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Simulated winds in the bottom layer of MarsWRF at Ls = 81.84° (Spike 5). The plotted data are an average over the six hours indicated by the time period on the upper left of each panel. Panels (a and b) show the regional circulation, from which one can identify southwesterly downslope winds along the topographic dichotomy from midnight to sunrise, and northeasterly upslope winds from noon to sunset. Panels (c and d) show the Gale crater circulation, from which one can identify downslope winds along the inner wall of the crater rim and along Mount Sharp from midnight to sunrise, and upslope winds from noon to sunset. The crater circulation is well resolved by MarsWRF. Red colors show rising air. Blue colors show sinking air. Contours show surface elevation. Red stars mark the position of Curiosity.
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During its five years of operation as of 2017, the Sample Analysis at Mars (SAM) Tunable Laser Spectrometer (TLS) on board the Curiosity rover has detected six methane spikes above a low background abundance in Gale crater. The methane spikes are likely sourced by nearby emission from the surface. Here we use inverse Lagrangian modeling techniques...
Citations
... However, diurnal variations cannot explain the detection of either occasional methane spikes or seasonal methane variability. Recent modeling studies (Luo et al., 2021;Viudez-Moreiras et al., 2021) agree that reconciling TGO and TLS-SAM methane data requires some local, small, unknown sources of methane within the Gale crater. ...
... Without an extremely efficient unknown methane destruction mechanism, the released methane would have been detected by TGO, which scans all of the Martian atmosphere. The possibility that MSL just happened to land near the only active methane source on Mars is infinitesimal (Luo et al., 2021;Viudez-Moreiras et al., 2021). However, the Gale crater is unique because it is one of only two craters on Mars where a massive rover drives and drills the surface rocks. ...
Methane spikes observed in the Martian atmosphere require the abrupt release of large amounts of methane from the Martian subsurface. The mechanism for such release has not been identified. We tested whether gas traps can form under Mars‐like conditions in the shallow Martian regolith due to salt migration in the icy soil. Experiments were performed on various soil samples in a Mars Simulation Chamber comprising different perchlorate salts and water concentrations mixed with JSC Mars‐1A. Inside the chamber, the samples were exposed to a range of temperatures from −20°C to 10°C and maintained CO2 gaseous pressure between 8 and 10 mbars. As a methane analog, Neon was injected periodically underneath the soil sample. It was found that over a wide range of Mars‐like soil parameters, a gas impermeable soil seal can form over a relatively short period (3–13 days) but requires 5%–10% of perchlorate salt content in the soil. It was determined that such a seal could sustain several mbars of neon above the Martian atmospheric pressure in the soil. Based on our experiments, substantial amounts of gaseous methane may accumulate under the soil seal and get released abruptly into the atmosphere upon seal cracking. An abrupt release of methane from the shallow subsurface may help explain methane variability at the Martian surface, as the Mars Science Laboratory detected.
... Viúdez-Moreiras (2021a) suggested that the variability of winds in the vicinity of MSL is sufficient to produce strong methane spikes at MSL's general location from a nearby emission source, even without invoking sol-to-sol variability in winds, variable emission fluxes or eventual emissions into the atmosphere, or microscale flows not resolved in the meteorological data. A recent modeling study by Luo et al. (2021) also favors localized emission sources in the Gale Crater region. However, the background MSL observations of methane are even more complex in their interpretation. ...
The Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) Curiosity rover has detected both methane spikes and variable background methane abundance in recent years in Gale Crater, Mars. While methane spikes have been attributed to a hypothetical local or regional source emission, the background measurements acquired during the nighttime were postulated to represent the global methane abundance on Mars. However, recent high‐accuracy observations by instruments on the Trace Gas Orbiter (TGO) in several locations around the planet have not detected methane at all, apparently contradicting the SAM measurements. This paper analyzes the constraints that TGO and MSL impose on the hypothetical location of the emission source of methane responsible for the levels detected by SAM. The numerical simulations presented here indicate that not only the spikes but also the background measurements performed by MSL must result from localized emissions, specifically in the northwest interior of Gale Crater. Other simulated emission source locations at a greater distance from MSL, even if still within Gale Crater, are difficult to reconcile with current observations by MSL and TGO. Confirming previous studies, these results therefore point either to an improbable scenario, in which the rover has landed close to one of only a few localized emission sources on Mars, or to a problematic scenario, in which an unknown loss mechanism must be invoked that is able to destroy methane orders of magnitude faster than predicted by standard gas chemistry or to a weighted action between both scenarios.
