Distribution and habitability of (meta)stable brines on present-day Mars
Edgard G. Rivera-Valentín, Vincent F. Chevrier, Alejandro Soto, Germán Martínez
发表信息：
Rivera-Valentin, E. G., Chevrier, V. F., Soto, A., Martinez, G. (2020) Distribution and habitability of (meta)stable brines on present-day Mars. Nat Astron 4, 756-761
Special Regions on Mars are defined as environments able to host liquid water that meets certain temperature and water activity requirements that allow known terrestrial organisms to replicate, and therefore could be habitable. Such regions would be a concern for planetary protection policies owing to the potential for forward contamination (biological contamination from Earth). Pure liquid water is unstable on the Martian surface, but brines may be present. Experimental work has shown that brines persist beyond their predicted stability region, leading to metastable liquids. Here we show that (meta)stable brines can form and persist from the equator to high latitudes on the surface of Mars for a few percent of the year for up to six consecutive hours, a broader range than previously thought. However, only the lowest eutectic solutions can form, leading to brines with temperatures of less than 225 K. Our results indicate that (meta)stable brines on the Martian surface and shallow subsurface (a few centimeters deep) are not habitable because their water activities and temperatures fall outside the known tolerances for terrestrial life. Furthermore, (meta)stable brines do not meet the Special Regions requirements, reducing the risk for forward contamination and easing threats related to the exploration of the Martian surface.
The Mars Science Laboratory (MSL) Rover Environmental Monitoring Station (REMS) has now made continuous in-situ meteorological measurements for several martian years at Gale crater, Mars. Of importance in the search for liquid formation are REMS' measurements of ground temperature and in-air measurements of temperature and relative humidity, which is with respect to ice. Such data can constrain the surface and subsurface stability of brines. Here we use updated calibrations to REMS data and consistent relative humidity comparisons (i.e., w.r.t. liquid vs w.r.t. ice) to investigate the potentia…
There may be a chance of small-scale ephemeral liquid water formation on present day Mars, even though the current climate does not support the existence of larger bodies of water. Through a process called deliquescence, hygroscopic salts can enter solution by absorbing water vapor directly from the atmosphere. Due to the absence of in-situ deliquescence experiments so far, the most reliable way to forecast deliquescence is through atmospherical modeling, however, the locations and times when salty liquid water could emerge are not yet well known. In this paper we present our results of likely…
During the Noachian, Mars' crust may have provided a favorable environment for microbial life. The porous brine-saturated regolith would have created a physical space sheltered from UV and cosmic radiations and provided a solvent, while the below-ground temperature and diffusion of a dense reduced atmosphere may have supported simple microbial organisms that consume H2 and CO2 as energy and carbon sources and produce methane as a waste. On Earth, hydrogenotrophic methanogenesis was among the earliest metabolisms but its viability on early Mars has never been quantitatively evaluated. Here we p…
Large alluvial fan deposits on Mars record relatively recent habitable surface conditions ($\lesssim$3.5 Ga, Late Hesperian - Amazonian). We find net sedimentation rate <(4-8) μm/yr in the alluvial-fan deposits, using the frequency of craters that are interbedded with alluvial-fan deposits as a fluvial-process chronometer. Considering only the observed interbedded craters sets a lower bound of >20 Myr on the total time interval spanned by alluvial-fan aggradation, >10^3-fold longer than previous lower limits. A more realistic approach that corrects for craters fully entombed in the fan deposit…
Martian subsurface habitability and astrobiology can be evaluated via a lava tube cave, without drilling. MACIE addresses two key goals of the Decadal Survey (2013-2022) and three MEPAG goals. New advances in robotic architectures, autonomous navigation, target sample selection, and analysis will enable MACIE to explore the Martian subsurface.
