters in the northern plains relative to the densely cratered southern highlands (Barlow and Bradley, 1990); (5) extremely flat topography at the distal reaches of the outflow channel systems in the northern lowlands (Head et al., 1999); (6) the broad occurrence of wide age-ranging glaciers that are interpreted to be linked to magmatic-triggered flooding and associated short-lived (tens of thousands of years) environmental/climatic changes (Cabrol et al., 2001); and (7) the chemical signatures reported for the northern plains, including high abundances of S and Cl or the possible existence of sulphate minerals and chloride salts, making a putative andesite-rich component or weathered basalt the dominant material type in the lowlands (Wyatt and McSween, 2002;Bibring et al., 2006). ...
... Impact-induced hydrothermal systems are relatively common on the Earth and the development of similar systems on Mars has received particular attention as they could have hosted temporal oases for life (Cabrol et al., 2001). The formation and emplacement of impact melt and hot breccias following shock compression can provide sufficient thermal gradients to drive a hydrothermal system, provided H 2 O is available in the environment. ...
The 12-km-wide Vargeão impact structure was formed 123 Myr ago in the Paraná basaltic province (southern Brazil). At this time the province region had a dry climate, although a large brackish aquifer had been formed in the underlying sandstones. It is therefore one of the best terrestrial analogs for studying impact-related products on a dry Martian surface environment with preserved ice-rich ground. The basalts within the impact structure display cm-sized breccia veins filled with lithic clasts, glassy remnants, newly formed Fe-oxyhydroxides and secondary phases, such as calcite, phyllosilicates and, subordinately quartz and zeolite. The textural and mineralogical study of these phases demonstrate their hydrothermal origin. Although the very center of the structure has experienced the highest pressures and temperatures, the most developed hydrothermal changes are recognized in an inner collar surrounding the central depression. This inner collar is also the location of major modifications of the rock magnetic properties. These magnetic signatures are related to the distribution of impact-related faults and to the formation of new iron oxides. Geochemical modelling indicate that their formation required low water/rock ratios. Our observations therefore suggest that hydrothermal alteration took place following the perturbation of the aquifer by the impact, but evidence for hydrothermal circulation is limited in comparison with other impact-related hydrothermal systems. This situation may be explained by the presence of the acquifer below the heat source, such a setting being exceptional for the Earth, but common on Mars. However, the spectroscopic signatures in visible/near infrared images suggest that this kind of impact-related hydrothermal alteration may be still indentified in large impact craters on Mars by orbital instruments. These results does not exlcude the possibility that more developed alteration took place in breccias that are today eroded.
... As argued in the discussions of the previous questions, there is considerable evidence that surface water was abundant on early Mars. Potential sources that may have contributed to aqueous alteration include the early atmosphere; drainage systems, lakes, and other large standing bodies of water (Baker et al., 1991;Newsom et al., 1996;Cabrol et al., 2001;Clifford and Parker, 2001); and the likely presence of shallow and deep aquifers (Clifford, 1993;Forsberg-Taylor et al., 2004). ...
The influx of new data received from recent spacecraft missions, the study of Martian meteorites, recent progress in early climate modeling, the growing evidence for abundant water on early Mars, and the rapid pace of new discoveries about the origin and diversity of life on Earth have reinvigorated interest in both the conditions that prevailed on Mars during its first ∼1.5 billion years of geologic history and their potential implications for the development of life. These issues were initially discussed at the First Early Mars Conference, which was held in Houston, Texas, in April 1997 and then again at the Second Early Mars Conference, which was held in Jackson Hole, Wyoming, in October 2004. The scientific content of these meetings was captured in the meeting abstracts, Key Questions (identified by the meeting participants and reported to the Mars Exploration Program Analysis Group, MEPAG), and two associated Special Sections of JGR-Planets, which were published in December 1998 (with 12 papers) and December 2005 (with 25 papers). On 2125 May 2012, about 100 scientists gathered at the Hyatt Regency Hotel in Lake Tahoe, Nevada to participate in the Third International Conference on Early Mars: Geologic and Hydrologic Evolution, Physical and Chemical Environments, and the Implications for Life. Like its predecessors, the Third Early Mars Conference brought together scientists from fields as diverse as planetary geology, atmospheres, climate, meteoritics, microbiology, and molecular biochemistry, to discuss the conditions that prevailed on the early Earth and Mars during their first ∼1.5 billion years of geologic history. Indeed, the study of early Mars is likely to provide critical insight into understanding the nature of the early Earth-for as much as 40% of the Martian surface is believed to date back to a period from which little survives in the Earths geologic record [Tanaka, 1986].
... Besides the underground activity, impact craters create topographic lows in a planet's surface, and so readily develop crater lakes by flow of surface and/or groundwater (Newsom et al., 1996;Cabrol et al., 2001;Newsom, 2010). In a crater like Gale, the water of an early crater lake would be heated significantly by the impact melt sheet and the shockheated and uplifted basement (McKay and Davis, 1991;Newsom et al., 1996). ...
Gale Crater, the landing site of the 2011 Mars Science Laboratory
mission, formed in the Late Noachian. It is a 150 km diameter complex
impact structure with a central mound (Mount Sharp), the original
features of which may be transitional between a central peak and peak
ring impact structure. The impact might have melted portions of the
substrate to a maximum depth of ˜17 km and produced a minimum of
3600 km3 of impact melt, half of which likely remained within
the crater. The bulk of this impact melt would have pooled in an annular
depression surrounding the central uplift, creating an impact melt pool
as thick as 0.5-1 km. The ejecta blanket surrounding Gale may have been
as thick as ˜600 m, which has implications for the amount of
erosion that has occurred since Gale Crater formed. After the impact, a
hydrothermal system may have been active for several hundred thousand
years and a crater lake with associated sediments is likely to have
formed. The hydrothermal system, and associated lakes and springs,
likely caused mineral alteration and precipitation. In the presence of
S-rich host rocks, the alteration phases are modelled to contain sheet
silicates, quartz, sulphates, and sulphides. Modelled alteration
assemblages may be more complex if groundwater interaction persisted
after initial alteration. The warm-water environment might have provided
conditions supportive of life. Deep fractures would have allowed for
hydraulic connectivity into the deep subsurface, where biotic chemistry
(and possibly other evidence of life) may be preserved.
... Impact-induced hydrothermal systems are relatively common on the Earth and the development of similar systems on Mars has received particular attention as they could have hosted temporal oases for life (Cabrol et al., 2001). The formation and emplacement of impact melt and hot breccias following shock compression can provide sufficient thermal gradients to drive a hydrothermal system, provided H 2 O is available in the environment. ...
... [14] Channels have also been reported in the vicinity of the youthful (Late Hesperian/Early Amazonian [Cabrol et al., 2001]) 140 km-diameter Hale Crater [Tornabene et al., 2008;Edgett et al., 2008, Philippoff et al., 2009. Some channels cut the Hale ejecta blanket, while others appear to originate at or beyond the ejecta margins. ...
Channels originating at or near the margins of the continuous ejecta blanket of the youthful (Late Hesperian/Early Amazonian) 140 km-diameter Hale Crater have previously been attributed to melting of ice in the target material by superheated impact melt or remobilization of saturated ejecta. However, the presence of channels in the vicinity of Hale that do not originate on or at the margins of the ejecta blanket but are similar in morphology to those that do may suggest that channel formation at Hale was triggered by seismic energy from the impact. A key example lies at 33.0°S, 39.7°W, ~250 km northwest of Hale, where a small scabland (e.g. morphologies similar to the Channeled Scabland of the Columbia River Plateau, Washington) is observed. The scabland is located too far from the Hale impact to be explained by thermal melting of subsurface ice during the impact event. The channels are not associated with the Hale ejecta blanket, and are therefore not related to dewatering processes. The channels appear to be geologically young, with few superposed craters. Distinct depositional facies are observed; the channels terminate in a topographic depression in which the channel deposits have ponded. These deposits also have very few superposed craters. Aeolian bedforms are observed atop the deposits, potentially a lag of coarse-grained sand from within the deposits. These bedforms are confined to the deposit surface and are not observed elsewhere in the area. We propose that this ``mini-scabland'' was formed by the release of shallow groundwater due to seismic energy from the Hale impact. Seismic energy from earthquakes can lead to groundwater release via ejection of confined groundwater and/or upwelling of an unconfined shallow water table. In the former case, the water is confined by an impermeable layer and is typically released by jetting or spouting, resulting in fissures and/or mounds referred to as mud volcanoes. The latter case produces widespread non-eruptive water-sediment flows due to a rising water table and soil liquefaction. Evidence for liquefaction associated with terrestrial impact events has been documented. Seismic energy can trigger groundwater flow at great distances; the 1964 Great Alaskan Earthquake triggered the ejection of water-saturated sediments > 400 km from the epicenter. The lack of fissures and cones in the vicinity of the mini-scabland suggests that water was released non-explosively, implying that the groundwater involved in carving the channels was likely very shallow in the subsurface and was unconfined. The presence of groundwater in the area of Hale at various times in martian history is suggested by the occurrence of a number of gullies---hypothesized to have formed from discharges from shallow aquifers---within Hale and in surrounding craters and nearby Nirgal Vallis, which appears to have formed due to groundwater sapping based on its morphology. The channels at Hale may hence give credence to the shallow aquifer model for martian gully formation.
... For large, deep bodies of water, an assortment of geologic and geochemical evidence points toward the previous existence of wide oceans over the Martian northern lowlands. As summarized by Farién et al. (2003), these include: (1) the Martian dichotomy boundary between the southern highlands and the northern lowlands (Tanaka et al., 1992) that provides a topographically lower area in the plains for very deep water accumulation, (2) evidence of longwavelength undulations of shorelines around the putative ocean caused by stresses associated with polar wandering (Sotin et al., 2003;Fairén et al., 2003;Perron et al., 2007); (3) the outflow channels, which either terminate at the boundary (Parker et al., 1993) or fade into the northern plains (Ivanov and Head, 2001); (4) the low density of superposed impact craters in the northern plains relative to the densely cratered southern highlands (Barlow and Bradley, 1990); (5) extremely flat topography at the distal reaches of the outflow channel systems in the northern lowlands (Head et al., 1999); (6) the broad occurrence of wide age-ranging glaciers that are interpreted to be linked to magmatic-triggered flooding and associated short-lived (tens of thousands of years) environmental/climatic changes (Cabrol et al., 2001); and (7) the chemical signatures reported for the northern plains, including high abundances of S and Cl or the possible existence of sulphate minerals and chloride salts, making a putative andesite-rich component or weathered basalt the dominant material type in the lowlands (Wyatt and McSween, 2002;Bibring et al., 2006). ...
