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A heat flow and physical properties package for the surface of Mercury
Abstract
European Space Agencies fifth cornerstone mission BepiColombo includes a ‘Surface Element’ to land a scientific payload on the surface of Mercury. The current strawman payload includes a heat flow and physical properties package (HP3), focussing on key thermal and mechanical properties of the near-surface material (down to a depth of 2– and the measurement of heat flow from Mercury's interior, an important constraining parameter for models of the planet's interior and evolution. We present here an overview of the HP3 experiment package and its possible accommodation in a self-inserting ‘mole’ device. A mole is considered to be the most appropriate deployment method for HP3, at least in the currently-assumed case of an airbag-assisted soft landing architecture for the Mercury Surface Element.
... Self-inserting 'moles' have the potential to measure a profile of mechanical (Pinna et al., 2001) and other properties as they advance through the host material, however like many techniques the properties of interest can be disturbed by the instrumentation, requiring modelling and careful experiment design and data analysis. An instrumented mole has been suggested for measurement of the heat flow and regolith properties on Mercury (Spohn et al., 2001). A further point worth highlighting is that mechanical measurements performed in the low surface gravity environment of NEOs may generate reactive forces or torques that must be balanced (e.g. by anchoring) to avoid ejecting the vehicle from the surface. ...
... Assuming in situ thermal measurements are needed for mitigation studies, there are of course techniques available that can be applied with only minor modifications. The measurement of sub-surface thermal properties—temperature profile and thermal conductivity (or, more easily, diffusivity)—can be achieved at a particular location by means of a string of heatable thermal sensors such as the PEN thermal probe of the MUPUS experiment on the Rosetta Lander (Seiferlin et al., 2001), or the mole-and tether-based sensors proposed for heat flow measurement on the surface of Mercury (Spohn et al., 2001). The MUPUS PEN probe is a 10 mm-diameter composite tube incorporating a 32 cm-long Kapton sheet, onto which 16 titanium heatable thermal sensors have been laser-sputtered. ...
... Other types of mole have been proposed, for example the Sub-Surface Explorer (SSX) (Wilcox, 2002) and the Inchworm Deep Drilling System concept (Rafeek et al., 2001). The mole-based experiment for heat flow and regolith properties measurements on Mercury (Spohn et al., 2001) illustrates some of the potential for integrating a suite of sensors into a mole for in situ experiments. The cometary mission Rosetta includes a 90 kg lander with a 26.7 kg payload designed to carry out a wide range of investigations on the nucleus of comet 46P/Wirtanen, including imaging, sample analysis and physical properties measurements (Biele et al., 2002). ...
NEO missions to be carried out in support of the selection and development of possible mitigation techniques will involve several investigations requiring operation of one or more surface elements on and/or under the surface of NEOs. The main examples are seismological methods, measurements of mechanical properties, measurements of sub-surface thermal properties and volatile content, emplacement of a radio beacon for orbit refinement, and radio transmission tomography. We describe the rationale behind such in situ investigations and some of the physical and technological constraints involved, drawing on heritage from a number of past and current missions and mission proposals. We describe the capabilities of ‘payload delivery’ penetrators and soft landers, and options for surface and sub-surface mobility. We conclude that a network of penetrators, possibly complemented by a mobile surface element, would best serve the requirements of surface-based NEO mitigation studies. Seismological methods would seem to represent the strongest driver in the definition of such a mission scenario. Many of the component technologies for such an approach exist already but integrated technological development and mission studies are currently needed in a number of areas.
... Although this is not rigorously justified, our rationale is that: 1) the temperature gradient at these depths is mainly proportional to the surface heat flux. Spohn, et al. (2000) [55], suggest that for Mercury this value should be a few times the lunar surface heat flux (~ 10 mW m-2 ). 2) even if we assume the same temperature gradient for the moon and Mercury the lithosphere of Mercury will be about 2/3 as thick as the lunar one. ...
... There is generous internal volume for accommodation of the lander avionics, power conditioning and science instruments. The strawman science instruments include an XRF spectrometer , multispectral imaging system, Raman/LIBS, seismometer and heatflow probe (Sims et al., 2003; Bibring et al., 2007; Mall et al., 2005; Wurz et al., 2004; Ahlers et al., 2007; Mimoun et al., 2007; Spohn et al., 2001). The sample acquisition system would be mounted on the underside of the lander. ...
Returning to the Moon has been advocated by a large number of international planetary scientists in order to answer several key scientific questions. The UK also has an active lunar science community keen to support (robotic) lunar exploration missions. However, for several years these interests have been eclipsed by the drive to Mars. Recently there is a renewed global interest in the Moon demonstrated by the Vision for Space Exploration in the USA, the evolving Global Exploration Partnership, and new lunar missions from Europe, Japan, China, India and the USA. The ESA Aurora programme may also broaden its focus to embrace the Moon as well as Mars—realizing that the risks associated with many of the major technical challenges that are faced by Mars missions could be reduced by relatively inexpensive and timely lunar technology tests. Surrey Satellite Technology Ltd. (SSTL) and Surrey Space Centre (SSC) have been preparing a 'smallsat' approach [] to achieving a low-cost lunar mission for more than a decade—including various activities, such as the earlier LunarSat study funded by ESA and a current hardware contribution to the Chandrayaan-1 mission. With the recent successes in GIOVE-A, TOPSAT and BEIJING-1, 1 alongside participation in Aurora and Chandrayaan-1, Surrey have developed capabilities for providing affordable engineering solutions to space exploration. Recently, SSTL/SSC was funded by the UK Particle Physics and Astronomy Research Council (PPARC) (now subsumed into the UK Science and Technology Facilities Council) to undertake a study on low-cost lunar mission concepts that could address key scientific questions. This paper presents some major results from this study [Phipps and Gao, 2006. Lunar mission options study. UK Particle Physics and Astronomy Research Council Report Reference No. 118537, pp. 1–104] and provides preliminary definitions of two mission proposals.
... To accomplish these objectives, a tightly focused payload has been identified consisting of several payload elements. These instruments are a seismometer (e.g., the Seismic Experiment for Interior Structure-SEIS, Lognonné et al., 2000), a magnetometer (e.g., the MAGnetic measurements instrument-MAG, Menvielle et al., 2000), a heat flow probe (e.g., the Heat Flow and Physical Properties Package-HP3, Spohn et al., 2001b), and a precision radio tracking geodesy experiment (e.g., the Rotation and Interior Structure Experiment-RISE, Dehant et al., 2009Dehant et al., , 2011. The landers will also have atmospheric sensors to measure the meteorological parameters such as temperature, pressure and wind, providing information necessary for interpreting the seismic observations as well as providing constraints for general circulation models (GCMs). ...
Our fundamental understanding of the interior of the Earth comes from seismology, geodesy, geochemistry, geomagnetism, geothermal studies, and petrology. For the Earth, measurements in those disciplines of geophysics have revealed the basic internal layering of the Earth, its dynamical regime, its thermal structure, its gross compositional stratification, as well as significant lateral variations in these quantities. Planetary interiors not only record evidence of conditions of planetary accretion and differentiation, they exert significant control on surface environments.
... Similar devices have been proposed or have been included on other space missions, although none have been successfully deployed, employing a variety of deployment techniques such as ballistic delivery (e.g. Urquhart et al., 2000, Tanaka et al., 2001) or hammering (Spohn et al., 2001, Spohn et al., 2007). On Earth a popular method for measuring thermal properties of materials, such as soils, liquids and gases, is the line-heat source. ...
