Early Martian Environment Research Articles

The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

AbstractAlthough there is little doubt that rivers once flowed on Mars' surface, how sustained and frequent their flows were remains enigmatic. Understanding the hydrology of early Mars, nonetheless, is a prerequisite to resolving the planet's climate history and the astrobiological potential of various ancient putative ecosystems. In 2021, NASA's Perseverance rover will attempt to land near ancient fluviodeltaic deposits in Jezero crater. Deltas offer enhanced organic‐matter burial and preservation on Earth but translating this notion to early Martian environments remains speculative in the absence of information on flow intermittency and sedimentation rates. Here we develop a new model to infer the lateral migration rate of Martian river meanders, which, combined with orbiter‐based observations of the fluviodeltaic deposits at Jezero crater, allows us to determine a minimum timescale for the formation of its delta. We then independently constrain the total duration of delta formation, including dry spells. Our best estimates suggest that delta formation spanned ~19–37 years over a total duration of ~380,000 years, i.e., that rivers flowed for a minimum ~1 sol/15–30 Martian years and conceivably more frequently, but uncertainties on total duration are large. Despite a possibly arid climate, predicted sedimentation rates are high, suggesting a rapid burial of putative organics in distal deposits. Altogether, our results support Jezero crater's potential as a prime target to look for ancient Martian life and acquire samples to return to Earth. Any discrepancies between our predictions of the deposits' grain‐to‐bedform‐scale architecture and future rover observations will shed critical light onto Mars' early surface environments.

Grain Size Variations in the Murray Formation: Stratigraphic Evidence for Changing Depositional Environments in Gale Crater, Mars

AbstractThe lowermost exposure of the Murray formation in Gale crater, Mars, was interpreted as sediment deposited in an ancient lake based on data collected by the Curiosity rover. Constraining the stratigraphic extent and duration of this environment has important implications for the paleohydrology of Gale. Insights into early Martian environments and paleofluid flow velocity can be obtained from grain size in rocks. Visual inspection of grain size is not always available for rocks investigated at field sites on Mars due to limited image coverage. But grain sizes can also be estimated from the Gini Index Mean Score, a grain‐size proxy that uses point‐to‐point chemical variations in ChemCam Laser Induced Breakdown Spectroscopy data. New Gini Index Mean Score results indicate that the Murray formation is dominated by mudstones with grains smaller than the spatial resolution of all rover cameras. Intervals of fine to coarse sandstone also are present, some of which are verified using observations of grain size and sedimentary structures in associated images. Overall, results demonstrate that most of the Murray consists of mudstone, suggesting settling of grains from suspension in low energy depositional environments such as lakes. Some of the mudstones contain desiccation cracks indicating periods of drying with a lowering of lake water level. However, beds and lenses of cross‐bedded sandstones are common at specific intervals, suggesting episodes of fluvial and possibly eolian deposition. The persistence of lacustrine deposits interspersed with fluvial deposits suggests that liquid water was sustained on the Martian surface for tens of thousands to millions of years.

A coupled atmosphere–hydrosphere global climate model of early Mars: A ‘cool and wet’ scenario for the formation of water channels

Martian water channels are considered evidence of a climate warm enough to allow the existence of long-term fluvial systems on early Mars during the Noachian and Hesperian boundary (3.85–3.6 Ga). Quantitative inferences of water channel formation from climate models are crucial to develop an accurate understanding of the early Martian environment. We present the results of a newly developed 3-dimensional Paleo Martian Global Climate Model (PMGCM) assuming a CO2/H2O/H2 atmosphere under the ‘Faint Young Sun’ condition (with a solar luminosity of ~75% of the current value) for surface pressures between 0.5 and 2 bar. The PMGCM has a hydrologic cycle module, which includes ocean thermodynamics and water vapor advection, convection, condensation and precipitation processes, as well as calculations of surface fluvial activities (e.g., fluvial activity and sediment transport) at a high horizontal resolution.Our PMGCM results show that the early Martian surface environment could have been ‘cool’ (between ‘warm’ and ‘cold’); namely, the surface temperatures could have been high enough (>273 K) during summertime to allow seasonal melting of snow and ice deposits, and low enough (<273 K) during wintertime to produce considerable snow precipitation and accumulation, under the conditions of a mean surface pressure of approximately 1.5 bar and an H2 composition of 3%. The results also indicate that a ‘wet’ surface environment should be characterized by precipitation and seasonal melting of snow and ice (neither ‘dry’ nor ‘permanently frozen’ states), and enough fluvial activity and sediment transport could have occurred in the low to middle latitudes to produce Martian valley networks within a relatively short time (less than tens of million years). Therefore, we suggest that a moderate climate, that is, ‘cool and wet’ conditions lying between ‘warm and wet’ and ‘cold and frozen’, best explains the fluvial activity on early Mars.