Abstract
A theory of how life emerges is couched in the context of the gravitational differentiation of terraqueous worlds massive enough to have held a carbon dioxide and nitrogen atmosphere. On the early Earth the differentiation to the various spheres—core, mantle, asthenosphere, lithosphere, hydrosphere and atmosphere—was largely a response to radiogenic and gravitational heat production in the interior. An effect of these density differentiations was to gather electrons in the core in native iron (Fe0 with its full compliment). However, early core formation still left the upper mantle relatively electron-rich (in FeII-bearing minerals), compared to the exhaling and accreting oxidized volatiles (H2O, CO2, N2, NO, SO2, P4O10) that composed the early hydrosphere and atmosphere. The atoms comprising these oxidized molecules are forced to share electrons covalently, rendering some of them potential ̳electron acceptors‘. Hydrothermal H2 acted as the carrier gas of electrons derived from the reduced iron in the crust. Reductions (hydrogenations), particularly of marine CO2, NO (or NO3 -) and FeIII at alkaline submarine hydrothermal springs, led to the emergence of metabolic pathways, first in inorganic compartments, then in prokaryotic cells that multiplied exponentially to produce the early biosphere, the last sphere to differentiate (cf., Takai et al., 2004). At the larger scale of the solar system the volatiles differentiate from the sun outwards in response to the solar wind, radiation, the decline in the gravity field and condensation and sublimation. But again, the same tensions between the CO2-bearing waters and hydrothermal H2 would tend to drive life into being on other rocky terraqueous globes like Mars and perhaps on Europa and Enceladus (Russell and Hall, 1999; Vance et al., 2007). Without this geochemical potential there would and will be no life, for life is not the convergence of a myriad of organic molecules but a resolution of redox and pH tensions in an aqueous environment whereby simple organic molecules are first synthesized from CO2 and other minor entities before being polymerized, interacted with and even hydrolyzed. The unambiguous effluents from early cells would be acetate or acetic acid and its derivatives. Beyond the solar system the same logic applies. Only those extra solar planets with rocky interiors and hosting surface or ground waters containing dissolved carbon dioxide (dosed with nitric oxide) will have an accompanying biosphere, one that would be forced to emerge to resolve these same geochemical and electrochemical tensions.
... spe384-26 page 10 of 15 CONCLUSIONS Impact-related hydrothermal systems generated under large Martian craters are considered sites favorable for the origin and/or development of early life Cabrol et al., 2001). While sophisticated computer codes are available to model the evolution of a hydrothermal system (e.g., HYDRO-THERM; Hayba and Ingebritsen, 1994), the characterization of the initial conditions for modeling the onset of a hydrothermal system is still based on general scaling relationships (Daubar and Kring, 2001;Thorsos et al., 2001;2002). ...
Mars is the first place to look for any sign of present or past extraterrestrial life. Its surface shows many features indicative of the presence of surface and sub-surface water, while impact cratering and volcanism have provided temporary and local surface heat sources throughout Mars geologic history. In particular, impact-generated hydrothermal systems could have been some of the most favorable sites for the origin of life on Mars. We present initial results of hydrocode simulations of impacts on Mars aimed at characterizing the initial conditions required for modeling the onset and evolution of a hydrothermal system on the red planet. High-resolution 3D SOVA simulations of the early stages of impact cratering indicate that the amount of melt generated in impacts is sensitive to the impact velocity. In particular, cometary impacts produce 2 to 3 times more melting than asteroidal impacts for roughly the same final crater. The particular distribution of ice in the target (mixed cells versus layering) does not appear to significantly affect the overall shock decay. However, the description of the mixed material target, mixed cells of individual materials (basalt/ice) versus mixed material equation of state, may affect the overall results and requires a more detailed investigation, both theoretical and experimental. Modeling crater collapse is a necessary step to determine the final thermal state of the target underneath. Crater collapse simulations carried out with SALEB show that the combination of shock/plastic heating and the structural uplift of initially deeper strata create a water-bearing zone at depths where water is in the liquid stability field. In the central uplift, the high temperatures cause water to evaporate (steam-driven circulation). The simulations indicate that for a mid-sized crater (rim diameter around 30 km) the hydrothermal circulation is probably restricted to a ``column'' contained well within the final crater.
During the last six decades of planetary exploration, rapid developments in technology have helped enable the exploration of Mars. To demonstrate the technical feasibility of off-Earth mining, new technologies are being developed to identify, remotely extract, and collect commodities under different environmental conditions. Impressive machines, tools, and operational procedures have been developed that allow scientists to study in detail the atmosphere, surface, and subsurface of Mars, progressing from flybys to orbiters to stationary landers to rovers. Key technologies have been developed to provide data for understanding and characterizing the geology, mineralogy, internal structure, atmospheric composition, and dynamics, as well as to identify the possibility of life on Mars. This makes Mars a major target for human colonization, exploration, and mining.
The McMurdo Dry Valleys form the largest relatively ice-free area on the Antarctic continent. The perennially ice-covered lakes, ephemeral streams and extensive areas of exposed soil are subject to low temperatures, limited precipitation and salt accumulation. The dry valleys thus represent a region where life approaches its environmental limits. This unique ecosystem has been studied for several decades as an analog to environments on other planets, particularly Mars. For the first time, the detailed terrestrial research of the dry valleys is brought together here, presented from an astrobiological perspective. Chapters include a discussion on the history of research in the valleys, a geological background of the valleys, setting them up as analogs for Mars, followed by chapters on the various sub-environments in the valleys such as lakes, glaciers and soils. Includes concluding chapters on biodiversity and other analog environments on Earth.
Abstract—Over the course of the last 20 years, planetary exploration mission architectures have evolved from single-craft paradigms totally commanded from Earth, towards an adaptive multi-tier, multi-agent paradigm approximating full in-situ operational autonomy: Tier-Scalable Reconnaissance (TSR). The early beginnings of the TSR mission paradigm date back to 2001, in large part based on the realization that an integrated perspective from multiple vantages optimizes exploration and scientific return for the best possible scientific understanding. The notion of an overhead perspective when exploring planetary field sites was filed as a New Technology Report at JPL in May 2003, followed by the filing of three Caltech patents in 2003, 2005, and 2006, capturing the entire intrinsic nature of TSR. Moreover, the TSR paradigm was recognized by NASA with a NASA Board Space Act Award in 2009, and has been widely publicized and showcased in numerous public media over the years. This paper highlights several key elements of multi-tier and multi-agent planetary exploration mission architectures envisioned in the three originating Caltech patents. It also showcases past, present, and future missions with elements of the TSR paradigm, with the nearest to the full implementation of the paradigm thus far being the first autonomous flight of the Mars helicopter Ingenuity on April 19, 2021, which added an overhead perspective and guidance for a rover for the first time in the history of space exploration. TSR is fundamentally changing how planetary surface exploration is being conducted, and will optimize exploration and science return.
NASA's main scientific reason for exploring Mars is to determine the early evolution and the possibility of life on the red planet. Scientists have adopted an approach for identifying habitable environments on Mars that could be conducive to the early development and preservation of life (e.g., robotically exploring hydrothermal and lake deposits in impact basins). We believe the best approach in the search for life on Mars is to investigate the ancient terrains that exhibit sedimentological records comprising rock materials deposited during a time when Mars was more geologically and hydrologically active. A paradigm shift from investigating middle age (<3.7 Ga) resurfaced Martian environments to exploring the extremely ancient (>3.9 Ga) terrains is proposed here. Terra Cimmeria, Terra Sirenum, and Arabia Terra are all distinctly older terrains that have not been modified by the formation of the giant four impact basins (i.e., Hellas, Isidis, Argyre, and Chryse) and formed during a time when Mars contained a thicker atmosphere and operating dynamo/magnetic field. Exploring these ancient terrains will not only provide the best opportunity to inform on the earliest stage of Mars' evolution but also the early Earth and solar system.
Life is known to adapt in accordance with its surrounding environment and sustainable resources available to it. Since harsh conditions would have precluded any possible aerobic evolution of life at the martian surface, it is plausible that martian life, should it exist, would have evolved in such a way as to derive energy from more optimum resources. Iron is one of the most abundant elements present in the martian crust and occurs at about twice the amount present on Earth. Clay minerals contribute to about half the iron found in soils and sediments. On Earth, clay acts as an electron donor as well as an acceptor in the carbon cycles and thereby supports a wide variety of metabolic reactions. In this context, we consider the potential of Fe/Mg smectites, one of the most widely reported hydrated minerals on Mars, for preservation of macro- and microscopic biosignatures. We proceed by understanding the environmental conditions during the formation of smectites and various microbes and metabolic processes associated with them as indicated in Earth-based studies. We also explore the possibility of biosignatures and their identification within the Mars 2020 landing site (Jezero Crater) by using the astrobiological payloads on board the Perseverance rover.
While dynamical models indicate that both cometary and asteroid collisions likely contribute to the population of bodies that impact the inner solar system, the distinction between the craters produced by the two populations remains uncertain. Although cometary impacts larger than 10 km in diameter are rare, dynamical studies cannot confidently eliminate their possible contribution to the total impact population at levels lower than ~10%. Due to the speed and volatile content of comets, their impact should couple more energy with a planetary atmosphere and result in observable signatures. The tenuous atmosphere of Mars makes the planet an ideal location to recognize such signatures. Here we use computational simulations and laboratory experiments to model both asteroid and cometary impacts on Mars. We explore the relationship between such impacts and enigmatic radial streaks that form around certain impact craters due to high-speed, long-duration winds. While lower speed asteroid impacts into thick (500 m) surface ices also can produce intense outward winds, the global distribution of craters with impact-generated wind streaks limits this mode of origin to just a few candidates; the rest are likely cometary. Based on the occurrence and relatively young age of these craters, we conclude that ~1% of the impactors on Mars over the last 2 Ga resulted from Long-Period cometary impacts, which should be about 6 times higher on Earth. Inclusion of Jupiter-Family and Haley-type comets (but not including cometary asteroids) then predicts that ~ 16% of all terrestrial impacts, with important implications for future impact hazards on Earth.