The Philae lander is part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko. It will use a harpoon like device to anchor itself onto the surface. The anchor will perhaps reach depths of 1–2 m. In the anchor is a temperature sensor that will measure the boundary temperature as part of the MUPUS experiment. As the anchor attains thermal equilibrium with the comet ice it may be possible to extract the thermal properties of the surrounding ice, such as the thermal diffusivity, by using the temperature sensor data. The anchor is not an optimal shape for a thermal probe and application of analytical solutions to the heat equation is inappropriate. We prepare a numerical model to fit temperature sensor data and extract the thermal diffusivity. Penetrator probes mechanically compact the material immediately surrounding them as they enter the target. If the thermal properties, composition and dimensions of the penetrator are known, then the thermal properties of this pristine material may be recovered although this will be a challenging measurement. We report on investigations, using a numerical thermal model, to simulate a variety of scenarios that the anchor may encounter and how they will affect the measurement.
... Bulk density is one such parameter; instruments dedicated to its measurement were built and launched to the Moon, Mars and Venus 1 (see also Carrier et al. (1991) for a review of lunar surface bulk density data, and Moore et al. (1977 Moore et al. ( , 1999) for bulk density data from the Viking 1 & 2 and Mars Pathÿnder landers). Bulk density measurement has also been suggested for the BepiColombo Mercury lander , as part of a heat ow and physical properties package (Spohn et al., 2001 ). With the Rosetta mission to comet Wirtanen, the Rosetta Lander will allow physical properties of cometary nucleus material to be measured in situ for the ÿrst time. ...
The MUPUS experiment on the Rosetta Lander will measure thermal and mechanical properties as well as the bulk density of the cometary material at and just below the surface of the nucleus of comet 46P/Wirtanen. A profile of bulk density vs. depth will be obtained by measuring the attenuation of gamma rays emitted by a 137Cs source. Compton scattering is the dominant interaction process at this energy, the attenuation depending directly on the total number of electrons along the source–detector path. This in turn is approximately proportional to the column density. We report here on the design of the bulk density instrument and the results of related Monte Carlo simulations, laboratory tests and calculations of the instrument's performance. The 137Cs radioisotope source is mounted in the tip of the MUPUS thermal probe—a diameter rod, to be hammered into the surface of the nucleus to a depth of . Two cadmium zinc telluride (CZT) detectors mounted at the top of the probe will monitor the count rate of photons. Due to the statistics of photon counting, the integration time required to measure column density to a particular accuracy varies with depth as well as with bulk density. The required integration time is minimised for a material thickness equal to twice the exponential attenuation length. At shallower depths the required time rises due to the smaller fractional change in count rate with varying depth, while at greater depths the reduced count rate demands longer integration times. The former effect and the fact that the first of the source–detector path passes not through the comet but through the material of the probe, mean that the first density measurement cannot be made until the source has reached a depth of perhaps . The laboratory experiments indicate that at this depth an integration time no less than (falling to at full penetration) would be required to measure a bulk density of to 5% accuracy, assuming a source activity of (decayed from an initial ). Although solutions involving feedback of the measured bulk density into a time-budgeting algorithm are conceivable, a simple approach where equal time is spent per unit depth may be best, providing an accuracy in bulk density of around 5–20%, for slices and the expected range of parameters.
... Another instrument which is currently under development (for use on Mars and/or the Moon) is the so-called heat flow and physical properties package (HP 3 ), which was originally proposed as part of the payload for a Mercury lander to be flown with ESA's Mercury mission BepiColombo (Spohn et al., 2001). After the lander segment was canceled, efforts to develop a similar instrument for application on Moon and Mars have been continued and HP 3 became part of the Humboldt payload onboard ESA's ExoMars mission, until the entire geophysical package was descoped in early 2009. ...
The thermo-mechanical properties of planetary surface and subsurface layers control to a high extent in which way a body interacts with its environment, in particular how it responds to solar irradiation and how it interacts with a potentially existing atmosphere. Furthermore, if the natural temperature profile over a certain depth can be measured in situ, this gives important information about the heat flux from the interior and thus about the thermal evolution of the body. Therefore, in most of the recent and planned planetary lander missions experiment packages for determining thermo-mechanical properties are part of the payload. Examples are the experiment MUPUS on Rosetta's comet lander Philae, the TECP instrument aboard NASA's Mars polar lander Phoenix, and the mole-type instrument HP(3) currently developed for use on upcoming lunar and Mars missions. In this review we describe several methods applied for measuring thermal conductivity and heat flux and discuss the particular difficulties faced when these properties have to be measured in a low pressure and low temperature environment. We point out the abilities and disadvantages of the different instruments and outline the evaluation procedures necessary to extract reliable thermal conductivity and heat flux data from in situ measurements.
... Of course, LUNAR-A and MUPUS are by no means the end in the development of heat flow probes for planetary missions. Spohn et al. (2001) have suggested a heat flow probe for the surface element of the ESA's BepiColombo mission. A small, self-propelled penetrator termed 'mole' would dig into Mercury's regolith to a depth of several metres and carry out a heat flow measurement. Currently, a landing on Mercury within the framework of BepiColombo seems improbable, but the on ...
The year 2005 marks the 35th anniversary of the Apollo 13 mission, probably the most successful failure in the history of manned spaceflight. Naturally, Apollo 13's scientific payload is far less known than the spectacular accident and subsequent rescue of its crew. Among other instruments, it carried the first instrument designed to measure the flux of heat on a planetary body other than Earth. The year 2005 also should have marked the launch of the Japanese LUNAR-A mission, and ESA's Rosetta mission is slowly approaching comet Churyumov-Gerasimenko. Both missions carry penetrators to study the heat flow from their target bodies. What is so interesting about planetary heat flow? What can we learn from it and how do we measure it?
Not only the Sun, but all planets in the Solar System are essentially heat engines. Various heat sources or heat reservoirs drive intrinsic and surface processes, causing ‘dead balls of rock, ice or gas’ to evolve dynamically over time, driving convection that powers tectonic processes and spawns magnetic fields. The heat flow constrains models of the thermal evolution of a planet and also its composition because it provides an upper limit for the bulk abundance of radioactive elements. On Earth, the global variation of heat flow also reflects the tectonic activity: heat flow increases towards the young ocean ridges, whereas it is rather low on the old continental shields.
It is not surprising that surface heat flow measurements, or even estimates, where performed, contributed greatly to our understanding of what happens inside the planets. In this article, I will review the results and the methods used in past heat flow measurements and speculate on the targets and design of future experiments.
New complexes of 5‐methyl‐5‐(4‐nitrophenyl)‐hydantoin (L) with HgX2 (X = Cl−, Br−, and I−) were synthesized and characterized by several means including Fourier‐transform infrared (FT‐IR), proton nuclear magnetic resonance (1H NMR), carbon nuclear magnetic resonance (13C NMR), mass, CHN, and Energy Dispersive X‐ray analysis. The spectroscopic data verified the coordination of (L) to the Hg (II) metal centers from the oxygen atom of the carbonyl functional group. The resulting data show that the prepared complexes (1), (2), and (3) have a monodentate coordination mode to metal center and structures showing X‐bridged dimers. The cytotoxicity of the prepared complexes was investigated against cancer cell lines including MCF‐7 (breast), A549 (lung), and AGS (gastric) adenocarcinoma cells. The obtained data showed that complexes (1) and (2) represent a higher cytotoxic effect against the tested cells. Also, the antioxidant behavior study displayed notable antioxidant potencies for complexes (1) and (2) in comparison with ascorbic acid, as a standard. Also, for the theoretical study, density functional theory calculations at the BP86/def2‐SVP level of theory were applied. The strength and nature of donor−acceptor bonds between (L) and Hg fragments in the system of [L → HgX2]2 were performed by the use of the natural bond orbital analysis, energy decomposition analysis, and their natural orbitals for chemical valence variation. This paper explains the synthesis and characterization, theoretical study andbiological activity evaluation of a series of dimeric mercury (II) complexesderived from hydantoin ligand and mercury halides.