Nitrate-Dependent Iron Oxidation: A Potential Mars Metabolism.

This work considers the hypothetical viability of microbial nitrate-dependent Fe2+ oxidation (NDFO) for supporting simple life in the context of the early Mars environment. This draws on knowledge built up over several decades of remote and in situ observation, as well as recent discoveries that have shaped current understanding of early Mars. Our current understanding is that certain early martian environments fulfill several of the key requirements for microbes with NDFO metabolism. First, abundant Fe2+ has been identified on Mars and provides evidence of an accessible electron donor; evidence of anoxia suggests that abiotic Fe2+ oxidation by molecular oxygen would not have interfered and competed with microbial iron metabolism in these environments. Second, nitrate, which can be used by some iron oxidizing microorganisms as an electron acceptor, has also been confirmed in modern aeolian and ancient sediment deposits on Mars. In addition to redox substrates, reservoirs of both organic and inorganic carbon are available for biosynthesis, and geochemical evidence suggests that lacustrine systems during the hydrologically active Noachian period (4.1–3.7 Ga) match the circumneutral pH requirements of nitrate-dependent iron-oxidizing microorganisms. As well as potentially acting as a primary producer in early martian lakes and fluvial systems, the light-independent nature of NDFO suggests that such microbes could have persisted in sub-surface aquifers long after the desiccation of the surface, provided that adequate carbon and nitrates sources were prevalent. Traces of NDFO microorganisms may be preserved in the rock record by biomineralization and cellular encrustation in zones of high Fe2+ concentrations. These processes could produce morphological biosignatures, preserve distinctive Fe-isotope variation patterns, and enhance preservation of biological organic compounds. Such biosignatures could be detectable by future missions to Mars with appropriate instrumentation.

The western Qaidam Basin as a potential Martian environmental analogue: An overview

AbstractThe early Martian environment is interpreted as warmer and wetter, before a significant change in its global climatic conditions irreversibly led to the current hyperarid environments. This transition is one of the most intriguing processes of Martian history. The extreme climatic change is preserved in the salt deposits, desiccated landscapes, and geomorphological structures that were shaped by the evaporation of water. However, until a manned journey to Mars is feasible, many Martian materials, morphological structures, and much of its evolutionary history will continue to be poorly understood. In this regard, searching and investigating Martian analogues are still meaningful. To find an Earth environment with a whole set of Martian structures distributed at a scale comparable to Mars is even more important to test landing crafts and provide optimized working parameters for rovers. The western Qaidam Basin in North Tibetan Plateau is such a Martian analogue. The area harbors one of the most extreme hyperarid environments on Earth and contains a series of ancient lakes that evaporated at different evolutionary stages during the rise of the Tibetan Plateau. Large quantities of salts and geomorphological features formed during the transition of warmer‐and‐wet to colder‐and‐dry conditions provide unique references to study the modern Martian surface and interpret the orbital data. We present numerous similarities and results of investigations that suggest the Qaidam Basin as a potential analogue to study modern geomorphic processes on Mars, and suggest that this is an essential site to test future Mars sample return missions.