A review of the studies on planetary atmospheres performed by Russian scientists in 2019–2022 prepared in the Commission on planetary atmospheres of the National Geophysical Committee for the National Report on Meteorology and Atmospheric Science to the 28 General Assembly of the International Union of Geodesy and Geophysics in Berlin, July 11–20, 2023, is presented.
The rapid loss of methane in Mars’ atmosphere observed recently by the Curiosity rover can be due to dehydrogenation by iron-oxide clusters/particles.
In recent years, the Tunable Laser Spectrometer within the Sample Analysis at Mars (TLS‐SAM) instrument on board the Mars Science Laboratory (MSL) Curiosity rover has detected methane variations in the atmosphere at Gale crater. Methane concentrations appear to fluctuate seasonally as well as sub‐diurnally, which is difficult to reconcile with an as‐yet‐unknown transport mechanism delivering the gas from underground to the atmosphere. To potentially explain the fluctuations, we consider barometrically induced transport of methane from an underground source to the surface, modulated by temperature‐dependent adsorption. The subsurface fractured‐rock seepage model is coupled to a simplified 1‐D atmospheric mixing model to provide insights on the pattern of atmospheric methane concentrations in response to transient surface methane emissions, as well as to predict sub‐diurnal variation in methane abundance for the northern summer period, which is a candidate time frame for a MSL Curiosity sampling campaign. Our analysis suggests that there is a lower limit to the subsurface fracture density that can produce the observed methane patterns, below which the atmospheric methane variations would be out of phase with the observations. The best‐performing model scenarios indicate a significant, short‐lived methane pulse just prior to sunrise, the detection of which by TLS‐SAM would be a potential indicator of the contribution of barometric pumping to Mars' atmospheric methane variations.
Measurements of atmospheric methane by the Curiosity rover's SAM-TLS instrument are providing evidence of seasonality with bimodal peaks in concentration. Given methane's short atmospheric lifetime relative to geological timescales, its presence implies a replenishing source, and the observed seasonality demands the proposition of a modulation mechanism. This paper focuses on the modulation mechanism. Our modeling study shows that barometric pumping driven by seasonal variation of atmospheric pressure, along with adsorption and desorption of methane in the shallow subsurface driven by temperature change, can explain the observed bimodal peaks in the seasonal variations of methane concentration. In the model, an active, continuous, steady-state deep source of methane is assumed, and carbon dioxide serves as the carrier gas for producing seasonal variation in the upper part of the sedimentary column for methane and other possible trace gaseous constituents. Our work also presents a comprehensive flow chart for modeling the microseepage of methane on Mars from first principles.
The absence of significant detectable signatures of organic molecules in the atmosphere and on the surface of Mars is a major unsolved puzzle. One possible explanation is that perchlorate-rich Martian soils, activated by solar ultraviolet (UV) radiation, create an environment favorable for the rapid oxidation of organics such as alkanes (including methane or CH4). In this paper, we measured product formation rates from the methane-perchlorate-UV system at room temperature. Our results show that magnesium perchlorate (Mg(ClO4)2•6H2O) surfaces exposed to UV light at wavelengths reaching the Mars' surface accelerate the decomposition of methane (CH4), resulting in the formation of carbon dioxide (CO2), carbon monoxide (CO), and volatile chlorine oxides. The production rates for CO2 and CO on UV-activated perchlorate surfaces are 2.5 and 4.5 times higher, respectively, than in the absence of perchlorate. In addition, with UV radiation exposure, perchlorate (ClO4⁻) decomposes to chlorate (ClO3⁻) and chlorine oxides. These results are incorporated into a simple box model to estimate the near-surface atmospheric methane lifetime. The model gives a lifetime on the order of hours to months depending on assumptions, substantially shorter than ~300 yrs. calculated from methane loss by gas-phase chemistry alone.