The Heat Flow and Physical Properties Package HP 3 for the InSight mission will attempt the first measurement of the planetary heat flow of Mars. The data will be taken at the InSight landing site in Elysium planitia (136 • E, 5 • N) and the uncertainty of the measurement aimed for shall be better than ±5 mW m −2. The package consists of a mechanical hammering device called the "Mole" for penetrating into the regolith, an instrumented tether which the Mole pulls into the ground, a fixed radiometer to determine the surface brightness temperature and an electronic box. The Mole and the tether are housed in a support structure before being deployed. The tether is equipped with 14 platinum resistance temperature sensors to measure temperature differences with a 1-σ uncertainty of 6.5 mK. Depth is determined by a tether length measurement device that monitors the amount of tether extracted from the support structure and a tiltmeter that measures the angle of the Mole axis to the local gravity vector. The Mole includes temperature sensors and heaters to measure the re-golith thermal conductivity to better than 3.5% (1-σ) using the Mole as a modified line heat The InSight Mission to Mars II Edited Page 2 of 33 T. Spohn et al. source. The Mole is planned to advance at least 3 m-sufficiently deep to reduce errors from daily surface temperature forcings-and up to 5 m into the martian regolith. After landing, HP 3 will be deployed onto the martian surface by a robotic arm after choosing an instrument placement site that minimizes disturbances from shadows caused by the lander and the seismometer. The Mole will then execute hammering cycles, advancing 50 cm into the sub-surface at a time, followed by a cooldown period of at least 48 h to allow heat built up during hammering to dissipate. After an equilibrated thermal state has been reached, a thermal conductivity measurement is executed for 24 h. This cycle is repeated until the final depth of 5 m is reached or further progress becomes impossible. The subsequent monitoring phase consists of hourly temperature measurements and lasts until the end of the mission. Model calculations show that the duration of temperature measurement required to sufficiently reduce the error introduced by annual surface temperature forcings is 0.6 martian years for a final depth of 3 m and 0.1 martian years for the target depth of 5 m.
Planetary heat flow probes measure heat flow (depth-resolved temperature and thermal conductivity) to provide insight into the internal state of a planet. The probes have been utilized extensively on Earth, twice on the Moon, and once on the Surface of comet 67P-CG. Mars is an important target for heat flow measurement as heat flow is a critical parameter in Martian thermal history models. Earlier studies indicate that Martian planetary heat flow can be accessed at 5. m below the surface in dry regolith monitored over at least one Martian year. A one Martian year monitoring period is necessary because, in the shallow subsurface, heat flow from the interior is superposed with time varying heat flow contributions, primarily due to insolation. Given that a heat flow probe may not achieve its target depth or monitoring period, this study investigates how the depth (2-5. m), duration (0-1 Martian year) and quality of measurements influence the accuracy of planetary heat flow. An inverse model is used to show that, in the preceding scenarios, the accuracy of planetary heat flow directly estimated from depth-dependent thermal conductivity with 10-20% precision errors, temperatures with 50-100. mK precision errors and modelling uncertainties up to 500. mK, can, on average, be improved by a factor of 27 with optimization to 13%. Accuracies increase with sensor penetration depth and regolith monitoring period. Heat flow optimized from instantaneous measurements or those with the shortest regolith monitoring periods have increased accuracy where the frequency and amplitude of the temperature variation are lowest. The inverse model is based on the Function Specification Inversion method. This study demonstrates that a solution subspace can be identified within a space of uncertainties modelled for the temperature measurements and planetary heat flow: the subspace is defined by a constant log-ratio of their respective standard deviations. Optimized heat flow estimates display reduced correlation with increasing temperature precision and systematic conductivity errors, with the constraint of other known model parameters. Consequently, the model permits upper bounds to be placed on the conductivity estimate without conductivity optimization, as heat flows are optimized to a limiting value with increasing systematic conductivity errors for any given parameter set. Overall, the results demonstrate a 52% chance of achieving a direct heat flow estimate accurate to within 40%, with the same being 82% after optimization.
Returning to the Moon has been advocated by a number of planetary scientists in order to answer several key scientific questions. The UK has an active lunar science community keen to support (robotic) lunar exploration. However, for several years, these interests have been eclipsed by the drive to Mars. Recently there is a renewed global interest in the Moon, demonstrated by the Vision for Space Exploration in the USA, the evolving Global Exploration Partnership, and new lunar missions from Europe, Japan, China and India. The ESA Aurora programme may also broaden its focus to embrace the Moon as well as Mars - realising that many of the major technical challenges that are faced by Mars missions could be de-risked by relatively inexpensive and timely lunar precursors. Surrey Satellite Technology Ltd. (SSTL) and Surrey Space Centre (SSC) have been preparing a 'smallsat' approach to achieving a low-cost lunar mission for more than a decade - including various activities, such as Phase B study of LunarSat funded by ESA and a current hardware contribution to the Chandrayaan-1 mission. With the recent successes in GIOVE-A, TOPSAT & BEIJING-1, alongside participation in Aurora & Chandrayaan-1, Surrey has developed capabilities for providing affordable engineering solutions to space exploration. In 2006, SSTL/SSC was funded by the UK Particle Physics and Astronomy Research Council (PPARC) (now included within the UK Science & Technology Facilities Council) to undertake a study on low-cost lunar mission concepts that could address key scientific questions. This paper presents some major results from this study (Phipps and Gao, 2006) and provides preliminary definitions of two down-selected mission proposals.
The Heat flow and Physical Properties Package (HP3) is a set of sensors used for the in-situ measurement of the planetary surface heat flow on Mercury or other terrestrial planets. The system is designed to operate underground, down to five meters deep. The aim of this study is to find out and minimize the disturbances that the system produces on the measurement of the heat flow. The dedicated thermal model includes all hardware components and the soil, with a complex dynamic connection to simulate the relative motion of the probe in the soil during the penetration. This allows to analyze the phase in which the system reaches its final depth and creates the biggest disturbances by injecting waste heat into the soil. In addition to modeling, an experiment was carried out to determine the thermal contact conductance between payload compartment and borehole surface. Since the thermal interactions between a granular medium and solid materials in a vacuum environment (or in rarefied atmosphere) need to be analyzed in detail, this first quantification is of certain interest.
The exploration of space has been at the forefront of scientific thought anddiscovery for the last half century. Beginning with the first Sputnik satellite in 1957 to the Curiosity landing and the other numerous ongoing missions of today, mankindis setting its sights away from Earth.
Planetary heat flow measurements are made with a series of high-precision temperature sensors deployed in a column of regolith to determine the geothermal gradient. Such sensors may, however, be susceptible to other influences, especially on worlds with atmospheres. First, pressure fluctuations at the surface may pump air in and out of pore space leading to observable, and otherwise unexpected, temperature fluctuations at depth. Such pumping is important in subsurface radon and methane transport on Earth: evidence of such pumping may inform understanding of methane or water vapor transport on Mars. Second, the subsurface profile contains a muted record of surface temperature history, and such measurements on other worlds may help constrain the extent to which Earth's Little Ice Age was directly solar-forced, versus volcanic-driven and/or amplified by climate feedbacks.
Proc. IMAPS pp. 271-276 preprint manuscript 1-10
The paper describes technology of manufacturing and preliminary test results of the experimental design of thin film resistors dedicated to thermometric sensing and micro heating. The resistors are designed for a use in the instrument called penetrator to perform the Multi Purpose Sensor (MUPUS) package of space experiments provided by University of Muenster in the frame of the ESA Cornerstone Mission ROSETTA. The instrument will be stuck in the nucleus body of the comet Wirtanen in 2011 to investigate in-situ thermal properties of icy material in a body of a cometary nucleus. The layout of thermometric sensors employs thin film Titanium resistors which are buried inside a wall of a ~35cm long cylindrical multilayered structure of a kapton foil substrate.