Uzboi Vallis in northwestern Noachis Terra is the uppermost segment of the Noachian to Hesperian Uzboi-Ladon-Morava mesoscale outflow system that dominates regional northward drainage through Noachis and Margaritifer Terrae. Recently acquired High Resolution Imaging Science Experiment (HiRISE) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data, as well as topography, help to characterize the nature and origin of a previously unrecognized deposit on the floor of Uzboi Vallis at the confluence of Nirgal Vallis. The Uzboi floor deposit consists of a lower unit (~255 km³) and an upper unit (~34 km³). The origin and age of the lower unit are less constrained; it may have formed by a combination of impact (e.g., ejecta from Luki crater), fluvial/alluvial, and (or) mass wasting processes. The superimposed upper unit is symmetrical relative to the mouth of Nirgal, fan-shaped in planform and layered. The morphology and location of the upper unit are consistent with alluvial (and possibly debris flow) deposition related to discharge from Nirgal Vallis. Crater Luki and the upper unit likely postdate the draining of the short-lived lake in Uzboi that formed after the mid- to Late Hesperian Holden crater blocked the northern end of Uzboi. Late-stage aqueous activity from Nirgal may have been sustained to some extent by groundwater discharge from aquifers along Nirgal that were recharged when Uzboi hosted a lake and (or) somewhat limited precipitation-fed surface runoff. The associated climate in the mid- to Late Hesperian was favorable for such aqueous processes, and it may have provided habitable surface conditions in this region relatively late in Martian history.
Hale crater formed in the Early to Middle Amazonian and is one of the best preserved large craters on Mars. We focus on the emplacement of previously mapped distal continuous ejecta and newly recognized discontinuous distal ejecta deposits reaching up to 450?km northeast of Hale. The distal continuous ejecta deposits are typically tens of meters thick, likely water-rich, and subsequent dewatering of some resulted in flow along gradients of 10?m?km-1 for distances of tens of kilometers. The discontinuous distal ejecta are typically <10?m thick with volumes generally <0.5?km3 and embay Hale secondaries, which occur up to ~600?km from Hale. Both continuous and discontinuous distal ejecta deposits are typically smooth at scales of tens to hundreds of meters, relatively dark-toned, devoid of eolian bedforms, inferred to be mostly fine-grained, and were likely emplaced within hours to 1?2?days after impact. The occurrence of well-preserved discontinuous distal ejecta at Hale is unusual compared to other large Martian craters and could be due to impact into an ice-rich substrate that enabled their formation and (or) their survival after minimal postimpact degradation relative to older craters. The pristine nature of distal continuous and discontinuous distal deposits at Hale and the preservation of associated secondaries imply (1) low erosion rates after the Hale impact, comparable to those estimated elsewhere during the Amazonian; (2) the impact did not significantly influence long-term global or regional scale geomorphic activity or climate; and (3) the Hale impact occurred after late alluvial fan activity in Margaritifer Terra.
This chapter discusses the morphological, geological, and mineralogical features of lakes on Mars. The existence of lakes on ancient Mars is now widely accepted, but that was not always the case. The history of science shows that knowledge on any scientific question is shaped by the means of exploration and those means are molded by what we think the world is. Prior to MGS of the late 1990s, the relatively low resolution of orbital imagery made it difficult to confirm Martian paleolakes by direct observations, though their existence was inferred because valley networks had already been identified on Viking and Mariner 9 images. Whether the early climate of Mars was much warmer and wetter in the Noachian compared to the later geological epochs is still the subject of ongoing debate. The existence of standing bodies of water on Mars required that at some point in its history, possibly repeatedly, physicochemical and environmental conditions allowing water to circulate and to pond were met. In addition to mineralogy and morphology, another clue about the conditions at the time of lake formation can be revealed by numbers. At Viking resolution, 179 putative impact crater lakes were identified and 210 open lake systems were cataloged from a global survey using the most recent datasets. Combined, the results from morphology, mineralogy, and estimation of lake production support the idea that favorable conditions did exist on Mars to produce a few large bodies of water, and many more, smaller lakes that formed by processes analogous to those occurring on Earth.
SynonymsBreached crater; Breached-rim craterDefinitionA fluid-incised gap in a crater rimDescriptionIncisions through crater rims carved by inflows or outflows of water or lava. Crater rim cross-sections and breaches formed by outflowing fluid are often shaped like earthen-dam counterparts, i.e., the crater rim is triangular in cross section and the breach is trapezoidal (Wahl 1998; Coleman and Dinwiddie 2007).Subtypes(1)Inlet/inflow/entrance crater breach, inlet channel (Fig. 1): The majority of Martian crater breaches are broadly of this type, although several genetic types are encompassed in the category, including breaches by single head-cut channels; breaches by headward extension of channel or valley networks (Irwin et al. 2005), through crater rims, the breaches themselves often incised by dendritic channel networks; rim breaching by lateral migration of adjacent channels (e.g., Enns et al. 2010); and breaches cut by overtopping flows from surrounding fluid-filled plains (e.g., ...
This work investigates new insight into the relationship between
morphology and elevation of Martian valleys termini and hypothetical
Martian ocean including their implication for global climate change
using 128 pixels per degree MOLA data.
The morphology of delta deposits in crater lakes on Mars is indicative
of upstream (e.g., flow discharge and sediment properties) and
downstream (e.g., basin characteristics) parameters, from which the
hydrological conditions at the time of formation can be inferred. To
investigate the influences of these parameters on delta morphology, we
experimentally created deltas in crater-shaped basins by feeding a range
of constant flow discharges over a feeder channel of various sand
textures. We reproduced three categorically different types of deltas
including most of the types that have been identified on Mars. Our most
striking observation is that water level behavior (itself a unique
function of flow discharge, basin size and hypsometry, and basin floor
permeability) can explain most delta morphologies observed on Mars.
Stepped, retrograding deltas formed during water level rise, prograding
deltas formed during water level still stand, and during water level
fall deltas were partially destroyed by erosion. On Mars numerous
retrograding and prograding deltas were preserved, most of them without
indications of channel incisions or other fluvial modification. We
conclude that the main difference between a single-foreset prograding
delta and a multiple-foreset retrograding delta is the behavior of the
water level in the basin. These simple delta morphologies cannot be
reconciled with long-duration hydrological activity, because that would
imply crater lake fluctuations due to inherent complex water level
histories along with complex sediment delivery histories. Our
experiments and numerical verifications demonstrate that such deltas
preferentially form during one aqueous event, which parsimoniously
argues for short-duration hydrological activity.
This chapter examines the potential heat sources for Martian lakes, the implications of sedimentary and associated hydrothermal deposits for determining the history of climate on Mars, and for the search for deposits containing evidence of microbial habitability. The sedimentary deposits in lakes are important for studying the nature of habitable environments for microbial life on Mars and represent high-priority landing sites for future rover missions, such as MSL. Geomorphic evidence for the past existence of liquid water lakes on Mars and their associated sedimentary deposits continues to grow. The primary heat sources in large impact craters on Mars after their formation are, impact melts primarily generated by the shock wave, heat deposited in the basement below the transient cavity from passage of the shock wave, and additional heat in the central uplift from the uplifted geothermal gradient. Large volcanic centers on Mars such as Tharsis and Elysium likely produced long-lived hydrothermal systems that would have had a major effect on driving groundwater circulation in the surrounding regions and possibly producing lakes and possibly oceans. Essentially all lakes that could occur on Mars can be heated by solar energy or the heat flow from the typical geothermal gradient, but these sources of energy are small. Heated lakes may represent ideal sites to search for evidence of biotic or prebiotic organic processes on Mars.
This chapter examines the physiographic controls of planet-wide drainage and storage of water on the surface as lakes and ponds. Hydrogeomorphologic provinces are described as regional watersheds defined by topographic divides and terminal basins or low-elevation outlets. Sparse dendritic drainage patterns viewed on Mariner 9 and Viking Orbiter images provided some evidence of possible rainfall on the surface of Mars, but many investigators of that time preferred groundwater sources for most of the channels. Vast catastrophic outflows would fill a northern ocean and support a brief period of wet Mars with a hydraulic cycle including the growth of glaciers and rainfall. As the possibility of a wetter Mars grows, so does the possibility of extensive glacial action. As another possible mechanism for significant water at the surface, periodic climate change is proposed as a consequence of periodic shifts of Mars obliquity. A groundwater source, either by groundwater effluence or thawing of permafrost, is evidenced by large outflow channels associated by chaotic terrain. The chaos is created by the withdrawal of large amounts of groundwater and the subsequent collapse of the overlying terrain. Compaction by the weight of overlying sediment in depositional centers or emplacement of volcanic material on saturated regolith may be expected to produce a pressure drive to force connate water to the surface as seeps and springs around the edge of sedimentary basins.
The Mathematical Statistics Theory (MST) and the Mathematical Theory of Stochastic Processes (MTSP) are different branches of the more general Mathematical Probability Theory (MPT) that represents different aspects of some physical processes we can analyze using mathematics. Each model of a stochastic process according to the MTSP can provide one or more interpretations in the MST domain. The importance of MTSP is that each such interpretation can provide large amount of new information. While large body of work on the impact crater statistics according to MST has already been done, it is yet to be investigated as to how we can model a stochastic process according to MTSP; for example, bombardment of the planetary surface or something else in a Lunar and Planetary Science (LPS) domain. In order to show possible achievements, the possible existence of a Martian ocean was chosen as a query that could be addressed through computations using presumptions according to MTSP, including probability of existence as well as lateral and vertical extent and duration of time. While the presumptions for this particular case will also be addressed in certain degree, this will be done primarily to show complexities of some physical process that can be modeled, rather than to prove correctness of the concrete values computed here. While this in itself can be the objective in some future work toward the formal proof of the probability, extent, and timing of oceans on Mars, the basic idea here is to show the basic principles of MTSP, and its potential for addressing LPS-related phenomena. Here, I attempt to show how this approach can: (1) provide large amounts of previously unknown information about physical processes on the surface of the planet, (2) lead to a better understanding of the processes that have shaped the surface of the planet, and/or (3) help constrain the amount of resurfacing. Coupled with other current methodologies, MTSP can result in a better understanding of the history of Mars, as well as other lunar and planetary bodies.
