Early Martian Surface Research Articles

Sustained wet-dry cycling on early Mars.

The presence of perennially wet surface environments on early Mars is well documented1,2, but little is known about short-term episodicity in the early hydroclimate3. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet theseare rarely preserved in the sedimentary record4. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results5,6. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet-dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet-dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes5, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet-dry cycling can promote prebiotic polymerization7,8, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition1. This indicates that the Noachian-Hesperian transition (3.8-3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

Unravelling surface and subsurface carbon sinks within the early Martian crust

Understanding the climate history of Mars, one of our closest planetary neighbours, has important implications for understanding the environmental evolution of Earth and other rocky planets in general. The widespread recognition of an extensive sedimentary record modified, at least in part, by liquid water holds much promise to provide evidence about Mars' past. However, unravelling the pressure and compositional history of Mars' Noachian atmosphere has remained problematic. Based on expected outgassing behaviour, observed atmospheric isotope ratios, and climate models, carbon dioxide is widely considered a main constituent of the early Martian atmosphere. If this was indeed the case, it is surprising that carbonate minerals, the expected sinks for this carbon, are only abundant in a few isolated localities across the Martian surface. Three broad possibilities may account for this apparent inconsistency: (1) carbonates formed under pCO2 higher than present but were buried, or subsequently destroyed; (2) Noachian atmospheric pCO2 was significantly lower than current estimates; or (3) low-temperature carbonate formation was kinetically controlled under the aqueous conditions that characterised much of the early Martian surface. While orbital spectroscopic investigations have yielded an increasing inventory of isolated carbonate-bearing deposits, their relative rarity at the near-surface has prompted suggestions that the Noachian atmosphere was commonly characterised by low pCO2. Without a more complete investigation of the carbonate-forming processes occurring within the ancient crust, no hypothesis can be tested robustly. Here, we examine the controls on Fe(II)-carbonate precipitation in low-temperature, anoxic water-rock systems as a function of pCO2. In experiments lasting up to 85 days, no measurable Fe(II)-carbonate precipitation occurred within the limits of analytical detection, despite significant and sustained supersaturation with respect to siderite. These observations are quantitatively consistent with recent investigations highlighting a significant supersaturation threshold for Fe(II)-carbonate nucleation. Reaction path models that incorporate these constraints indicate that Fe(II)-carbonate supersaturation thresholds would have been commonly met in low water:rock ratio systems isolated from the Noachian atmosphere as opposed to high water:rock ratio, open-systems exposed at the near surface. These results suggest the rarity of carbonates exposed at or near the surface of Mars may be controlled, at least in part, by a lack of deep crustal exposures and lack of the geochemical conditions conducive to carbonate formation, rather than insufficient atmospheric pCO2. Such geochemical constraints are in turn consistent with available orbital data indicating that carbonates may be more abundant within the deep crust, potentially representing a significant subsurface carbon sink.

Groundwater Release on Early Mars: Utilizing Models and Proposed Evidence for Groundwater Release to Estimate the Required Climate and Subsurface Water Budget

AbstractIt has been proposed that groundwater was released onto the early martian surface in several locations, including Meridiani Planum, NE Hellas, Terra Sirenum, the northern lowlands, and Gale crater. We assume that groundwater was released in a manner similar to a groundwater‐fed lake on Earth and then use a combination of a global climate model and mathematical relationships to place lower limit estimates on the early climate and subsurface water inventory that are required for groundwater release to occur at all of these locations. We find that the minimum required conditions are global mean annual temperature >284 K and a subsurface water inventory >496 m global equivalent layer. Additionally, thermal models predict that if such warm conditions occurred from punctuated heating in an otherwise “cold and icy” climate, the warm conditions must have persisted for thousands of years in order to remove the cryosphere and permit groundwater release.