Observations of Water Frost on Mars with THEMIS: Application to the Presence of Brines and the Stability of (Sub)Surface Water Ice
Sorbonne Université, Centre National de la Recherche Scientifique (CNRS), École Polytechnique, École Normale Supérieure (ENS)（索邦大学，法国国家科学研究中心，巴黎综合理工学院，巴黎高等师范学院）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Northern Arizona University（北亚利桑那大学）；Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS/CNRS)（大气、介质、空间观测实验室）
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Microscopic liquid brines, especially calcium-perchlorate could emerge by deliquescence on Mars during night time hours. Using climate model computations and orbital humidity observations, the ideal periods and their annual plus daily characteristics at various past, current and future landing sites were compared. Such results provide context for future analysis and targeting the related observations by the next missions for Mars. Based on the analysis, at most (but not all) past missions' landing sites, microscopic brine could emerge during night time for different durations. Analysing the co…
Mars as an Exoplanet: Lessons from a Planet at the Edge of Habitability
University of California, Riverside（加州大学河滨分校）；Washington University, St. Louis（华盛顿大学圣路易斯分校）；Stanford University（斯坦福大学）；University of Colorado, Boulder（科罗拉多大学博尔德分校）
Study of exoplanets is one of the main goals of present research in planetary sciences and astrobiology. Analysis of huge planetary data from space missions such as CoRoT and Kepler is directed ultimately at finding a planet similar to Earth -- the Earth's twin, and answering the question of potential exo-habitability. The Earth Similarity Index (ESI) is a first step in this quest, ranging from 1 (Earth) to 0 (totally dissimilar to Earth). It was defined for the four physical parameters of a planet: radius, density, escape velocity and surface temperature. The ESI is further sub-divided into i…
Study of exoplanets has been of considerable interest for Astronomers, Planetary Scientists and Astrobiologists. Analysis of huge planetary data from space missions such as CoRoT and Kepler is directed ultimately at finding a planet similar to Earth- the Earth's twin, and looking for potential habitability. The Earth Similarity Index (ESI) is defined to find the similarity with Earth, which ranges from 1 (Earth) to 0 (totally dissimilar to Earth). ESI can be computed using four physical parameters of a planet, namely radius, density, escape velocity and surface temperature. The surface tempera…
Analyze Mass Spectrometry data with Artificial Intelligence to assist the understanding of past habitability of Mars and provide insights for future missions
Flowing water and brine have been proposed to cause seasonally reappearing dark streaks called recurring slope lineae (RSL) on steep warm slopes on Mars, along with other formation mechanisms that do not involve water. This study aims to examine whether the evaporation of water vapor from the RSL, whether from fresh water or brine, is detectable by observing water vapor and/or clouds. In this study, we summarize the possible rate and duration of water-vapor emission from RSL in different scenarios, simulate how the emitted water vapor behaves in a global climate model, and discuss the detectab…
There are four different stable climate states for pure water atmospheres, as might exist on so-called "waterworlds". I map these as a function of solar constant for planets ranging in size from Mars size to 10 Earth-mass. The states are: globally ice covered (Ts< 245K), cold and damp (270 < Ts< 290K), hot and moist (350< Ts< 550K) and very hot and dry (Ts< 900K). No stable climate exists for 290< Ts < 350K or 550 < Ts < 900K. The union of hot moist and cold damp climates describe the liquid water habitable zone, the width and location of which depends on planet mass. At each solar constant, t…
Mars exploration motivates the search for extraterrestrial life, the development of space technologies, and the design of human missions and habitations. Here we seek new insights and pose unresolved questions relating to the natural history of Mars, habitability, robotic and human exploration, planetary protection, and the impacts on human society. Key observations and findings include:(1)high escape rates of early Mars' atmosphere, including loss of water, impact present-day habitability;(2)putative fossils on Mars will likely be ambiguous biomarkers for life;(3)microbial contamination resul…
The low temperatures and high ultraviolet (UV) radiation levels at the surface of Mars today currently preclude the survival of life anywhere except perhaps in limited subsurface niches. Several ideas for making the martian surface more habitable have been put forward previously, but they all involve massive environmental modification that will be well beyond human capability for the foreseeable future. Here we present a new approach to this problem. We show that widespread regions of the surface of Mars could be made habitable to photosynthetic life in the future via a solid-state analogue to…
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Earth, Mars, and Venus, irradiated by an evolving Sun, have had fascinating but diverging histories of habitability. Although only Earth's surface is considered to be habitable today, all three planets might have simultaneously been habitable early in their histories. We consider how physical processes that have operated similarly or differently on these planets determined the creation and evolution of their atmospheres and surfaces over time. These include the geophysical and geochemical processes that determined the style of their interior dynamics and the presence or absence of a magnetic f…