The morphometry and occurrence of crater-bound fans in southern Margaritifer Terra that were active from around the Hesperian–Amazonian boundary into the Early Amazonian is consistent with emplacement related to synoptic precipitation. Precipitation, possibly occurring as snow, may have been locally influenced by topography and (or) orbital variations. It is not known how much of the total sediment inventory in the fans relates to this late activity versus possible earlier events where water may have been available from alternate sources such as impact-related melting of ground ice. Winds may have concentrated late occurring precipitation into existing relief and (or) preexisting alcoves that facilitated physical weathering to produce fine sediments later incorporated into fans. Two of the craters containing fan deposits, Holden and Eberswalde, were finalists for the MSL landing site. Results suggest that exposed and accessible fan sediments at both crater sites may record a late period of colder, drier conditions relative to early Mars that was punctuated by ephemeral water-driven activity.
A two-plus year process of identifying and evaluating landing sites for the NASA 2003 Mars Exploration Rovers began with definition of mission science objectives, preliminary engineering requirements, and identification of ∼155 potential sites in near-equator locations (these included multiple ellipses for locations accessible by both rovers). Four open workshops were used together with ongoing engineering evaluations to narrow the list of sites to four: Meridiani Planum and Gusev Crater were ranked highest for science, with southern Isidis Basin and a “wind safe” site in Elysium following in order. Based on exhaustive community assessment, these sites comprise the best-studied locales on Mars and should possess attributes enabling mission success.
The new GT-115225 catalogue of martian craters was analyzed using 1/128° MOLA data and Topography-Profile Diagrams (TPDs). The results are newly discovered differences in distribution between shallow and deep and between large and small craters.
The association of channels, inner terraces, and delta-like features with Martian impact craters has previously been interpreted as evidence in favor of the past existence of crater lakes on Mars. However, examination of a candidate crater-lake system in western Memnonia suggests instead that its features may have formed through igneous processes involving the flow and ponding of lava. Accumulations of material in craters and other topographic lows throughout much of the study region have characteristics consistent with those of volcanic deposits, and terraces found along the inner flanks of some of these craters are interpreted as having formed through drainage or subsidence of volcanic materials. Channels previously identified as inlets and outlets of the crater-lake system are interpreted instead as volcanic rilles. These results challenge previous interpretations of terrace and channel features in the study region and suggest that candidate crater lakes located elsewhere should be reexamined.
Crater statistics indicate alluvial fans, crater floor, and fill/mantling deposits within impact craters >50 km in diameter in southern Margaritifer Terra were likely emplaced during multiple epochs: fans formed during the Amazonian or near the Amazonian-Hesperian boundary, crater floor deposits are likely Hesperian in age, and most fill/mantling deposits are Amazonian. The regional distribution of fans points to a late period of widespread water-driven degradation. Two of the final candidate landing sites for the 2011 Mars Science Laboratory mission would land on or near some of these fans, which appear younger than previously considered. Citation: Grant, J. A., and S. A. Wilson (2011), Late alluvial fan formation in southern Margaritifer Terra, Mars, Geophys. Res. Lett., 38, L08201, doi:10.1029/2011GL046844.
A population of large alluvial fans has been discovered on Mars. They emanate from crater rims and deposit into crater basins. The build up of such alluvial fans requires a sustained source of flowing surface water. However, the amount of water may vary and that variation can be recorded in variations in fan surface morphology and slope. About half of the alluvial fans on Mars preserve a surface fluvial record (e.g.stream patterns, meanders, cut banks) and the majority have slopes measurable at Mars Orbiter Laser Altimeter (MOLA) resolution. We are conducting experimental modeling of alluvial fan formation using the Eurotank at Utrecht University to understand the relative importance of sediment discharge and pre-existing basin slopes on alluvial fan morphology. The Eurotank Flume Facility contains a flume 5 by 8 meters. The water discharge, sediment discharge, basin structure, and particle size can all be varied. We conduct two experiments simultaneously; the resulting fans are deposited on two 2.5 by 5 meter prepared surfaces with constant slopes of ~0.035 and ~0.045, respectively. Sediment and water discharge are held constant. Results are recorded as a combination of surface images (from video recording of fluvial processes) and digital terrain models (DTM) at a resolution of ~80 microns from photogrammetry (stereo pairs) of the entire fan apron surface. The DTM and photographic results will be integrated with data from previous experiments of fan formation over lower sloping surfaces and the combined experiments will be compared to the Martian fan population. We will compare the experimental formation of surface fluvial features similar to those observed on Mars (e.g. stream patterns) with the goal of ascertaining the amount of fluid (i.e. debris flow vs. fluvial) required to form the Martian alluvial fans. Though we are currently focusing on Martian large alluvial fans, we anticipate that there will be broad applications to many of the fans discovered on Mars (i.e. delta fans and possible small debris flow fans) as well as terrestrial alluvial fan formation processes.
Model evaporite crystals grown in the laboratory to incorporate organic compounds and/or biomolecules have significant potential to test the various techniques proposed for the astrobiological exploration of Mars.
Impact craters on Mars may have created a range of aqueous environments conducive to life. Fluid inclusions have the potential to preserve organic matter, and have significant potential for astrobiological exploration within evaporites and hydrothermal systems in craters.
We compare DTM data of Mars and of controlled laboratory experiments with a morphological model to infer sediment transport mode, surface processes, formative duration and climatic conditions at the time of formation.
Palos crater, a prominent candidate crater-lake site in the Hesperia region of Mars, is located at the mouth of a sinuous inlet channel that extends from the northern flanks of Tyrrhena Patera. Previous studies of this site have concluded that channels and basin-infill units likely formed through aqueous processes that partly involved karst-like removal of materials in the subsurface by the flow of groundwater. As with many locales on Mars, the aqueous processes hypothesized to have been involved in the formation and evolution of terrain features are compelling. However, the characteristics of this site suggest that an alternative set of mechanisms for landform development should be considered alongside aqueous hypotheses. The main attributes of channels and infill of the central crater include: (1) an association with a very large volcanic rise to the south; (2) the existence of roofed segments of the main inlet channel; and (3) infill of the central crater and outlet channel by materials that have characteristics consistent with those expected of volcanic plains. These general attributes are consistent with formation through or in association with processes that involved the flow of lava. Although a volcanic model may account for the presence and basic nature of landforms previously considered supportive of a paleolake interpretation of the site, an overprint of dendritic valley networks on parts of the inlet system suggests that aqueous processes may have also acted in the evolution of the site. A complex interrelation between past igneous and aqueous processes at this site is possible.
Liquid water is not currently stable on the surface of Mars, but images
provided by the Mars Orbiter Camera aboard the Mars Global Surveyor
spacecraft reveal erosional landforms previously interpreted to be
geologically young gullies formed by groundwater seepage. We test the
basic hypothesis that, as on Earth, the location of these gullies is
controlled in part by the presence of an impermeable rock layer
(aquiclude) and that the depths of the gully heads below the surface
should thus be correlated to subsurface geology. We show that (1)
gullies emanate from a specific cliff-forming layer, even if the layer
is faulted, and (2) the depth of gullies below the local surface ranges
from 70 to 800 m, and (3) is positively correlated to mapped geologic
units. Gully formation is therefore dependent upon both favorable
climatic conditions to produce and sustain liquid water and the presence
of impermeable subsurface layers to collect the groundwater. Gullies may
mark the distribution of subsurface impermeable layers globally, and are
prime targets for the search for present water and life on Mars.
The role of water in carving the Martian outflow channels has recently
been challenged by the hypothesis known as ``White Mars.'' This
hypothesis claims that the channels were cut by CO2
gas-supported debris flows that also resurfaced the northern plains.
However, proposed analogs of ``cryoclastic'' flows are either
inappropriate (i.e., submarine density flows) or are primarily
depositional rather than erosional (i.e., pyroclastic flows). Subaerial
mass movements on Earth do not carve long deep channels like those on
Mars. I review runout efficiencies for mass movements on Earth and Mars.
The efficiencies required for ``cryoclastic'' flows to resurface the
northern plains of Mars are so large that they appear unattainable.
White Mars seeks to resolve carbonate and floodwater ``paradoxes'' that
probably do not exist. It is also doubtful whether reservoirs of
CO2 could persist over geologic time in the crust. Overall,
the CO2 hypothesis fails key tests and should be abandoned as
a means to carve outflow channels. I present a new interpretation of the
fluid source that created Aromatum Chaos and Ravi Vallis. Water, not
liquid or gaseous CO2, was the causative fluid, and the
source was an ice-covered impoundment in ancestral Ganges Chasma. At
that time the canyon had no eastern outlet, and groundwater flowed
northward to discharge at Aromatum Chaos and Shalbatana Vallis. The
presence of ice-covered water bodies can help to calibrate models of
volcanic-hydrologic climaxes during Hesperian time. The outflow
channels, like the spectacular landforms of the Channeled Scabland, are
monuments to the erosive power of catastrophic aqueous floods.
Secondary minerals near and within fractures in Columbia River basalts contain objects the size and shape of bacteria. These bacteriomorphs are most commonly rods or ellipses but also include cocci and diplococci forms, vibrioids and club-shaped rods, and associated pairs of objects that suggest cellular division by binary fission. Secondary minerals associated with, enclosing, and making up bacteriomorphs include iron oxyhydroxides, sulfides, and smectites containing ferrous iron. The secondary minerals are intimately intermixed with kerogen. Moreover, bacteriomorphs in the pyrite consist of kerogen. Careful consideration of mineral associations, the occurrence of organic carbon, and the spatial context of bacteriomorphs indicate that they are microfossils. The association of microfossils with minerals formed in reducing environments suggests an ancient ecosystem dominated at least in part by sulfate-reducing bacteria, similar to communities within these basalts today.
The recent discovery of ALHA81005, a small meteorite that undoubtedly came from the moon, has raised questions about how an intact rock fragment could survive acceleration to planetary escape velocities. This acceleration could only have been produced by a large impact on the lunar surface. A small amount of material (0.005 to 0.02 projectile volume) may be ejected from an impact crater at speeds exceeding lunar escape velocity without suffering petrographically detectable shock damage. The ejected material is protected by stress-wave interference close to the free surface. The existence and size of this zone depend upon parameters such as the rise time of the stress pulse produced by an impact. The fragment size is a function of ejection velocity. The lunar meteorite was ejected during an impact event that produced a crater at least 3.6 km in diameter. Other meteorites may have originated in a similar way.