Reliable measurements of the Moon's global heat flow would serve as an important diagnostic test for models of lunar thermal evolution and would also help to constrain the Moon's bulk abundance of radioactive elements and its differentiation history. The two existing measurements of lunar heat flow are unlikely to be representative of the global heat flow. For these reasons, obtaining additional heat flow measurements has been recognized as a high priority lunar science objective. In making such measurements, it is essential that the design and deployment of the heat flow probe and of the parent spacecraft do not inadvertently modify the near-surface thermal structure of the lunar regolith and thus perturb the measured heat flow. One type of spacecraft-related perturbation is the shadow cast by the spacecraft and by thermal blankets on some instruments. The thermal effects of these shadows propagate by conduction both downward and outward from the spacecraft into the lunar regolith. Shadows cast by the spacecraft superstructure move over the surface with time and only perturb the regolith temperature in the upper 0.8m. Permanent shadows, such as from thermal blankets covering a seismometer or other instruments, can modify the temperature to greater depth. Finite element simulations using measured values of the thermal diffusivity of lunar regolith show that the limiting factor for temperature perturbations is the need to measure the annual thermal wave for 2 or more years to measure the thermal diffusivity. The error induced by permanent spacecraft thermal shadows can be kept below 8% of the annual wave amplitude at 1m depth if the heat flow probe is deployed at least 2.5m away from any permanent spacecraft shadow. Deploying the heat flow probe 2m from permanent shadows permits measuring the annual thermal wave for only one year and should be considered the science floor for a heat flow experiment on the Moon. One way to meet this separation requirement would be to deploy the heat flow and seismology experiments on opposite sides of the spacecraft. This result should be incorporated in the design of future lunar geophysics spacecraft experiments. Differences in the thermal environments of the Moon and Mars result in less restrictive separation requirements for heat flow experiments on Mars.
Regolith and dust cover the surfaces of the Solar Systems solid bodies, and thus constitute the visible surface of these objects. The topmost layers also interact with space or the atmosphere in the case of Mars, Venus and Titan. Surface probes have been proposed, studied and flown to some of these worlds. Landers and some of the mechanisms they carry, e.g. sampling devices, drills and subsurface probes (“moles”) will interact with the porous surface layer. The absence of true extraterrestrial test materials in ample quantities restricts experiments to the use of soil or regolith analogue materials. Several standardized soil simulants have been developed and produced and are commonly used for a variety of laboratory experiments. In this paper we intend to give an overview of some of the most important soil simulants, and describe experiments (penetrometry, thermal conductivity, aeolian transport, goniometry, spectroscopy and exobiology) made in various European laboratory facilities.
We investigate the influence of the external temperature forcing given
by seasonal, interannual, and climatic temperature changes on the
surface heat flow of Mars and determine how meaningful measurements of
the internal planetary heat flow can be obtained. The influence of
seasonal temperature changes is found to be efficiently removed if
measurements are extended over the period of at least a full Martian
year. Interannual variability due to, e.g., eolian-driven surface albedo
changes typically alters the heat flow by less than 15%, although errors
may be larger if the soil's thermal conductivity and the albedo
variations are both large. Heat flow perturbations caused by long-term
climatic changes are found to stay below 15%. In order to also determine
the soil's thermal conductivity with an accuracy of 20% or better, a
direct conductivity measurement is required. We conclude that a
measurement of the Martian planetary heat flow is possible with an
accuracy of 30% or better if measurements are extended over the period
of at least a full Martian year and thermal conductivity is directly
measured. Temperature sensors should have a precision of 0.1 K, and
measurements should be conducted up to a depth of 3-5 m.
In recent years the exploration of planetary bodies by surface probes has entered a new phase of interest. The mechanical properties of the near-surface layers of cometary and planetary bodies, including their strength, texture and layering, are important parameters needed both for a proper physical understanding of these bodies and for the design of lander missions.The strength properties of such a surface can be determined either by measuring the penetration resistance encountered by a slowly penetrating tip (quasi-static penetrometry), or by impacting the surface with an artificial body whose mechanical properties and impact velocity are known. At low speeds (up to about 300 m s−1), it is often feasible to measure the force or deceleration during penetration (‘impact’ or ‘dynamic’ penetrometry). If the event is better described in terms of hypervelocity impact cratering than penetration, analysis of the resulting crater is performed instead. Other uses of artificial impacts include the generation of seismic waves to aid the calibration of seismometers and the formation of a crater and / or ejecta for analysis or sampling of the target body. Such methods feature in many recent, current and forthcoming planetary missions. Examples include: the Surface Science Package of the Huygens probe, the anchoring harpoon of the Rosetta Lander, various Mars penetrators and landers, NASA's Deep Impact mission and ESA's planned Mercury cornerstone mission BepiColombo.A short overview of missions (past, present, future) featuring penetrometry experiments or artificial impacts is given. The theory of impact penetration and methods to interpret deceleration profiles in terms of material strength are discussed and applied to data sets obtained from test shots performed with the Rosetta Lander anchoring harpoon.
A measurement of the martian planetary heat flow requires the determination of the subsurface temperature gradient, which is affected by surface insolation. I investigate the propagation of thermal disturbances caused by lander shadowing and derive measurement requirements for in situ heat flow experiments. I find that for short term measurements spanning 180 sol, a measurement depth of at least 2 m is needed to guarantee a stable thermal environment directly underneath the lander for Moon-like thermal conductivities of . For extremely large conductivities of , this depth needs to be increased to 4 m, but if the probe can be deployed outside the lander structure, the respective depths can be decreased by 1 m. For long term measurements spanning at least a full martian year heat flow perturbations are smaller than 5% below a depth of 3 m directly underneath the lander. Outside the lander structure, essentially unperturbed measurements may be conducted at depths of 0.5 and 1.5 m for thermal conductivities of 0.02 and , respectively.
As the inner end-member of the planetary system, Mercury plays an important role in constraining and testing dynamical and compositional theories of planetary formation. With its companions Venus, Earth and Mars, it forms the family of terrestrial planets, a category of celestial objects in which each member holds information essential for retracing the history of the whole group. For example, knowledge about the origin and evolution of these planets is one of the keys to understanding how conditions to support life have been met in the Solar System and, possibly, elsewhere. This quest is all the more important as terrestrial-like objects orbiting other stars are not yet accessible; our own solar system remains the only laboratory where we can test models that are also applicable to other planetary systems. The exploration of Mercury is therefore of fundamental importance for answering questions of astrophysical and philosophical significance, such as: ‘Are terrestrial bodies a common feature of most planetary systems in the Galaxy?’
Space weathering is now generally accepted to modify the optical and magnetic properties of airless planetary regoliths such as those on the Moon and Mercury. Under micrometeorite and ion bombardment, ferrous iron in such surfaces is reduced to metallic iron spheres, found in amorphous coatings on almost all exposed regolith grains. The size and number distribution of these particles and their location in the regolith all determine the nature and extent of the optical and magnetic changes. These parameters in turn reflect the formation mechanisms, temperatures, and durations involved in the evolution of the regolith. Studying them in situ is of intrinsic value to understanding the weathering process, and useful for determining the maturity of the regolith and providing supporting data for interpreting remotely sensed mineralogy. Fine-grained metallic iron has a number of properties that make it amenable to magnetic techniques, of which magnetic susceptibility is the simplest and most robust. The magnetic properties of the lunar regolith and laboratory regolith analogues are therefore reviewed and the theoretical basis for the frequency dependence of magnetic susceptibility presented. Proposed here is then an instrument concept using multi-frequency measurements of magnetic susceptibility to confirm the presence of fine-grained magnetic material and attempt to infer its quantity and size distribution. Such an instrument would be invaluable on a future mission to an asteroid, the Moon, Mercury or other airless rocky Solar System body.
The space mission Rosetta undertaken by the European Space Agency (ESA) is encountered to approach the comet P/Wirtanen, land on it and perform in-situ investigations. The mission contains one of many experiments - the Multi Purpose Sensor (MUPUS) package of space experiments provided by the Institute of Planetology, University of Muenster, Germany.