In this Letter, we make use of sophisticated 3D numerical simulations to assess the extent of atmospheric ion and photochemical losses from Mars over time. We demonstrate that the atmospheric ion escape rates were significantly higher (by more than two orders of magnitude) in the past at $\sim 4$ Ga compared to the present-day value owing to the stronger solar wind and higher ultraviolet fluxes from the young Sun. We found that the photochemical loss of atomic hot oxygen dominates over the total ion loss at the current epoch whilst the atmospheric ion loss is likely much more important at anci…
The melt productivity of a differentiated planet's mantle is primarily controlled by its iron content, which is itself approximated by the planet's core mass fraction (CMF). Here we show that estimates of an exo-planet's CMF allows robust predictions of the thickness, composition and mineralogy of the derivative crust. These predicted crustal compositions allow constraints to be placed on volatile cycling between surface and the deep planetary interior, with implications for the evolution of habitable planetary surfaces. Planets with large, terrestrial-like, CMFs ($\geq$0.32) will exhibit thin…
We investigate the prospects for the past or current existence of habitable conditions deep underneath the surfaces of the Moon and Mars as well as generic bound and free-floating extrasolar rocky objects. We construct a simple model that takes into account the thermal limits of life as well as the size, surface temperature, and relative radionuclide abundance of a given object and yields the spatial extent of the subsurface habitable region. We also investigate the constraint imposed by pressure on habitability, and show that it is unlikely to rule out the prospects for life altogether. We es…
M type stars are good targets in the search for habitable extrasolar planets. Because of their low effective temperatures, the habitable zone of M stars is very close to the star itself. For planets close to their stars, tidal heating plays an important role in thermal and orbital evolutions, especially when the planet orbit has a relatively large eccentricity. Although tidal heating interacts with the thermal state and orbit of the planet, such coupled calculations for extrasolar planets around M star have not been conducted. We perform coupled calculations using simple structural and orbital…
Current water trapping micro-habitats on the surface of Mars
ELTE Eötvös Loránd University（厄特沃什·罗兰大学）；HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Observatory（匈牙利科学院天文学与地球科学研究中心，孔科利天文台）；European Astrobiology Institute（欧洲天体生物学研究所）
We investigate the global seasonal variations of near-surface relative humidity and relevant attributes, like temperature and water vapor volume mixing ratio on Mars using calculations from modelled and measurement data. We focus on 2 am local time snapshots to eliminate daily effects related to differences in insolation, and to be able to compare calculations based on modelling data from the LMDZ GCM with the observations of MGS TES. We study the seasonal effects by examining four specific dates in the Martian year, the northern spring equinox, summer solstice, autumn equinox and winter solst…
Present-day Mars is cold and dry, but mineralogical and morphological evidence shows that liquid-water existed on the surface of ancient Mars. In order to explain this evidence and assess ancient Mars's habitability, one must understand the size and composition of the ancient atmosphere. Here we place constraints on the ancient Martian atmosphere by modeling the coupled, self-consistent evolution of atmospheric CO2, N2, and Ar on Mars from 3.8 billion years ago (Ga) to the present. Our model traces the evolution of these species' abundances and isotopic composition caused by atmospheric escape…
There is growing evidence suggesting the presence of aqueous environment on ancient Mars, raising the question of the possibility of life in such an environment. Subsequently, with the erosion of the Martian atmosphere resulting in drastic changes in its climate, surface water disappeared, shrinking habitable spaces on the planet, with only a limited amount of water remaining near the surface in form of brines and water-ice deposits. Life, if it ever existed, would have had to adapt to harsh modern conditions, which includes low temperatures and surface pressure, and high radiation dose. Prese…
Precipitation and its response to forcings is an important aspect of planetary climate system. In this study, we examine the strength of precipitation in the experiments with different atmospheric masses and their response to surface warming, using three global atmospheric general circulation models (GCMs) and one regional cloud-resolving model (CRM). We find that precipitation is weaker when atmospheric mass is larger for a given surface temperature. Furthermore, the increasing rate of precipitation with increasing surface temperature under a larger atmospheric mass is smaller than that under…
How habitable are M-dwarf Exoplanets? Modeling surface conditions and exploring the role of melanins in the survival of Aspergillus niger spores under exoplanet-like radiation
Whereas the Solar System has Mars and Europa as the best candidates for finding fossil/extant life as we know it - based on complex carbon compounds and liquid water - the 263 (non-pulsar) planetary systems around other stars as known at 15 September 2008 could between them possess many more planets where life might exist. Moreover, the number of these exoplanetary systems is growing steadily, and with this growth there is an increase in the number of planets that could bear carbon-liquid water life. In this brief review the main methods by which exoplanets are being discovered are outlined, a…
The Goldilocks problem for detecting water in terrestrial planets: Constraining water abundances in the mid-IR with LIFE
University of Edinburgh（爱丁堡大学）；York University（约克大学）；ETH Zurich（苏黎世联邦理工学院）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；German Aerospace Center (DLR)（德国航空航天中心（DLR））；Free University of Berlin（柏林自由大学）；University of Groningen（格罗宁根大学）；University of Bern（伯尔尼大学）