To understand the conditions under which microorganisms exist in deep hydrocarbon reservoirs, sidewall cores were collected from a natural gas‐bearing formation, 2800 m below the surface in Taylorsville Basin, Virginia. Data from chemical and microbial tracers and controls indicate that the interiors of some sidewall cores contained microorganisms indigenous to the rock formation. The cultured microorganisms were composed primarily of saline‐tolerant, thermophilic fermenting, Fe(III)‐reducing, and sulfate‐reducing bacteria (1 to 10 cells/g). The physiological capabilities of the cultured microorganisms are compatible with the temperature (76°C), pressure (32 MPa), and salinity (≈0.8 wt.% NaCl equivalent) in the sampled interval. The petrological data indicated that the strata contain intercrystalline pores of micrometer size, that occur between late diagenetic cement in siltstone and within cross‐cutting, mineralized fractures in shale. These pores made up only 0.04% of the rock volume, were mostly gas‐filled, and were interconnected by pore throats with diameters 0.1% of the viable bacteria. The recovery of living bacteria from such an austere environment represents one of the most remarkable examples of microbial survival yet reported.
For activity and survival in extreme terrestrial Antarctic habitats, lithobiontic cyanobacteria depend on key biomolecules for protection against environmental stress and for optimization of growth conditions. Their ability to synthesize such molecules is central to their pioneering characteristics and major role as primary producers in Antarctic desert habitats. Pigmentation is especially important in protecting them against enhanced UVB damage during stratospheric ozone depletion (the Ozone Hole) during the Antarctic spring and subsequent photoinhibition in the intense insolation of the summer. To be effective, especially for the screening of highly shade-adapted photosystems of cyanobacteria, protective pigments need to be located strategically. Antarctic lithic cyanobacterial communities are therefore stratified, as in soil biofilms of Alexander Island, the benthic stromatolitic mats of ice-covered hypersaline lakes in the McMurdo Dry Valleys, and the endolithic communities within translucent Beacon sandstone outcrops of Victoria Land. The protective pigments include scytonemin, carotenoids, anthroquinones and mycosporine-like amino acids. To detect and locate photoprotective pigments in situ in free-living cyanobacteria and cyanolichens from hot and cold desert habitats, we have used Fourier-transform Raman microspectroscopy. With appropriate power inputs for labile molecules, this high-precision, non-intrusive laser-based technique can not only identify biomolecules in their natural state but also locate them spatially within the habitat relative to the components of the community, which require protection. In conjunction with direct and epifluorescence microscopy it provides a spatial and functional description of the protective strategy of a community. We present the unique Raman spectrum of scytonemin and use its primary and corroborative peaks to identify it within the plethora of other biochemical constituents of several natural cyanobacterial communities, including an Antarctic endolith. The remote-sensing aspect of this technique makes it suitable not only for spatial biochemical analysis of present and palaeontological Antarctic communities but also for analogous putative habitats on Mars.
Natural levels of ultraviolet (UV) radiation can harm organisms in shallow aquatic ecosystems in which concentrations of photoprotective dissolved organic carbon are low. These compounds can be removed as a result of acidic precipitation and climate changes, an effect which may have recently been manifested in up to 200,000 boreal lakes. Unfortunately, meteorological and biological monitoring studies are usually too brief to record the magnitudes of past changes in UV radiation fluxes and their effects. Here we demonstrate that certain fossil pigments in lake sediments can be used to document historical changes in the UV radiation environment of lakes. These pigments are produced by benthic algae when exposed to UV radiation and show sedimentary concentrations that are correlated to the depth of penetration of UV radiation within lakes. Analysis of fossil profiles from the sediments of two mountain lakes suggests that past UV radiation penetration has sometimes been-at least in these mid-latitude lakes-greater than dining the period of anthropogenic stratospheric ozone depletion.
Laser-based Fourier-Transform Raman spectroscopy (FTRS) has been used to identify in
situ compounds of ecophysiological significance in diverse field-fresh Antarctic cryptoendolithic microbial communities. FTRS does not disrupt the community and permits characterization of visible and invisible compounds in their natural configuration within cells and their current or former microhabitat. The small “footprint” of the microscopic laser beam permits accurate analysis of discrete zones of compounds produced by extant or degraded micro-organisms with minimum destruction of the biota. This spatial chemical analysis is applicable to any translucent or exposed habitat or biotic assemblage. Two hydrated forms of biodegradative calcium oxalate were differentiated in black-pigmented and hyaline lichen zones of endolithic communities. The oxalate was restricted to zones containing fungi. Communities dominated by cyanobacteria at Battleship Promontory (77°S) and a newly discovered site at Timber Peak (74°S) contrasted chemically with those dominated by eukaryotic algae at East Beacon (78°S). FTRS also showed the zonation of pigments including chlorophyll and UV-protective carotenoids in situ. At extreme sites on the polar plateau, it revealed the presence of “fossil” endolithics where detrimental climatic changes had made the microbes non-viable or amorphous, being represented solely by their residual bio-molecules. The technique has potential for past or present life-detection anywhere in the world without destruction of the microniche.
Sequence alignments between membrane-spanning segments of pheophytin-quinone-type photosynthetic reaction centers, FeS-type photosynthetic reaction centers, core chlorophyll-proteins of PS II, chlorophyll t a/t b-containing antenna proteins of plants and light-harvesting complexes of purple bacteria led us to postulate a large common ancestral pigment-carrying protein with more than 10 membrane spans. Its original function as a UV-protector of the primordial cell is discussed. It is conceivable that a purely dissipative photochemistry started still in the context of the UV-protection. We suggest that mutations causing the t loss of certain porphyrin-type pigments led to the acquisition of redox cofactors and paved the way for a gradual transition from dissipative to productive photochemistry.
Vertical distribution of fossil carotenoids in a sediment core from meromictic Mahoney Lake was studied. Besides okenone and demethylated okenone, lutein and zeaxanthin andβ-carotene isomers were identified. No carotenoids typical for purple nonsulfur or green sulfur bacteria were detected. The ratio of zeaxanthin to lutein (above 1:1 in all samples) indicates a dominance of cyanobacteria over green algae in the phytoplankton assemblages of the past. Okenone, which is found exclusively in Chromatiaceae, was the dominating carotenoid in all sediment zones.
The oldest sediment layers containing okenone were deposited 11 000 years ago. Between 9000 and 7000 and since 3000 years b.p., Chromatiaceae reached a considerable biomass in the lake. Vertical changes in okenone concentration were not related to changes of paleotemperatures. In contrast, okenone concentrations decreased during periods of volcanic ash input. During most of the lake history, however, mean okenone concentrations were positively correlated with sedimentation rates. This indicates that vertical changes of okenone concentration in the sediment reflect past changes of purple sulfur bacterial biomass in the lake.
According to these results, the past limnology of Mahoney Lake resembled that of the present with a sulfide-containing monimolimnion and a well-developed population of okenone-bearing purple sulfur bacteria.
A revised Martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment. This analysis differs from previous studies by using Viking 1:2M photomosaics to map all 25,826 craters ⩾8km diameter which postdate the lithologic units making up the Martian surface. The relative plotting technique is used because it shows changes in the shape and density of the crater size-frequency distribution curves more clearly than cumulative plots. The changes in shapes of the distribution curves are interpreted to be due to two different impacting populations, one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period. The 8-km-diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet. The results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 10⁵ km².
This study surveys the evolution of martian impact crater paleolakes through time by establishing their age, comparing their locations, and describing the formation of lacustrine sedimentary structures and features over time. We explore their meaning in terms of global climate changes, but also on local and regional scales. We observe a co-location between recent impact crater paleolakes and regions where GCM modeling shows that Mars is currently experiencing days above triple point and below boiling point of water. Some source areas show morphologies that could be consistent with ancient glacier features in the Argyre Basin/Darwin Crater region, in locations that are also consistent with GCM models of past snow precipitation on Mars. We propose that, at least for some paleolakes, our results are best explained by recent, and abundant, aqueous activity on Mars, with some meteorological contribution. These results are supported by other recent findings on martian meteorite ages, by the analysis of new MGS data showing recent volcanic and fluvial activity, and by climate modeling. They point toward the possibility that Mars currently is only hydrologically dormant and that there is a potential for hydrological activity to be generated again in the future following changes in the planet's orbital parameters.
Solar radiation is an important driving force for hydrological and biological systems in the dry valleys, influencing sublimation and melting of the glaciers, heating of the soils and air, and providing energy for photosynthesis by the microbial communities in the streams, soils, and perennially ice-covered lakes. We analyzed two years of solar radiation data from eleven meteorological stations positioned on glaciers, lake shores, and lake ice in Taylor, Wright, and Victoria Valleys. Average annual incoming solar radiation ranged from 84 to 117 W m⁻² during 1994 and 1995. We attribute differences among stations primarily to terrain effects, but coastal cloudiness and orographic effects may also be factors. Average annual net solar radiation was 59 to 76 W m⁻² at the soil-covered sites, while net solar radiation at glacier and lake-ice sites was lower, 18 to 52 W m⁻², due to the high albedo of snow and ice. Terrain obstructions were especially apparent in diurnal time series for Lake Hoare, even in December when the sun is at its highest position. Because of the importance of terrain on solar radiation patterns, we applied a topographic solar radiation model to Taylor Valley, using in situ pyranometer data to drive the model. Considerable topographic variability in solar radiation occurs over the region, even averaged over a monthly time scale, with north facing slopes receiving more energy than south facing slopes. In the valley bottom, differences in incident radiation were discerned among lakes, with Lake Fryxell receiving uniform amounts of energy while Lakes Hoare and Bonney received less energy along their northern shores due to terrain shading. Hourly radiation maps and pyranometer data illustrate that the terminus of the glaciers receive higher levels of solar radiation than their surface, but this intense illumination is of short duration, occurring only when the sun directly strikes the cliff face.