Proc. IMAPS pp. 271-276 preprint manuscript 1-10
The paper describes technology of manufacturing and preliminary test results of the experimental design of thin film resistors dedicated to thermometric sensing and micro heating. The resistors are designed for a use in the instrument called penetrator to perform the Multi Purpose Sensor (MUPUS) package of space experiments provided by University of Muenster in the frame of the ESA Cornerstone Mission ROSETTA. The instrument will be stuck in the nucleus body of the comet Wirtanen in 2011 to investigate in-situ thermal properties of icy material in a body of a cometary nucleus. The layout of thermometric sensors employs thin film Titanium resistors which are buried inside a wall of a ~35cm long cylindrical multilayered structure of a kapton foil substrate.
Discussion of the thermal conductivity of particulate materials is dispersed over several decades and a wide range of disciplines. In addition, there is some disparity among the reported values. This paper presents a review of the methodology available for the study of thermal conductivity of particulate materials, with an emphasis on low atmospheric pressures, and an assessment of the dependability of the data previously reported. Both steady state and nonsteady state methods of thermal conductivity measurement are reviewed, delineating the advantages, disadvantages, and sources of error for each. Nonsteady state methods generally are simpler and more efficient. The transient hot wire and differentiated line-heat source are the preferred methods for the laboratory. These methods are better suited for small samples and short measurement times and are therefore the best methods to use for a series of comprehensive studies. Results of previous studies are presented, compared, and evaluated. A good way to assess the relative accuracy is to compare the values of thermal conductivity versus atmospheric pressure obtained from several experimenters. The lowest values of thermal conductivity at vacuum and very low atmospheric pressure, and the steepest slopes on the thermal conductivity versus atmospheric pressure curves, are indicative of the most accurate data. Previous thermal conductivity studies have shown that the thermal conductivity of particulate materials increases with increasing atmospheric pressure, with increasing particle size, and with increasing bulk density of the material. At vacuum, the thermal conductivity of particulate materials is proportional to the cube of the temperature. The temperature dependence of thermal conductivity is much less obvious at higher atmospheric pressures.
Thermal conductivities were measured with a line-heat source for three particulate materials with different particle shapes under low pressures of a carbon dioxide atmosphere and various bulk densities. Less than 2 mum kaolinite exhibited a general decrease in thermal conductivity with increasing bulk density. For the range of atmospheric pressures appropriate for Mars, a reduction in porosity of 24% decreased the thermal conductivity by 24%. Kaolinite manifests considerable anisotropy with respect to thermal conductivity. As the particles align the bulk thermal conductivity measured increasingly reflects the thermal conductivity of the short axis. When kyanite is crushed, it forms blady particles that will also tend to align with increasing bulk density. Without any intrinsic anisotropy, however, kyanite particles, like other particulates exhibit an increase in thermal conductivity with increasing bulk density. Under Martian atmospheric pressures, a reduction in porosity of 30% produces a 30% increase in thermal conductivity. Diatomaceous earth maintains a very low bulk density due to the highly irregular shape of the individual particles. A decrease in porosity of 17% produces an increase in thermal conductivity of 27%. The trends in thermal conductivity with bulk density, whether increasing or decreasing, are often not smooth. Whether oscillations in the trends presented in this paper and elsewhere have any physical significance or whether they are merely artifacts of the precision error is unclear. Clarification of this question may not be possible without higher-precision measurements from future laboratories and further development of theoretical modeling.
A line-heat source apparatus was assembled for the purpose of measuring
thermal conductivities of particulate samples under low pressures of a
carbon dioxide atmosphere. The primary result of this project is the
compilation of the first comprehensive suite of measurements of the
dependence of thermal conductivity on particle size. The thermal
conductivity increases with increasing particle size and atmospheric
pressure. In particular, over the range of Martian atmospheric
pressures, from 1 to 7 torr, the thermal conductivity was found to be
empirically related to approximately the square root of the particle
diameter and the square of the cubed root of the atmospheric pressure.
At the average pressure of the Martian surface (6 torr) the thermal
conductivity varies from 0.011 W/mK, for particles less than 11 μm in
diameter, to 0.11 W/mK, for particles 900 μm in diameter. These
results differ significantly from the particle size dependence estimated
for Mars from previous measurements, except for 200-μm particles,
whose thermal conductivity is 0.053 W/mK. The thermal conductivities of
larger particles are lower than the previous estimate, by 40% at 900
μm, and the thermal conductivities of smaller particles are higher
than the previous estimate, by 60% at 11 μm. These newer estimates
agree with other lines of evidence from Martian atmospheric and
surficial processes and lead to improved particle size estimates for
most of the planet's surface.
Thermal history of Mercury's interior is examined using the model of Stevenson et al. (1983), extended to include the effects of tidal heating in Mercury's solid inner core. The implications of Mercury's thermal history for the source of the planet's magnetic field are discussed. It is shown that the major results of this model are similar to the results obtained with the Stevenson et al. model, except for the addition of inner-core tidal dissipation. It is concluded that the extended model properly characterizes Mercury's internal structure and thermal history, and that the criteria for dynamo generation are not properly satisfied. Alternative explanations, including the possibility of a weak thermoelectric dynamo, are examined.
As the inner end-member of the planetary system, Mercury plays an important role in constraining and testing dynamical and compositional theories of planetary formation. With its companions Venus, Earth and Mars, it forms the family of terrestrial planets, a category of celestial object where each member holds information essential for retracing the history of the whole group. For example, knowledge about the origin and evolution of these planets is one of the keys to understanding how conditions to support life have been met in the Solar System and, possibly, elsewhere. This quest is all the more important as terrestrial-like objects orbiting other stars are not accessible; our own environment remains the only laboratory where we can test models that are also applicable to other planetary systems. The exploration of Mercury is therefore of fundamental importance for answering questions of astrophysical and philosophical significance, such as: 'Are terrestrial bodies a common feature of most planetary systems in the Galaxy?'.
Owing to the low surface gravity of the Rosetta target comet 46P/Wirtanen, a means of anchoring the Rosetta Lander to the cometary surface will be necessary. This task can be accomplished by firing an anchor into the cometary soil immediately after touchdown to prevent a rebound of the spacecraft from the surface or subsequent ejection by other forces, and to allow for mechanical activities (drilling, etc.) at the landing site.The rationale for anchoring is examined, based on estimates of the main forces likely to act on the spacecraft after landing. We report on the development of an anchoring device using a pyrotechnic gas generator as a power source and an instrumented anchor.In addition to the anchoring function, which is the primary purpose of this system, the integration of acceleration and temperature sensors into the tip offers the possibility to determine some important material properties of the cometary surface layer. The accelerometer is designed to measure the deceleration history of the projectile and is thus expected to give information on how the material properties (in particular strength) change within the penetrated layer(s), while the temperature sensor will measure temperature variations at the depth at which the anchor finally comes to rest. As the mechanical properties of the material are not known, it is difficult to predict the final depth of the anchor with any great certainty, but it may well be greater than that reached by any other of the lander's instruments.The instrumented anchor will be part of the MUPUS experiment, selected to form part of the Rosetta Lander payload. We report on results of laboratory simulations of anchor penetration performed at the Institut für Weltraumforschung, Graz, and compare these with models of projectile penetration. The value of the results expected from the penetrometry experiment in the context of an improved understanding of cometary processes is discussed.
We present images of Mercury's thermal emission that were obtained with the Berkeley-Maryland-Illinois Array (BIMA) millimeter interferometer at a wavelength of 0.3 cm and with the VLA (Very Large Array) at wavelengths from 1.3 to 20.5 cm. These images are analyzed with detailed thermophysical and radiative transfer models that are based in part on a lunar analogy. We constrain the thermophysical model with Mariner 10 infrared measurements of Mercury's night-side surface temperature and show that Mercury's regolith, like that of the Moon, consists of a thermally insulating surface layer, with a thickness of a few centimeters, atop a highly compacted region that extends to a depth of several meters. The radiative transfer model is constrained in part by linear polarization images that we obtained with the VLA at wavelengths from 2.0 to 20.5 cm. These images reveal wavelength-dependent scattering at the surface boundary and rms surface slopes that range from 15 deg at lambda 2.0 cm to 10 deg at lambda 6.2 cm. We develop a method for constraining the microwave opacity at each wavelength by modeling diurnal brightness variations over the resolved disk and find that Mercury's regolith is at least two to three times more transparent than the lunar maria and at least 40% more transparent than the lunar highlands. This difference is likely due to lower Fe and Ti abundances in Mercury's regolith, which is consistent with Mercury's high visual albedo and suggests that most of Mercury's surface is an extreme example of the lunar highlands.