Introduction to the Early Mars III Special Section and Key Questions from the Third International Conference on Early Mars

The influx of new data received from recent spacecraft missions, the study of Martian meteorites, recent progress in early climate modeling, the growing evidence for abundant water on early Mars, and the rapid pace of new discoveries about the origin and diversity of life on Earth have reinvigorated interest in both the conditions that prevailed on Mars during its first ~1.5 billion years of geologic history and their potential implications for the development of life. These issues were initially discussed at the First Early Mars Conference, which was held in Houston, Texas, in April 1997 and then again at the Second Early Mars Conference, which was held in Jackson Hole, Wyoming, in October 2004. The scientific content of these meetings was captured in the meeting abstracts, Key Questions (identified by the meeting participants and reported to the Mars Exploration Program Analysis Group, MEPAG), and two associated Special Sections of JGR-Planets, which were published in December 1998 (with 12 papers) and December 2005 (with 25 papers). On 21–25 May 2012, about 100 scientists gathered at the Hyatt Regency Hotel in Lake Tahoe, Nevada to participate in the Third International Conference on Early Mars: Geologic and Hydrologic Evolution, Physical and Chemical Environments, and the Implications for Life. Like its predecessors, the Third Early Mars Conference brought together scientists from fields as diverse as planetary geology, atmospheres, climate, meteoritics, microbiology, and molecular biochemistry, to discuss the conditions that prevailed on the early Earth and Mars during their first ~1.5 billion years of geologic history. Indeed, the study of early Mars is likely to provide critical insight into understanding the nature of the early Earth—for as much as 40% of the Martian surface is believed to date back to a period from which little survives in the Earth's geologic record [Tanaka, 1986]. To ensure enough time to rigorously assess our current understanding of early Martian environments, promote the exchange of new ideas, and address some of the most critical and controversial issues in Mars research, approximately 50% of the total program (which consisted of a mix of invited and contributed talks, panel discussions, poster presentations, several special sessions, a conference dinner, and a mid-conference field trip to Mono Lake) was reserved for discussion and debate. Some of the specific issues and questions that were addressed at the meeting included those identified as Key Questions at the Second Conference on Early Mars, which was held in 2004 [Beaty et al., 2005]. The Third Conference ended with an extended discussion, led by Mike Carr and David Des Marais, to update these “Key Questions” (Table 1), which will serve as the Conference input into the next revision of the MEPAG Science Goals and Objectives document. As with the previous Early Mars Conferences, this special section of JGR-Planets was organized to highlight some of the scientific issues discussed at the meeting. The topics covered include discussions of core-mantle differentiation [Rai and van Westrenen, 2013], the history of the Martian dynamo [Lillis et al., 2013], the preservation state of Noachian terrains [Irwin et al., 2013], the relationship between the morphometry of valley networks [Ansan and Mangold, 2013], crater lake deltas [Hauber et al., 2013; de Villiers et al., 2013], and atmospheric dust [Kahre et al., 2013] in the evolution of the planet's climate; the role of serpentinization in the depletion of the planet's inventory of water [Chassefière et al., 2013]; the origin of the interior deposits of Gale crater [Le Deit et al., 2013]; acid-sulfate alteration of basalt in early hydrothermal systems [Hynek et al., 2013; McCollom et al., 2013]; the impact formation of hydrated silicates [Tornabene et al., 2013]; and the role of impact basin tectonics on Noachian flood volcanism [Rogers and Nazarian, 2013]. The conveners would like to thank the following organizations for their substantial contributions to the success of the meeting: the Lunar and Planetary Institute (for organizational, logistical and financial support), NASA's Mars Program Office (for student travel support), and especially to the NASA's Mars Data Analysis Program which provided the initial funding that made the organization of this meeting possible. Part of this work was carried out at the Jet Propulsion Laboratory/California Institute of Technology, under a contract from National Aeronautics and Space Administration. This is LPI Contribution #1790. The program and abstracts for the Third Early Mars Conference can be found at: http://www.lpi.usra.edu/meetings/earlymars2012/pdf/program.pdf

Contrasting styles of water–rock interaction at the Mars Exploration Rover landing sites

The nature of ancient hydrological systems on Mars has been the subject of ongoing controversy, driven largely by a disconnect between observational evidence for flowing water on the Martian surface at multiple scales and the incompatibility of such observations with theoretical models that predict a cold early Martian environment in which liquid water is unstable. Here we present geochemical data from the Mars Exploration Rovers to evaluate the hydrological conditions under which weathering rinds, soils, and sedimentary rocks were formed. Our analysis indicates that the chemistry of rinds and soils document a water-limited hydrologic environment where small quantities of S-bearing fluids enter the system, interact with and chemically alter rock and soil, and precipitate secondary mineral phases at the site of alteration with little to no physical separation of primary and secondary mineral phases. In contrast, results show that the sedimentary rocks of the Burns Formation at Meridiani Planum have a chemical composition well-described as a mixture between siliciclastic sediment and sulfate-bearing salts derived from the evaporation of groundwater. We hypothesize that the former may be derived from the recently investigated Shoemaker Formation, a sequence of impact breccias that underlie the Burns Formation. This result has important implications for the style of chemical weathering and hydrology recorded by these sedimentary materials, revealing long-range transport of ions in solution in an open hydrological system that is consistent only with subsurface or overland flow of liquid water.