Warming early Mars with climate cycling: The effect of [formula omitted]-[formula omitted] collision-induced absorption

Explaining the evidence for surface liquid water on early Mars has been a challenge for climate modelers, as the sun was ∼30% less luminous during the late-Noachian. We propose that the additional greenhouse forcing of CO2-H2 collision-induced absorption is capable of bringing the surface temperature above freezing and can put early Mars into a limit-cycling regime. Limit cycles occur when insolation is low and CO2 outgassing rates are unable to balance with the rapid drawdown of CO2 during warm weathering periods. Planets in this regime will alternate between global glaciation and transient warm climate phases. This mechanism is capable of explaining the geomorphological evidence for transient warm periods in the martian record. Previous work has shown that collision-induced absorption of CO2-H2 was capable of deglaciating early Mars, but only with high H2 outgassing rates (greater than ∼600 Tmol/yr) and at high surface pressures (between 3 to 4 bars). We used new theoretically derived collision-induced absorption coefficients for CO2-H2 to reevaluate the climate limit cycling hypothesis for early Mars. Using the new and stronger absorption coefficients in our 1-dimensional radiative convective model as well as our energy balance model, we find that limit cycling can occur with an H2 outgassing rate as low as ∼300 Tmol/yr at surface pressures below 3 bars. Our results agree more closely with paleoparameters for early martian surface pressure and hydrogen abundance.

Magnetite Authigenesis and the Warming of Early Mars.

The Curiosity rover has documented lacustrine sediments at Gale Crater, but how liquid water became physically stable on the early Martian surface is a matter of significant debate. To constrain the composition of the early Martian atmosphere during sediment deposition, we experimentally investigated the nucleation and growth kinetics of authigenic Fe-minerals in Gale Crater mudstones. Experiments show that pH variations within anoxic basaltic waters trigger a series of mineral transformations that rapidly generate magnetite and H2(aq). Magnetite continues to form through this mechanism despite high PCO2 and supersaturation with respect to Fe-carbonate minerals. Reactive transport simulations that incorporate these experimental data show that groundwater infiltration into a lake equilibrated with a CO2-rich atmosphere can trigger the production of both magnetite and H2(aq) in the mudstones. H2(aq), generated at concentrations that would readily exsolve from solution, is capable of increasing annual mean surface temperatures above freezing in CO2-dominated atmospheres. We therefore suggest that magnetite authigenesis could have provided a short-term feedback for stabilizing liquid water, as well as a principal feedstock for biologically relevant chemical reactions, at the early Martian surface.

Climate of early Martian surface and loss of water – A review

Mars is one of the interesting planets for geoscientists to explore the presence of water on the surface of terrestrial planets. The age, geology and geomorphic processes of Mars are almost similar to Earth surface processes. However, earth has tremendous influence of tectonism. The Martian surface once it was flourishing with water flow and formations of fluvial channels, lakes, deltas and oceans. The planet Mars evolved through ages with different climatic conditions from warm wetter period to cold drier period. In the present paper, different climatic condition and the reasons for escape of water from surface of Mars are discussed.

Atmospheric Constraints on the Surface UV Environment of Mars at 3.9 Ga Relevant to Prebiotic Chemistry.

Recent findings suggest that Mars may have been a clement environment for the emergence of life and may even have compared favorably to Earth in this regard. These findings have revived interest in the hypothesis that prebiotically important molecules or even nascent life may have formed on Mars and been transferred to Earth. UV light plays a key role in prebiotic chemistry. Characterizing the early martian surface UV environment is key to understanding how Mars compares to Earth as a venue for prebiotic chemistry. Here, we present two-stream, multilayer calculations of the UV surface radiance on Mars at 3.9 Ga to constrain the surface UV environment as a function of atmospheric state. We explore a wide range of atmospheric pressures, temperatures, and compositions that correspond to the diversity of martian atmospheric states consistent with available constraints. We include the effects of clouds and dust. We calculate dose rates to quantify the effect of different atmospheric states on UV-sensitive prebiotic chemistry. We find that, for normative clear-sky CO2-H2O atmospheres, the UV environment on young Mars is comparable to young Earth. This similarity is robust to moderate cloud cover; thick clouds (τcloud ≥ 100) are required to significantly affect the martian UV environment, because cloud absorption is degenerate with atmospheric CO2. On the other hand, absorption from SO2, H2S, and dust is nondegenerate with CO2, meaning that, if these constituents build up to significant levels, surface UV fluence can be suppressed. These absorbers have spectrally variable absorption, meaning that their presence affects prebiotic pathways in different ways. In particular, high SO2 environments may admit UV fluence that favors pathways conducive to abiogenesis over pathways unfavorable to it. However, better measurements of the spectral quantum yields of these pathways are required to evaluate this hypothesis definitively. Key Words: Radiative transfer-Origin of life-Mars-UV radiation-Prebiotic chemistry. Astrobiology 17, 687-708.