The new algorithm of the thermal conductivity and thermal diffusivity determination from the transient hot-wire method has been applied to measurements performed in several solid materials. The algorithm makes use of the exact formula for the temperature variations, instead of its simple, asymptotic form that has been employed earlier. In the process of the least-square optimization of the residual function three parameters are obtained; thermal conductivity, thermal diffusivity, and the initial temperature. Two different variants of the method are presented: the classical one with the power kept constant during the measurements and the newly introduced constant current technique. The latter one has an advantage of requiring simpler conditioning electronics, and can therefore be recommended in space applications. The results of data processing show that thermal conductivity can be reliably determined even from the nonasymptotic part of the temperature measurements. The determination of thermal diffusivity is more difficult and requires high quality temperature data from the whole measurement interval. © 1997 American Institute of Physics.
This book is an English translation of the Russian original
"Kosmokhimicheskie issledovaniia planet i sputnikov" published in 1985.
It describes the methods, instrumentation and experimental results which
have already been used or which will be used by space vehicles for
exploring the composition, structure and properties of extraterrestrial
material, on the basis of which modern concepts of the planets and
planetary satellites have been developed. Contents: Part I. Modern
concepts of planets and satellites. 1. Origin and evolution of the
solar system. 2. Mercury. 3. Venus. 4. Mars. 5. Planetary satellites.
Part II. Exploration of planets and satellites by space vehicles. 1.
Gamma-ray spectrometric studies. 2. X-ray spectrometric studies. 3.
Neutronmetry. 4. Alpha-spectrometry. 5. Mass-spectrometric studies. 6.
The exploration of Mars and Phobos (Phobos mission). 7. First results of
gamma-ray measurements of Mars from Phobos 2 spacecraft.
The recently upgraded Arecibo S-band (λ12.6-cm) radar was used to make delay-Doppler images of Mercury's north polar region, where earlier observations had shown strong echoes from putative ice deposits in craters. The image resolution of 1.5–3 km is a sub-stantial improvement over the 15-km resolution of the older Arecibo images (J. K. Harmon et al. 1994, Nature 369, 213–215). The new observations confirm all the original polar features and reveal many additional features, including several at latitudes as low as 72–75 • N and several from craters less than 10 km in diameter. All of the new features located on the Mariner-imaged side of the planet can be matched with known craters or other shaded areas. We find the north pole to be located 65 km from the original Mariner-based pole and 15 km from the new Mariner-based pole of M. S. Robinson et al. (1999, J. Geophys. Res. 104, 30,847–30,852). The improved resolution reveals fine structure in the radar features and their re-spective host craters, including radar shadowing/highlighting by central peaks and rim walls, rim terracing, and preferential con-centration of radar-bright deposits in shaded southern floor areas. The radar features' high brightness, circular polarization inversion (µ c = 1.25), and confinement to regions permanently shaded from direct sunlight are all consistent with volume scattering from a cold-trapped volatile such as clean water ice. The sizes and locations of most of the features show good agreement with the thermal model of A. R. Vasavada, D. A. Paige, and S. E. Wood (1999, Icarus 141, 179–193) for insulated (buried) water ice, although the problems of explaining radar features in small craters and the rapid burial required at lower latitudes suggest that other factors may be sup-pressing ice loss after emplacement.
Means for sub-surface investigations are of great interest for the exploration of planetary bodies such as the Moon, Mars and comets, in the future scenarios intending to send probes on their surface. To this aim, in-depth penetration may be performed either by drilling or by self-propelled devices To reach depth of several meters in loose to hard compact soil, self-propulsion has a great advantage of simplicity over drilling, as it does not require the complex autonomous assembly of several drill sections. The mobile penetrometer presented here is an original device of this category. This penetrometer is a slender cylinder of small mass, which can penetrate as a mole - slowly, but surely! - loose to compact regolith soils at great depth. It is actuated by a fully enclosed motorised shock mechanism, powered through a tethered cable. The cable length is the practical limit to its penetration depth. Once a fraction of its length is inserted in the soil - which requires the application of a small external force - it may freely progress, during ground tests, vertically downwards up to horizontally, which demonstrates its applicability in reduced and micro-gravity environment. As payload, this exploration device may carry various sensors, for instance thermal, seismic, optical, or a camera lens. It may be implemented with in-situ analysis devices, or be used to take and retrieve samples at various depths. The current prototype has a diameter of 1.9 cm, length 32.5 cm, a mass 0.4 kg, and an average power consumption of 2 W (max. 5 W) Further size and mass reduction to diameter 1.3 cm, length 25 cm and 0.25 kg are feasible. An approximately equivalent mass is estimated for the penetrometer support and release system, which shall maintain it at start of penetration. The paper will detail the design of the essential item, the inner shock echanism, and its adaptation to the severe tribology requirements of low temperature and vacuum. The results of the testing, in sand and other model soils, at ambient and in TV chamber, are presented. The principle of this mobile penetrometer has been invented and patented by the Russian Mobile Vehicle Engineering Institute (VNIITRANSMASH) in St. Petersburg, which has already built a large size functional prototype. They perform its miniaturisation and spatialisation for the requirements of cometary, Moon and Mars environment in the frame of an ESA study led by Tecnospazio, in which DLR is responsible for testing.
The problem of determining the effective thermal conductivity of a two‐phase system, given the conductivities and volume fractions of the components, is examined. Equations are described which have been proposed as solutions to this problem, including those of Maxwell, de Vries, and Kunii and Smith, the weighted geometric mean equation, and an equation based on a three‐element resistor model found applicable to the analogous electrical conductivity problem. Experimental results are presented for five unconsolidated samples: three quartz sand packs, a glass bead pack, and a lead shot pack. The method of conductivity measurement using the transient line heat source (thermal conductivity probe) is described. Data are reported showing the variation of effective thermal conductivity with porosity, solid particle conductivity, saturating fluid conductivity, and the pressure of the saturating gas. From considerations based on the kinetic theory of gases, it is shown that the characteristic dimension of the pore space, with respect to heat conduction in the gas occupying this space, is smaller than the mean particle diameter by a factor of roughly 100. The thermal conductivity equations which best represent the observed data are those of de Vries, and Kunii and Smith, and a slightly modified version of the resistor model equation.
Of the terrestrial planets, Earth and probably Mercury possess substantial intrinsic magnetic fields generated by core dynamos, while Venus and Mars apparently lack such fields. Thermal histories are calculated for these planets and are found to admit several possible present states, including those which suggest simple explanations for the observations; whule the cores of Earth and Mercury are continuing to freeze, the cores of Venus and Mars may still be completely liquid. The models assume whole mantle convection, which is parameterized by a simple Nusselt-Rayleigh number relation and dictates the rate at which heat escapes from the core. It is found that completely fluid cores, devoid of intrinsic heat sources, are not likely to sustain thermal convection for the age of the solar system but cool to a subadiabatic, conductive state that can not maintain a dynamo. Planets which nucleate an inner core continue to sustain a dynamo because of the gravitational energy release and chemically driven convection that accompany inner core growth. The absence of a significant inner core can arise in Venus because of its slightly higher temperature and lower central pressure relative to Earth, while a Martian core avoids the onset of freezing if the abundance of sulfur in the core is ⪆15% by mass. All of the models presented assume that (I) core dynamos are driven by thermal and/or chemical convection; (ii) radiogenic heat production is confined to the mantle; (iii) mantle and core cool from initially hot states which are at the solidus and superliquidus, respectively; and (iv) any inner core excludes the light alloying material (sulfur or oxygen) which then mixes uniformly upward through the outer core. The models include realistic pressure and composition-dependent freezing curves for the core, and material parameters are chosen so that the correct present-day values of heat outflow, upper mantle temperature and viscosity, and inner core radius are obtained for the earth. It is found that Venus and Mars may have once had dynamos maintained by thermal convection alone. Earth may have had a completely fluid core and a dynamo maintained by thermal convection for the first 2 to 3 by, but an inner core nucleates and the dynamo energetics are subsequently dominated by gravitational energy release. Complete freezing of the Mercurian core is prohibited if it contains even a small amount of sulfur, and a dynamo can be maintained by chemical convection in a thin, fluid shell.