Stromatolitic microbial mats composed primarily of bacteria, cyanobacteria, eukaryotic algae are found in the cold, dimly-lit, perennially ice-covered antarctic lakes of southern Victoria Land, Antarctica (77°32-43’S, 161° 33’ -163°7’ E). The morphology of a particular mat results from a combination of biological, geochemical, and sedimentological processes, some of which may be unique to ice-covered lakes. Prostrate, lift-off, columnar, and pinnacle mats are trapping, binding and/or precipitating carbonates and various other minerals forming organosedimentary structures. The ice-covered lakes of Antarctica may serve as an important model for understanding the formation of stromatolites in cold environments. Studies of antarctic stromatolitic mats enhance our understanding of the range of environmental conditions capable of supporting stromatolite formation, particularly cold facies including those present during the Precambrian.
For most solids, shock wave pressures in the range extending from 100 kilobars to 400 kilobars are attained easily. Pressures in excess of 1000 kilobars can be obtained by the slight modification of the simple in contact explosive–solid geometry. The task of determining the associated pressure–compression data derives part of its appeal from the fact that precise static compressibility studies have been limited to pressures below 100 kilobars. The experimental approaches to the problem of determining the pressure–compression states behind shock waves are reviewed and a summary of the published experimental data for solids is given in the chapter. The experimental data that consist of a known pressure P, volume V, energy E locus for each material are extended to a complete thermodynamic description of states neighboring the experimental curves. These calculations are based upon the Mie–Grüneisen equation of state and the Dugdale–MacDonald relation, the latter being used to determine the volume dependence of the Grüneisen ratio. The Dugdale–MacDonald relation is tested at zero pressure, where sufficient thermodynamic data exist to permit the comparison with Grüneisen's ratio as calculated from the usual thermodynamic relations.
Postshot exploration around the 61 ± 10 kT Piledriver underground
nuclear explosion in granodiorite indicates that the cavity radius
rc is 40.1 meters. The shape of the vertical chimney, which
extends 277 meters above the shot level, was influenced by pre-existing
joints and fractures and is asymmetric. The limit of detectable
shock-induced microfracturing is 2.7 ± 0.2 rc, at
which point rocks have been subjected to peak radial pressures of 6-8
kb. Extensive fracturing occurs at distances to the shot point of
<1.3 ± 0.2 rc, corresponding to pressures exceeding
the granodiorite Hugoniot elastic limit of 45 kb. The onset of slip and
twinning in mineral constituents is correlated with measured shock
pressures at estimated strain rates of ≤104-105
sec-1, ambient temperatures of 30°C, and calculated
Hugoniot temperatures for granodiorite of <300°C. For quartz,
planar lamellas are detectable in some grains subjected to pressures of
75-78 kb and in all grains subjected to a pressure of 205 kb. Mechanical
(1¯01) twinning in hornblende and sphene <110> is evident in
rock that has experienced pressures of 24-40 and 14-18 kb, respectively.
Some kinking in biotite is associated with shock pressures as low as
15-16 kb; above 75 kb all biotite contains kink bands. At ≤270 kb no
shock-induced twinning or planar lamellar structure was noted in either
the orthoclase or the albite-oligoclase component of the granodiorite,
although there was a noticeable loss of birefringence in both. Glass
occurs within the chimney rubble and in distant fractures within the
surrounding granodiorite where it was injected by expanding gases. No
diaplectic glass was noted in rock forming the cavity walls (270 kb).
Dissociation of the hydrous phases, biotite and hornblende, in wall rock
surrounding the cavity is attributed to the permeation of hot gases
along fractures.
Bacterial communities were detected in deep crystalline rock aquifers within the Columbia River Basalt Group (CRB). CRB ground waters contained up to 60 {mu}M dissolved H{sub 2} and autotrophic microorganisms outnumbered heterotrophs. Stable carbon isotope measurements implied that autotrophic methanogenesis dominated this ecosystem and was coupled to the depletion of dissolved inorganic carbon. In laboratory experiments, H{sub 2} a potential energy source for bacteria, was produced by reactions between crushed basalt and anaerobic water. Microcosms containing only crushed basalt and ground water supported microbial growth. These results suggest that the CRB contains a lithoautotrophic microbial ecosystem that is independent of photosynthetic primary production. 38 refs., 4 figs., 3 tabs.
The objective of this study was to determine the survivability of osmophilic microorganisms in space, as well as examine the DNA breakage in osmophilic cells exposed to solar UV-radiation plus vacuum and to vacuum only. The organisms used were an unidentified species of Synechococcus (Nägeli) that inhabits the evaporitic gypsum-halite crusts that form along the marine intertidal, and an unidentified species of the extremely halophilic genus Haloarcula (designated as isolate G) isolated from a evaporitic NaCl crystal. Because these organisms are desiccation resistant and gypsum-halite as well as NaCl attenuate UV-radiation, we hypothesized that these organisms would survive in the space environment, better than most others. The organisms were exposed to the space environment for 2 weeks while in earth orbit aboard the Biopan facility. Ground controls were tested in a space simulation facility. All samples were compared to unexposed samples. Survivability was determined by plate counts and the most probable number technique. DNA breakage was determined by labeling breaks in the DNA with 32P followed by translation. Results indicate that the osmophilic microbes survived the 2 week exposure. The major cause of cell death was DNA damage. The number of strand breaks in the DNA from vacuum UV exposed cells was greater than the vacuum only exposed cells.
The harshness of the environment at its surface severely limits the survival of unprotected terrestrial organisms on Mars. However, the Martian geologic record is consistent with an earlier history with much different climatic conditions, more conducive to life, followed by an extended climate change which led to the currently inhospitable state. Such a transition is ideal for evolutionary adaptation to new conditions because it provides both the forcing function and the extensive time for progressive specializations. It is shown that against each of the current limits to life (organics deprivation; restricted amounts and physical forms of H2O; limited availability of other key nutrients; ionizing radiation insult; and strongly oxidizing chemical species), there are plausible countermeasure solutions. Most, but not all, of these mechanisms already exist as known examples in terrestrial biota. A combination of these adaptations could conceivably allow highly tailored organisms, either active or dormant, to survive at or very near the surface of Mars. Even in carefully preserved regolith samples returned to Earth, microorganisms could be difficult to detect without specific biochemical probes and/or purposeful biological amplification by selective enhancement of the supply of nutrients, optimized incubation parameters, and highly sensitive detection of metabolic activity.
The cyanobacterial fossil record is among the oldest for any group of organisms, possibly reaching back to 3500 Ma ago. The molecular phylogeny of cyanobacteria is complementary to the fossil findings, confirming the antiquity of the group, the role of cyanobacteria in the evolution of planetary primary production, and the symbiotic origins of plastids in algae and plants from cyanobacterial ancestors. The study of fossil cyanobacteria followed the discovery of Precambrian microbial fossils by S.A Tyler and E.S. Barghoorn in 1954, and is still developing. Most fossil cyanobacteria are preserved in permineralized conditions in cherts and phosphorites or as organic compressions in shales. The interpretation of fossil cyanobacteria is aided by the study of modern counterparts, preferably within their natural habitats. These comparisons include the post mortem degradation of cellular remains. The fortuitous preservation and fossilization of ancient cyanobacterial communities in growth position, i.e. in the synsedimentary context, allows one to draw conclusions about their palaeoenvironment, including interactions between cyanobacteria and ancient sediments. These relations are based on cyanobacterial ecological requirements, and they compare well with behavioural responses of modern cyanobacteria in microbial mats and modern stromatolites. The general trend in the evolution of cyanobacteria is one of gradually increasing complexity and diversity, but the group shows a conservative maintenance of morphological adaptations to successful ecological niches. Accordingly, a large proportion of ancient morphological types is still represented among modern cyanobacteria. Fossil to Recent counterparts are identified for several coccoid and filamentous cyanobacteria. Evidence for heterocystous cyanobacteria is indirect, through identification of fossil akinetes.
Evidence of lakes in Mars history is substantial. The proposed similarities between the ancient Martian environment and certain modem environments on Earth have led exobiolo- gists to study antarctic lakes as analogs to those purported to have existed on Mars. We have investigated modem sedimentation processes (especially with respect to $3C of carbonate and organic matter) in lakes in the McMurdo Dry Valleys region of east Antarctica and assessed various palcolake deposits with respect to their utility as Martian analogs and targets for future Mars exobiology missions. Three main types of palcolake deposit were identified and assessed: strand lines, perched deltas, and lacustrine sand mounds. Deltas are usually identified as good targets, but our research shows that authigenic carbonates are not readily identifiable in the sediments. Large deltas, although most likely to attract attention throu:jremote sensing, gen- erally are difficult sites for discovery of palcobiological matter, and 5 C signals follow no co- herent pattern Lacustrine sand mounds, on the other hand, contain abundant authigenic car- bonate and freeze-dried organic matter and appear to be excellent records of paleolimnological conditions. The advantage of studying lake bottom deposits versus lake edge deposits is re- tricval of a stable lake-wide signal. Deltas are therefore most useful in that they are generally large-scale features capable of drawing attention to a region of potential for the discovery of smaller lacustrine sand mounds.
Mars holds great interest for exobiology and presently stands center stage in our plans to explore the inner solar system for signs of past or present life. With the spectacular success of the Pathfinder mission [Golombek, 1997] and upcoming mapping efforts by the Mars Global Surveyor orbiter [Albee et al, 1998], it is an especially appropriate time to revisit some important issues in Mars exobiology. The papers making up this Journal of Geophysical Research‐Planets special issue on Mars were the outgrowth of an American Geophysical Union special session entitled “Exploring for a Martian Biosphere,” which was presented at the fall meeting in San Francisco in 1995 [Farmer, 1995a]. Together these papers provide a context for evaluating some fundamental issues in the exobiological exploration of Mars. Topics covered fall into the following broad categories: (1) environments and conditions required for the origin of life (hydrothermal environments as sites for prebiotic chemical synthesis [Shock and Schulte, this issue]), (2) early Martian environments as a context for the evolution and diversification of life on Mars (early impact hazards [Sleep and Zahnle, this issue], early volatile and climate history of Mars [Haberle, this issue], and ice‐covered lakes as habitats for early life [Doran et al., this issue]), (3) exploring for extant Martian life (results of the Viking missions [Klein, this issue], environmental extremes for Martian life [Clark, this issue], and planetary protection and Mars sample return [DeVincenzi et al., this issue]), and (4) exploration strategies (phosphate minerals as targets for chemofossils [Mojzsis and Arrhenius, this issue] and the role of robotic surface missions [Stoker, this issue]).