Readily available phosphate from minerals in early aqueous environments on Mars

Phosphate is thought to be a chemical nutrient essential for life, but the low solubility of phosphate minerals means that abiogenesis on Earth had to overcome the hurdle of phosphate-limited environments. Dissolution experiments of phosphate minerals commonly found on Mars suggest that phosphate may have been more readily available in early martian environments.

Impact‐induced hydrothermal activity on early Mars

We report on numerical modeling results of postimpact cooling of craters with diameters of 30, 100, and 180 km in an early Martian environment, with and without the presence of water. The effects of several variables, such as ground permeability and the presence of a crater lake, were tested. Host rock permeability is the main factor affecting fluid circulation and lifetimes of hydrothermal systems, and several permeability cases were examined for each crater. The absence of a crater lake decreases the amount of circulating water and increases the system lifetime; however, it does not dramatically change the character of the system as long as the ground remains saturated. It was noted that vertical heat transport by water increases the temperature of localized near‐surface regions and can prolong system lifetime, which is defined by maximum near‐surface temperature. However, for very high permeabilities this effect is negated by the overall rapid cooling of the system. System lifetimes, which are defined by near‐surface temperatures and averaged for all permeability cases examined, were 67,000 years for the 30‐km crater, 290,000 years for the 100‐km crater, and 380,000 for the 180‐km crater. Also, an approximation of the thermal evolution of a Hellas‐sized basin suggests potential for hydrothermal activity for ∼10 Myr after the impact. These lifetimes provide ample time for colonization of impact‐induced hydrothermal systems by thermophilic organisms, provided they existed on early Mars. The habitable volume reaches a maximum of 6,000 km38,500 years after the impact in the 180‐km crater model.

Fluvial sedimentary deposits on Mars: Ancient deltas in a crater lake in the Nili Fossae region

New spacecraft observations in the Nili Fossae region of Mars reveal two valley networks (∼80 and ∼200 km long) that each formed distributary fans as they entered an ancient 40‐km diameter impact crater. An outlet channel on the eastern crater rim, lying at an elevation above the fans, suggests these fans formed as subaqueous deltas in a crater lake. Water flowing in the valley networks entered the crater and deposited the fans, and ponded to a maximum depth of about 450 m. The lake then overtopped and breached the crater rim, incising it and dropping the lake level by ∼100 m. Geological evidence, combined with the volume of water necessary to fill the crater, suggests the duration of flow through this system was prolonged. The existence of the deposits described here implies that the early Martian environment supported overland flow and ponding of water for an extended period of time.

Crater morphometry and modification in the Sinus Sabaeus and Margaritifer Sinus regions of Mars