The BepiColombo mission is planned to very accurately measure the gravity field, the topography, and the tidal Love numbers of Mercury. In this paper, we review our present knowledge of the interior structure and show how the data from BepiColombo can be used to improve on our knowledge. We show that our present estimates of the core mass and volume depend mostly on our confidence in cosmochemically constrained values of the average silicate shell and core densities. The moment of inertia (MOI) C about the rotation axis will be determined very accurately from the degree 2 components of the gravity field and from measurements of the obliquity and the libration frequency of the rotation axis. The ratio Cm/C between the MOI of the solid planet to the MOI of the planet, both about the rotation axis, will additionally be obtained. If the core is liquid or if there is a liquid outer core, Cm/C will be around 0.5. In this case, Cm can be identified with the MOI of the silicate shell. If the core is solid, Cm/C will be about 1. The MOI C can be used to test and refine present models but will most likely not per se help to increase the confidence in the two-layer model beyond the present level, at least if there is a substantial inner core. C and Cm/C can be used to calculate the inner core radius and the outer core density, assuming the silicate shell density and the inner core density are given by cosmochemistry. The accuracy of the outer core density estimate depends largely on the confidence in the cosmochemical data. The inner core radius can be determined to the accuracy of the densities if the inner core radius is greater than 0.5 core radii. These values can be checked against the Love number of the planet. The higher order components of the gravity field can be used to estimate core–mantle boundary undulations and crust thickness variations. The former will dominate the gravity field at long wavelength, while the latter will dominate at short wavelengths.
The first — and possibly deepest — in situ science measurements on the 46P/Wirtanen nucleus will be made by two sensors of the Rosetta Lander's MUPUS experiment. A piezoelectric shock accelerometer (ANC-M) and a resistance temperature sensor (ANC-T) will be mounted in the Lander's harpoon anchor. This will be shot into the surface at about on touchdown, reaching a final depth of between a few centimetres and about 2.5 m, depending on the hardness of the ground and the maximum available cable length. Early indications of the strength of the surface material and any distinct layers should prove valuable to subsequent depth-sensitive investigations, including the MUPUS thermal probe, seismic sounding experiments, the sampling drill and composition analyses of the extracted material. Interpretation of the ANC-M data will help to constrain models of the formation and evolution of the material found at the landing site and document the mechanical and structural context of nearby sampled material. We report on the results of recent test shots performed with a prototype anchor into several porous materials: two types of glass foam, H2O ice and CO2 ice. With the help of data from direct shear tests and quasi-static penetration tests, we interpret the processed deceleration data using a cavity-expansion penetration model. Layers of distinctly different strengths can be detected and located, and the deceleration profiles are in reasonable agreement with the profiles obtained by quasi-static tests. The anchor projectile's long sharp tip tends to smear out the boundaries, however. In applying the penetration model we found that the coefficient of sliding friction and the target's volumetric strain have a much stronger influence on the deceleration profile than the initial target density and angle of internal friction. Very small values of volumetric strain (corresponding to high ‘drag coefficient’) were required to fit deceleration profiles to the measured data for the glass foam, contrary to what we initially expected by inspecting the thin layer of crushed material around the walls of the penetrated channel. We interpret this to mean that such brittle, porous materials as the glass foam (and perhaps highly porous, brittle, cryogenic ice) do not exhibit plastic deformation before failing completely by the crushing of cell walls. The decelerating forces are thus thought to be dominated by momentum transfer to the crushed material and by the crushing strength of the cellular microstructure, rather than by the force required to deform the target plastically. The cavity-expansion model seems to be well-suited to the ice shots, but for the brittle, cellular glass foam, alternative approaches, taking into account the material's microstructure, are needed. As a first step in this direction, a microstructural model linking textural properties of the material (pore and grain size, and relative contact area between grains) is applied to the glass foam data, obtained from quasi-static penetration tests and from direct shear strength tests. It is demonstrated that the dependence of strength on porosity can be well represented by the model suggested. A microstructural model for sintered ices, relating strength properties to porosity and thermal properties, would be useful for interpretation of MUPUS ANC-M data in the context of other physical properties measurements. The work presented here may also have some relevance to the design of future comet landers or penetrators. The harpoon anchor/penetrometer approach could be employed on other minor body landing missions, while the modelling technique is similar in many ways to that appropriate for other penetrometers/penetrators.
Measurements of the thermal conductivity of porous loose mineral, porous H2O ice and porous CO2 ice samples under low temperatures (77 K < T < 300 K) and pressures (10−4 Pa < p < 105 Pa) are reported. The samples were selected to cover the end members of possible comet nucleus compositions and the ambient conditions were chosen to investigate the samples under space conditions. A transient technique is used for the measurements which is well suited for in situ application. The method is based on the line heat-source technique: a thin internally heated cylindrical sensor is inserted into the sample material. The thermal conductivity is deduced from the observed temperature rise in the sensor and the heating power applied. Depending on sensor dimensions, single experiment runs may be completed within a few minutes. The method proved to be accurate, fast and well suited for an application in the laboratory as well as in situ, e.g. on future comet nucleus or Mars missions. A thermal probe (MUPUS-PEN) which employs the experimental technique discussed here has been proposed for the ROSETTA surface science package “RoLand”. The thermal conductivity of the loose dunite sample is studied as a function of gas pressure. At low pressures, it is almost constant and close to 0.03 W m−1 K−1. At atmospheric pressure, the thermal conductivity is about one order of magnitude higher. Both domains are linked by a pressure region with a strong pressure dependency of the thermal conductivity. Three porous water ice samples with different pore sizes have been investigated. The results are in agreement with theoretical predictions (e.g. Steiner et al., 1991) and reveal a strong increase of the thermal conductivity at temperatures close to the sublimation temperature of water ice (≈ 200 K in vacuo). The increase is due to heat transport by pore filling vapour which is more effective in samples with large pore radii. The measured matrix conductivity is close to 0.02 W m−1 K−1, while maximum values for the effective (= matrix + vapour) thermal conductivity at high temperatures exceed 0.25 W m−1 K−1. Similar results are obtained for one porous CO2 ice sample.
Thermal evolution models for the terrestrial planets Mars, Mercury, and Venus with core and mantle chemical differentiation, lithosphere growth, and volcanic heat transfer have been calculated. The mantle differentiates by forming a crust and the core differentiates by inner core solidification. Continued volcanic activity for billions-of-years is found to be possible even on small terrestrial planets if crust growth is limited by lithosphere growth during the early evolution. Later, crust formation may be limited by the declining vigor of mantle convection. The thicknesses of the crust and lithosphere are found to depend mainly on planet size, on the bulk concentration of radiogenic elements in the planet, and on the ratio between volcanic and conductive heat transfer through the lithosphere. Two end-member models have been calculated and the concentration of radiogenics in the planet has been varied. In the first model, heat transfer from the mantle to the surface occurs via heat conduction through the lithosphere, while in the second model, mantle heat is advected via volcanic vents. Geologic evidence for volcanism on Mars and Mercury for at least 3.5 Ga and up to 1 Ga, respectively, the absence of a magnetic field on Mars, and the presence of such a field on Mercury suggest that heat transfer in these planets was dominated by heat conduction through the lithosphere for most of their thermal history. The present crust of Mercury is estimated to be a few tens of kilometers thick and about 10% of the mantle initial inventory of heat sources is fractionated into the crust. The Martian crust may be 50–100 km thick, possibly constituting more than a third of the lithosphere. Volcanic heat piping may have been an important heat transfer mechanism on Venus and volcanic activity may continue to the present day. Venus may have a crust that may constitute almost the entire lithosphere but crustal thickness may be limited by the basalt-eclogite phase transformation to 60 to 80 km. It is estimated that the present mantles of Mars and Venus are similarly depleted of about 20 to 40% of their initial heat source inventory.