Chemical biosignatures may consist of biomarkers or nonrandom mixtures of lipids or other compounds that could not have been assembled by abiogenetic processes. The most obvious of these are repeating structural subunits, reflecting the biosynthetic assemblage of lipids. Biosignatures may eventually be a critical component in recognizing extraterrestrial life. Taxon-specific biomarkers (TSBs) are recognized as complex biosynthetic molecules (biomarkers) that are utilized or synthesized by one specific group of organisms. Thus, they are signature compounds with demonstrated efficacy for tracing evolutionary history and the early development of the Earth's biosphere. Examples of TSBs and how they are used are exemplified by steranes (earliest eukaryotes), 2-methylhopanes (oxygenetic photosynthesis), 24-n-propylcholestanes (chrysophyte algae), triaromatic and saturate dinosteroid hydrocarbons (dinoflagellates), triaromatic 23,24-dimethylcholesteroids (dinoflagellates, haptophyles), 24-isopropylcholestanes (porifera), 24-norcholestanes (diatoms), and oleananes (angiosperms). Occurrence of TSBs before the recognized appearance of the taxa they represent is viewed as a new opportunity to obtain an early record of evolution. When applied to major taxa, important information about Earth's ancient environments can be determined.
established. However, recent experimental observations and theories based on localized, nonhomogeneous shear deformation and a transient nonuniform thermal state appear to provide a reasonable qualitative picture. In the present work, some of the terminal and transient shock-compression features observed in brittle solids are reviewed with particular emphasis on Hugoniot release-wave measurements. The possibility of instabilities in the laws governing shear deformation leading to observed heterogeneous deformation is considered, and although an elementary model is treated, the method shows promise of predicting the material and kinematic properties governing occurrence, growth, and frequency of localized deformation features. Transient stress wave calculations in crystalline quartz demonstrate how the kinematic environment governing instability growth is established under shock-wave compression. In addition, the transient nonuniform thermal state resulting from heterogeneous deformation is shown to provide a possible explanation for the observation of both 'fluidlike' and 'solidlike' shock release waves depending on the competing properties of thermal diffusion, melting temperature, and degree of thermal localization. The analysis shows a striking difference between those minerals which do, and do not, undergo a shock-induced phase transition and leads to speculated similarities between the kinetics of shock-induced phase transformation in brittle solids and the kinetics of thermal detonation in explosives.
In this review the authors discuss the formation of Antarctic sea ice and saline lakes, consider the ultimate physico-chemical factors controlling the lower temperature limits of prokaryotic life and review the basis of one of the major physiological adaptations necessary for psychrophilic growth, the lipids of the cell membrane. -from Authors
First-order polymorphic, second-order, melting, and freezing transitions induced by shock-wave loading are reviewed. Comprehensive tabulations of the experimental observations are presented and materials that have been subjected to in-depth study are reviewed in more detail. Theories of the mechanics, thermodynamics, kinetics, and shear strength of shock-loaded materials are described and experimental techniques are briefly reviewed.
Robotic missions to Mars require remote diagnostic tools for detecting
evidence of former life. Laser Raman spectroscopy is eminently suitable
for this quest as its light-scattering principle permits nonintrusive
analysis. Integration of Raman spectroscopy with optical microscopy
correlates biochemical and morphological data. Vibrational Raman spectra
identify component moieties of unknown target biomolecules such as
pigments involved in photosynthesis and UV-protection. Antarctic desert
analoges of potential early Mars habitats support localized anaerobic
photosynthetic bacteria and widespread cyanobacteria containing
chlorophyll as a primary pigment. Chlorophyll and accessory pigments
(e.g. phycocyanin) autofluoresce at visible wavelengths (e.g. 530 nm).
Although valuable for epifluorescence microscopy, this interferes with
Raman spectra by producing curved baselines and instrument saturation.
Fourier Transform Raman spectroscopy (FTRS) with near-IR excitation
avoids most fluorescence while producing distinct and unique spectra for
a wide range of wavenumbers. These spectra identify key moieties, such
as the porphyrin nucleus of chlorophyll, which can be detected in whole
communities from deserts with features common to potential habitats of
early Mars.
Geological mapping of the Gusev Crater-Ma'adim Vallis region is part of a NASA program to investigate potential landing site areas on Mars. Two photomosaics at 1:500,000-scale and individual Viking images with resolution of 63-68 m/pixel were used as the base for the geologic mapping. The area is included in the Aeolis subquadrangle of Mars and is located in the transitional zone between the lowlands of the Elysium basin to north and oldest highland plateaus to the south. The 160 km diameter Gusev Crater and Ma'adim Vallis are located in the central part of the map area. The crater served as a long-term sedimentary basin for Ma'adim Vallis. In addition, an unnamed sedimentary basin (300 km in diameter) is located to the west of Gusev Crater. This basin accumulated sediments from both Ma'adim Vallis and other fluvial systems during Upper Noachian-Middle Amazonian periods.
Episodes of confined flows in Ma'adim Vallis are reconstructed by surveying the terraces in the valley. Three major levels and their associated tributary systems are identified and mapped. This study points out the evidence of the cessation of the valley activity between the formation of levels 1 and 2, characterized by degraded and large perched valleys, which floor are not adjusted to the following flow episode level. A strong asymmetry in the tributary distribution points toward a groundwater-supplied water origin of the valley. Potential source areas are demonstrated to be in volcano-tectonic regions, implying a hydrothermal origin of the water, that may include melted permafrost. Calculation of hydraulic radii, valley sections, and models of discharge rates associated with the morphologic and geologic survey shows that Ma'adim Vallis was an episodic channel, the lifetime of which spanned between the Noachian and Amazonian.
The cyanobacterium Nostoc commune has been developed as the prokaryotic model for the anhydrobiotic cell and it provides the means to answer fundamental questions about desiccation tolerance. The anhydrobiotic cell is characterized by its singular lack of water — with contents as low as 0.02 g H2O g-1 dry weight. These levels are orders of magnitude lower than those found either in bacterial spores or in cells subjected to acute salt (osmotic) stress. Mechanisms that contribute to the desiccation tolerance of N. commune include the selective stabilization of anhydrous proteins, the secretion of water- and lipid-soluble UV-absorbing pigments, and the secretion of a complex glycan that immobilizes the cells, immobilizes water stress proteins and the UV-absorbing pigments, and which may confer the properties of a mechanical glass upon colonies. Rehydration of desiccated cells induces an instantaneous resumption of metabolic activities, including membrane transport and global lipid biosynthesis. These initial recoveries may not follow classical Arrhenius-based kinetics. The rehydrating cell exhibits a stringent, stepwise recovery of physiological capacities beginning with respiration, then photosynthesis and finally nitrogen fixation. Protein turnover, de novo protein synthesis and a rapid rise in the intracellular ATP pool accompany these recoveries. During the early stages of rehydration, the de novo transcription of one gene set (rpoC1C2) is achieved using an extant DNA-dependent RNA polymerase holoenzyme that remains stable in desiccated cells. These properties of desiccation-tolerant cyanobacleria, present in extant forms such as N. commune and Chroococcidiopsis spp., may have been utilized by the eoanhydrobiotes. However, it is the desiccation-tolerant cyanobacterium as a whole, and not some collection of disparate properties, that must be considered as the primary strategy for the achievement of desiccation tolerance.
This paper reviews the literature on cold-adapted micro-organisms which might exist in ice and permafrost. Properly identified, microbial markers in the cryolithozone could be used in palaeoenvironmental reconstructions, in distinguishing between epigenetic and syngenetic depositional sequences, and in the recognition of secondary thaw unconformities. Cryobiological problems include (1) whether the bacteria are dead, dormant or in the active state, and (2) what factors determine the preservation of cell structures. A possible consequence of permafrost thawing, based upon predicted global warming scenarios, is that there may be an increase in microbial activity and an increase in active layer thickness.
Le présent article passe en revue la littérature portant sur les micro-organismes adaptés au froid qui peuvent exister dans la glace et le pergélisol. A condition d'étre correctement identifyés, les marqueurs microbiologiques présents dans la cryolithozone pourraient étre utilisés dans des reconstructions des palénvironnements en distinguant des séquences épigénétiques et syngénétiques du dépét et en reconnaissant les discontinuités dues aux dégels secondaires. Les problémes rencontrés consistent é déterminer: 1) si les bactéries étaient mortes, dormantes ou dans un stade actif, 2) quels sont les facteurs qui contrélent la préservation des structures cellulaires.
Le dégel du sommet du pergélisol en conséquence d'un réchauffement climatique global, provoquerait peut-étre en une augmentation de l'activité biologique en méme temps qu'une croissance de l'épaisseur de la couche active.
The porphyrin content and composition in the extractable organic matter has been analysed in 13 Kimmeridge clay source rocks, spread from the north to the south of the Norwegian continental shelf. The samples are predominantly immature/early mature. The distribution of nickel and vanadyl porphyrins within the samples is markedly different. Effects of the thermal maturity on the composition of porphyrins is evaluated and compared with biomarker parameters based on sterane and hopane ratios. Maturity is modelled using partial least-squares (PLS) multivariate analysis with Tmax as a maturity indicator. Porphyrin parameters based on the total carbon number distribution of DPEP and ETIO series from the mass spectral data of the nickel and vanadyl porphyrin fractions effectively describe the Tmax of the samples with a better correlation than aliphatic biomarker ratios. Selected porphyrin and biomarker ratios were used for principal component analysis (PCA) modelling, and found to describe two types of variation that may be indicative of the prevailing depositional redox conditions.
We analyzed noble gases from 18 samples of weathering products (“iddingsite”) from the Lafayette meteorite. Potassium‐argon ages of 12 samples range from near zero to 670 ± 91 Ma. These ages confirm the martian origin of the iddingsite, but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric ⁴⁰ Ar. In any case, because iddingsite formation requires liquid water, this data requires the presence of liquid water near the surface of Mars at least as recently as 1300 Ma ago, and probably as recently as 650 Ma ago. Krypton and Xe analysis of a single 34 μg sample indicates the presence of fractionated martian atmosphere within the iddingsite. This also confirms the martian origin of the iddingsite. The mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas.
Our strongest conclusion is that the iddingsite in Lafayette formed on Mars, in agreement with the microstratigraphic arguments of Gooding et al. (1991) and Treiman et al. (1993). A preterrestrial origin of the iddingsite is required both by the many non‐zero K‐Ar ages and by the presence of Xe that is isotopically distinct from any terrestrial Xe.