Degraded craters in the southern highlands are indicative of an early martian climate much different than the present. Using a photoclinometric model, analyses of degraded crater morphometry have revealed the stages of crater modification and, for the first time, allow a quantitative assessment of the amount of material eroded in the highlands. Central peaks of fresh craters are removed early by degradational processes. The sharp rims of fresh craters also become rounded while the interior slopes become shallower. Continued degradation causes the crater rim to lower, and infilling produces a broad, flat crater floor. Contrary to earlier observations, the degree of rim modification does not appear to be dependent on the presence of ancient valley networks. During degradation, the diameter of the impact craters also increases due to backwasting. A simple algebraic model balancing the measured amount of infilling with that eroded from the interior slopes suggests that the crater diameters were enlarged by 7 to 10% initially, agreeing with prior observations. These models suggest that larger diameter (i.e., 50 km) craters were enlarged a greater amount than smaller diameter craters, which is opposite to what should be observed. To explain this discrepancy, a ∼10 m thick deposit, presumably aeolian in origin, must have been emplaced within the crater interiors following cessation of the degradational process. By the terminal stage of degradation, crater diameters appear to have been enlarged by 30%. In addition, a deposit ∼60 m average thickness must have been emplaced within these rimless craters to explain the discrepancy in crater enlargement. Because this deposit is contained only within the highly eroded, rimless craters, this material most likely originated from erosion of the surrounding terrain. The measured crater morphometry has allowed us to develop equations describing the amount of material eroded at any given stage of degradation. Applying these equations to craters within the Margaritifer Sinus and Sinus Sabaeus region indicates that an equivalent of ∼200 m of highland material was eroded and redistributed within the study area. Depending upon model chronology, degradation operated for either 400 or 600 million years, suggesting that erosion rates were on the order of ∼0.0003 to 0.0005 mm/yr. These erosion rates are equivalent to those determined for terrestrial periglacial environments. Two‐dimensional simulations of some possible degradational processes suggest that fluvial erosion and deposition combined with diffusional creep come closest to producing equivalent degrees of modification through the range of crater diameters investigated in this study (20 to 50 km). However, these processes are inefficient at producing the amount of crater enlargement observed, suggesting that crater interior slopes may have also been undermined by sapping. These results imply that geologic processes related to precipitation dominated the early martian environment. Our working hypothesis is that this precipitation was due to the presence of a primordial atmosphere which condensed and collapsed (i.e., precipitated) into the martian regolith; a process which ceased during the late Hesperian/early Amazonian (3.5 to 1.8 Ga).

火星の生命 ＰＡＲＴ２ 火星の環境と生命

Five conditions for life to arise are discussed with referring to early Martian environment. The key to determine whether any life form appeared on Mars is found to be the early Martian carbon dioxide atmospheric pressure and then the temperature. The importance to determine the heat flow is indicated. The items to be measured for future Martian exploration are listed. The surface materials, which has been poorly understood, are emphasized for further exploration. Two strategies for search for life on Mars, "step by step" strategy and quick strategy, are suggested.

The use of mineral crystals as bio-markers in the search for life on Mars

Photographs that depict presumed fluvial features on the martian surface have led geologists to hypothesize that water flowed across the early martian terrain. From this, it has been further hypothesized that the surface and atmospheric conditions on early Mars were similar to those on early Earth. Because the oldest fossil evidence of life on Earth dates back to this early period, at least 3.5 billion years ago /1/, the possibility exists that the early Martian environment could have also been conducive to the origin of life. To investigate this possibility, universal signatures or bio-markers indicative of past (or present) biological activity must be identified for use in the search for life on Mars. Several potentially applicable biomarkers have been identified and include: organics (e.g., specific classes of lipids and hopanes), suites of specific inorganic and organic compounds, as well as the isotopic ratios of C, N, and S /2/. Unfortunately, all of these biomarkers may be biologic or abiotic origin; these origins are often difficult to distinguish. Thus, the discovery of any one of these compounds alone is not a bio-marker. Because minerals produced under biologic control have distinctive crystallographies, morphologies, and isotopic ratios that are distinguishable from abiotically produced minerals with the same chemical composition, and are stable through geologic time, we propose the use of minerals resulting from biologically controlled mineralization processes as bio-markers.

Early martian environments: The Antarctic and other terrestrial analogs

The comparability of the early environments of Mars and Earth, and the biological evolution which occurred on early earth, motivates serious consideration of the possibility of an early martian biota. Environments which could have contained this early martian life and which may presently contain evidence of this former life include aquatic, ice, soil, and rock habitats. Several analogs of these potential early martian environments, which can provide useful information in searching for extinct life on Mars, are currently available for study on Earth. These terrestrial analogs include the perennially ice-covered lakes and sandstone rocks in the Polar Deserts of Antarctica, surface of snowfields and glaciers, desert soils, geothermal springs, and deep subsurface environments.

Age of Craters on Mars

The rate of crater formation on Mars is calculated to be about 25 times higher than that on the Moon. The crater density observed by Mariner IV points to an age only one-sixth that of the lunar maria, or 300 to 800 million years. Hence no conclusions can presently be drawn from these photographs concerning the early Martian environment.