A Compton Backscatter Densitometer has been proposed for the RoLand probe in order to measure the bulk density of material near the surface of a comet nucleus. RoLand is to be deployed from a spacecraft in orbit around the target comet, as part of the international Rosetta mission. The basis for the use of this technique on RoLand is explained. Densitometers have been used twice before in planetary exploration, however the RoLand design aims to employ a lower energy radioisotope source so that a lightweight detection system can be used. Monte Carlo simulation of scattering and absorption in semi-infinite bulk materials has been used to investigate the design parameters, specifically the variation of backscattered count rate with density and composition. Results indicate that a density measurement can be made provided that the basis elemental composition of the material is known.
Literature data on the thermal conductivity of solid, porous, and powder rocks and minerals are reviewed. The line heat source and thermal conductivity probe methods for measurement of thermal conductivity of these materials are described. Experimental data on the effects of pressure from 10−10 Torr to atmospheric and temperatures from 100° to 400°K on the thermal conductivity of solid, porous, and powder rocks are reported. The results are discussed in terms of possible lunar surface materials.
The MUPUS experiment on the Rosetta Lander will measure thermal and mechanical properties as well as the bulk density of the cometary material at and just below the surface of the nucleus of comet 46P/Wirtanen. A profile of bulk density vs. depth will be obtained by measuring the attenuation of gamma rays emitted by a 137Cs source. Compton scattering is the dominant interaction process at this energy, the attenuation depending directly on the total number of electrons along the source–detector path. This in turn is approximately proportional to the column density. We report here on the design of the bulk density instrument and the results of related Monte Carlo simulations, laboratory tests and calculations of the instrument's performance. The 137Cs radioisotope source is mounted in the tip of the MUPUS thermal probe—a diameter rod, to be hammered into the surface of the nucleus to a depth of . Two cadmium zinc telluride (CZT) detectors mounted at the top of the probe will monitor the count rate of photons. Due to the statistics of photon counting, the integration time required to measure column density to a particular accuracy varies with depth as well as with bulk density. The required integration time is minimised for a material thickness equal to twice the exponential attenuation length. At shallower depths the required time rises due to the smaller fractional change in count rate with varying depth, while at greater depths the reduced count rate demands longer integration times. The former effect and the fact that the first of the source–detector path passes not through the comet but through the material of the probe, mean that the first density measurement cannot be made until the source has reached a depth of perhaps . The laboratory experiments indicate that at this depth an integration time no less than (falling to at full penetration) would be required to measure a bulk density of to 5% accuracy, assuming a source activity of (decayed from an initial ). Although solutions involving feedback of the measured bulk density into a time-budgeting algorithm are conceivable, a simple approach where equal time is spent per unit depth may be best, providing an accuracy in bulk density of around 5–20%, for slices and the expected range of parameters.
The thermal sensors on the penetrator of the MUPUS experiment package selected for the ESA Rosetta mission will enable us to determine the near-surface energy balance of the nucleus of comet P/Wirtanen by measuring the subsurface temperature profile and the thermal conductivity of the near-surface layers. Model calculations suggest that the penetrator itself will perturb the ambient temperature field such that the temperature profile will be smoothed if the thermal diffusivity of the nucleus is significantly smaller than that of the penetrator tube. It is possible, however, to calculate the undisturbed temperature profile from the data using a method based on a solution of the transient inverse heat conduction problem. Our model calculations show that a satisfactory estimate of the undisturbed temperature field can be obtained in comparatively little computing time by calculating the temperature distribution in the model volume from temperature histories at discrete points representing the penetrator temperature sensors
In the years 2011–2013 the ESA mission Rosetta will explore the short period comet 46P/Wirtanen. The aims of the mission include investigation of the physical and chemical properties of the cometary nucleus and also the evolutionary processes of comets. It is planned to land a small probe on the surface of the comet, carrying a multitude of sensors devoted to in situ investigation of the material at the landing site. On touchdown at the nucleus, an anchoring harpoon will be fired into the surface to avoid a rebound of the lander and to supply a reaction force against mechanical operations such as sample drilling or instrument platform motion. The anchor should also prevent an ejection of the lander due to gas drag from sublimating volatiles when the comet becomes more active closer to the Sun. In this paper, we report on the development of one of the sensors of the MUPUS instrument aboard the Rosetta Lander, the MUPUS ANC-M (mechanical properties) sensor. Its purpose is to measure the deceleration of the anchor harpoon during penetration into the cometary soil. First the test facilities at the Max-Planck-Institute for Extraterrestrial Physics in Garching, Germany, are briefly described. Subsequently, we analyse several accelerometer signals obtained from test shots into various target materials. A procedure for signal reduction is described and possible errors that may be superimposed on the true acceleration or deceleration of the anchor are discussed in depth, with emphasis on the occurrence of zero line offsets in the signals. Finally, the influence of high-frequency resonant oscillations of the anchor body on the signals is discussed and difficulties faced when trying to derive grain sizes of granular target materials are considered. It is concluded that with the sampling rates used in this and several other space experiments currently under way or under development a reasonable resolution of strength distribution in soil layers can be achieved, but conclusions concerning grain size distribution would probably demand much higher sampling rates.
Thesis (Ph. D.)--University of Kent at Canterbury, 1997.
Finite-difference models are used to study the effects of insulation by the megaregolith on lunar thermal evolution. Results indicate that the megaregolith has two important influences on heat flow: (1) Because the megaregolith is exceptionally thin in mare regions, heat passes more readily through them than through highland regions, and even flows laterally from the highland toward the mare. As a result, heat flow is exceptionally high along a boundary between highland and mare regions. (2) On a global scale, megaregolith insulation combined with lithosphere insulation causes slow cooling, which as a cumulative effect results in high present-day mantle temperatures and heat flow. Assuming that the global mean megaregolith thickness is 2 km, a heat flow of 12 mW/sq m is best matched by models with bulk moon U contents of 20-21 ng/g. Independent constraints on lunar internal temperatures derived from magnetic and tectonic data are best matched by models with about 14 ng/g U. Thus the bulk moon U content is roughly 17 ng/g. These results imply that the bulk moon contents of U, and related refractory lithophile elements such as Th, Al, Ca, etc., must be considerably lower than commonly assumed.
The 3.5- and 2-year subsurface temperature histories at the Apollo 15 and 17 heat-flow sites have been analyzed, and the results yield significantly lower thermal conductivity determinations than the results of previous short-term experiments. The thermal conductivity determined by probes at a depth of about 150 cm and 250 cm lies in the range 0.9-1.3 times 10 to the -4th W/cm K. On the basis of measurements of variations of surface thorium abundance and inferred crustal thicknesses, the average global heat flux is estimated to be about 1.8 microwatts/sq cm. This requires a uranium concentration of 46 ppb.
Lunar-A penetrator: Its science and instruments
- H Mizutani
- A Fujimura
- M Hayakawa
- S Tanaka
- H Shiraishi
Mizutani, H., Fujimura, A., Hayakawa, M., Tanaka, S., Shiraishi, H.,
2001. Lunar-A penetrator: Its science and instruments. In: K omle, N.I.,
Kargl, G., Ball, A.J., Lorenz, R.D. (Eds.), Penetrometry in the Solar
System. Austrian Academy of Sciences Press, Vienna, pp. 125-136.
Thermische Evolution des Planeten Merkur berechnet unter Anwendung verschiedener Viskosit atsgesetze
- V Conzelmann
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