The Xe is accompanied by Kr, but the Kr and Xe have been fractionated if they are derived from the present martian atmosphere. This is presumably the result of either incorporation via interaction with liquid water (Drake et al. , 1994; Bogard and Garrison, 1998) or by adsorption from the martian atmosphere, perhaps accompanied by shock (see also Gilmour et al. , 1998, 1999). Although the iddingsite is enriched in Kr and Xe compared to whole‐rock analyses, it is not clear whether iddingsite is the dominant carrier of the atmospheric‐derived gas (Drake et al. , 1994) or merely a minor carrier (Gilmour et al. , 1999).
Our ⁴⁰ Ar‐ ³⁹ Ar experiment was disappointing, in that it mostly served to confirm that the iddingsite, which contains fine‐grained clays, is susceptible to recoil loss of ³⁹ Ar during irradiation. Only one sample of five gave a clear signal of radiogenic or extraterrestrial ⁴⁰ Ar, and that was only by 3°.
Potassium‐argon ages of the second set of samples were more successful, ranging from near 0 to 670 ± 91 Ma. It is not clear whether any or all of the ages represent iddingsite formation, as opposed to later alteration. The fact that a Rb‐Sr experiment (Shih et al. , 1998) gave an apparent age for iddingsite of 679 ± 66 Ma (2a) suggests that perhaps formation of iddingsite occurred (or began) ∼650 Ma ago and that some samples either formed, or were thermally altered, later. The ages could be even younger than 650 Ma, if the samples have incorporated martian atmospheric ⁴⁰ Ar.
This means that liquid water was certainly present on Mars in the last 1300 Ma (the formation age of Lafayette), and probably within the last 650 Ma.
Abstract— Using scaling relationships determined from nuclear explosions, the radial extent of the air blast produced by the Meteor Crater impact event is estimated. The wind velocity at a distance of 5 crater radii (3 km) from the point of impact should have exceeded 2000 km/h. Hurricane force winds would have existed as far away as 20 to 40 km, depending on the exact explosive energy of the impact event. To determine how this event may have affected the environment surrounding the crater, the topography, vegetation, and animal life that existed at the time of the impact are reconstructed. For example, if the coniferous woodlands were 100 m lower than they are presently and they had moved farther out onto the plains, then the air blast would have flattened trees within a 16 to 22 km radius of the point of impact and damaged them over an area of 4100 to 8500 km2. The distance over which the damage occurred may have been up to 2× larger in some directions around the crater because of additional effects produced by the ballistic shock wave. Unfortunately, since the trajectory of the projectile is not well known, the direction of the ballistic shock wave effects cannot yet be determined.
A bacterial strain belonging to the speciesThermus was isolated from the water of a Carlsbad hot spring at 70–73°C. The microorganism can grow aerobically and forms yellow
and orange colonies on a special medium, due to a carotenoid pigment. The growth optimum is 70–75°C. The minimum and maximum
temperatures for growth are 40 and 80°C, respectively. The microorganism is a Gram-negative, rod-like, immobile bacterium,
its characteristic feature being the ability to form long filaments (up to 200 µm long). The content of guanine and cytosine
in DNA is 65.1 %. This rare endemic microorganism was isolated and described in detail in Czechoslovakia for the first time.
It was included in theCzechoslovak Collection of Microorganisms of the Masaryk University in Brno and is available under the catalog number of CCM 4167.
The idea that life began elsewhere and then naturally migrated to the Earth is known as Panspermia. One such possibility is that life is carried on objects (meteorites, comets and dust) that arrive at the Earth. The life (bacteria) is then presumed to survive the sudden deceleration and impact, and then subsequently develop here on Earth. This step, the survivability of bacteria during the deceleration typical of an object arriving at Earth from space, is studied in this paper. To this end a two-stage light gas gun was used to fire projectiles coated with bacteria into a variety of targets at impact speeds of 3.8 to 4.9 km s–1. Targets used were rock, glass, metal and aerogel (density 100 kg m–3). Various techniques were used to search for bacteria that had transferred to the target material during the impact. These included taking cultures from the target crater and ejecta, and use of fluorescent dyes to mark sites of live bacteria. So far only one sample has shown a signal for bacteria surviving an impact. This was for bacteria cultured from the ejecta spalled from a rock surface during an impact. However, this result needs to be repeated before any firm claims can be made for bacteria surviving a hypervelocity impact event.
Measurements of the Hugoniot equations of state of hardened and annealed 2024 aluminum at pressures below 50 kbar are presented. The major aim of the experiments was to determine the validity of elastic‐plastic theory, which predicts that, at a given compression, the stress normal to the shock front is larger than the hydrostatic pressure necessary to produce the same compression by an amount equal to two‐thirds the yield strength in simple tension. Oblique shock geometry was employed. Shock and free‐surface velocities were recorded with a streak camera by means of a light‐reflection technique employing the principle of the optical level. This technique provides continuous recording of free‐surface motion with time, an essential requirement because of the existence of a double shock system. The observed elastic wave amplitudes (5.4±0.2 kbar and 0.9±0.2 kbar for hardened and annealed material, respectively) agree within experimental precision with values predicted from static tensile specimen data. The shock wave data, in the range 25–50 kbar, yield one‐dimensional strain isotherms which, while significantly different for the two different hardness conditions, agree within experimental precision with semitheoretical curves based on Bridgman's hydrostatic data to 30 kbar and on simple tension stress‐strain data. No significant strain rate effects are evident. It is concluded that elastic‐plastic theory is valid for the description of plane shock waves in this material.
CTH is a software system under development at Sandia National Laboratories Albuquerque to model multidimensional, multi-material, large deformation, strong shock wave physics. One-dimensional recti-linear, cylindrical, and spherical meshes; two-dimensional rectangular, and cylindrical meshes; and three-dimensional rectangular meshes are currently available. A two-step Eulerian solution scheme is used with these meshes. The first step is a Lagrangian step in which the cells distort to follow the material motion. The second step is a remesh step where the distorted cells are mapped back to the Eulerian mesh.
Water in the Martian atmosphere is 5.1 times more enriched in deuterium than terrestial water. The enrichment has been previously attributed to either a massive loss of water early in the planet's history or the presence of only a very small reservoir of water that has exchanged with the atmosphere over geologic time. Both these interpretations appear inconsistent with geologic evidence of large floods and sustained volcanism. Large floods are believed to have episodically introduced large amounts of water onto the surface. During a large flood roughly 1017 g of water would almost immediately sublime into the atmospher and be frozen out on polar terrain, to form a new layer several centimeters thick. The long-term effect of a flood would depend on where the water pooled after the flood. If the water pooled at low latitudes, all the water would slowly sublime into the atmosphers and ultimately be frozen out at the poles, thereby adding several meters to the polar deposits for each flood. If the water pooled at high latitude, it would form a permanent ice deposit, largely isolated from further interchange with the atmosphere. Volcanism has also episodically introduced water into the atmosphere. Most of this water has become incorporated into the polar deposits. That released over the last 3.5 Ga could have added a few kilometers to the polar deposits, depending on the amount of dust incorporated along with the ice. Large cometary impacts would have introduced additional large amounts of water into the atmosphere. The long-term evolution of D/H in the atmosphere depends on the rate of exchange of water between the atmosphere and the polar deposits. If exchange is active, then loss rates of hydrogen from the upper atmosphere are substantially higher than those estimated by Y. L. Yung, J. Wen, J. P. Pinto, M. Allen, K. K. Pierce, and S. Paulsen [Icarus 76, 146–159 (1988)]. More plausibly, exchange of water between the atmosphere and the polar deposits is limited, so that after eruptions, floods, and cometary impacts, the atmosphere soon becomes enriched in deuterium. According to this scenario, the atmospheric D/H is different from the bulk of the planet's water and so reveals little about the amount of water outgassed. The scenario implies, however, that the polar deposits are older and more stable than formerly thought.
Associations of immobilized microbial cells and organic-mineral complexes containing active enzymes are resistant to long-term (from tens of thousands to millions of years) effects of extremely low temperatures. This association enables the cells to restore their metabolic activity during permafrost thawing, because interactions with the heterogenous medium is made possible by the availability of active immobilized enzymes. The long-term effect of the cold probably favors an adaptational change of microbial metabolism that activates enzymes and cells during thawing.
The survey of the hydrogeologic system formed by Gusev crater and Ma'adim Vallis (Aeolis subquadrangle of Mars) points out evidence for the existence of an ice-covered lake in Gusev crater. A first lake was formed by the drainage of the aquifer in the region surrounding Gusev before the entry of Ma'adim Vallis in the crater. The existence of a former lake in Gusev is deduced from the morphology of the Ma'adim delta. Its comparison with terrestrial Antarctic analogs argues for the presence of an ice-covered lake in Gusev at the time that the southern part of the crater's rampart was breached by Ma'adim first release, and for a subice–lacustrine construction of the valley's delta. Our survey shows that Ma'adim Vallis may have entered Gusev crater as late as Late Hesperian/Early Amazonian as part of a second lake episode. The relationship between the variation of the Gusev lake water-level, the volume of the lake, and the surface of the lake bed is established by our bathymetric model. The elevation of the former lake is deduced from the elevation of the mesa-like structures in the delta of Ma'adim Vallis. Furthermore, the correlation of the crater frequency of Gusev rampart with Mars' stratigraphic age shows that lakes may have occupied Gusev crater over a period of time covering 2 Gyrs., from the formation of the crater to the last episode of water release from Ma'adim Vallis. Though it is most likely that the lake was episodical, the recurrence of abundant water in Gusev crater makes this site a high priority for missions, either for martian resource exploration, or for the search of life.
Many organisms from a wide variety of taxa have the ability to survive extreme dehydration, a phenomenon called “anhydrobiosis”. Concomitantly with resistance to the adverse effects of drying, these organisms are also resistant to the effects of freezing to very low temperatures, elevated temperature for brief periods, and the effects of ionizing radiation. One result of their resistance to environmental extremes is a greatly prolonged life span. The anhydrobiotes that have been investigated share a common metabolic adaptation, the production of certain disaccharides as a large proportion of their dry weight. Using these disaccharides, we have investigated the sources of damage attendant upon drying and the mechanisms by which anhydrobiotes and model systems of isolated membranes and proteins avoid damage. This report summarizes aspects of this work.