Impact induced surface heating by planetesimals on early Mars

We investigate the influence of impacts of large planetesimals and small planetary embryos on the early Martian surface on the hydrodynamic escape of an early steam atmosphere that is exposed to the high soft X-ray and EUV flux of the young Sun. Impact statistics in terms of number, masses, velocities, and angles of asteroid impacts onto the early Mars are determined via n-body integrations. Based on these statistics, smoothed particle hydrodynamics (SPH) simulations result in estimates of energy transfer into the planetary surface material and according surface heating. For the estimation of the atmospheric escape rates we applied a soft X-ray and EUV absorption model and a 1-D upper atmosphere hydrodynamic model to a magma ocean-related catastrophically outgassed steam atmosphere with surface pressure values of 52 bar H2O and 11 bar CO2. The estimated impact rates and energy deposition onto an early Martian surface can account for substantial heating. The energy influx and conversion rate into internal energy is most likely sufficient to keep a shallow magma ocean liquid for an extended period of time. Higher surface temperatures keep the outgassed steam atmosphere longer in vapor form and therefore enhance its escape to space within about 0.6 Myr after its formation.

An impact-induced, stable, runaway climate on Mars

Large asteroid and comet impacts on Mars, such as the one that formed the Argyre basin, delivered considerable amounts of kinetic energy to the planet and raised the surface temperature hundreds of degrees. The impact that formed the Argyre basin occurred 3.8–3.9byr ago (Werner, S.C. [2008]. Icarus 195, 45–60; Fassett, C.I., Head, J.W. [2011]. Icarus 211, 1204–1214), during the time of formation of fluvial features on the early martian surface, and was capable of causing global-scale precipitation and warming of the surface. Dual solutions to the climate of early Mars, one cold like present Mars and the other in a hot runaway state, exist for the pressure range of 0.006–1bar of CO2, and for water inventories 6.5bars or greater. A large impact event may have pushed Mars to a long-lasting hot runaway state. The runaway state would persist until escape processes reduced water vapor and forced the planet to return to a cold climate.

Decreasing CO2partial pressure triggered Mg-Fe-Ca carbonate formation in ancient Martian crust preserved in the ALH84001 Meteorite

We retrace hydrogeochemical processes leading to the formation of Mg–Fe–Ca carbonate concretions (first distinct carbonate population, FDCP) in Martian meteorite ALH84001 by generic hydrogeochemical equilibrium and mass transfer modeling. Our simple conceptual models assume isochemical equilibration of orthopyroxenite minerals with pure water at varying water-to-rock ratios, temperatures and CO2 partial pressures. Modeled scenarios include CO2 partial pressures ranging from 10.1325 to 0.0001 MPa at water-to-rock ratios between 4380 and 43.8 mol mol−1 and different temperatures (278, 303 and 348 K) and enable the precipitation of Mg–Fe–Ca solid solution carbonate. Modeled range and trend of carbonate compositional variation from magnesio-siderite (core) to magnesite (rim), and the precipitation of amorphous SiO2 and magnetite coupled to magnesite-rich carbonate are similar to measured compositional variation. The results of this study suggest that the early Martian subsurface had been exposed to a dynamic gas pressure regime with decreasing CO2 partial pressure at low temperatures (approximately 1.0133 to 0.0001 MPa at 278 K or 6 to 0.0001 MPa at 303 K). Moderate water-to-rock ratios of ca. 438 mol mol−1 and isochemical weathering of orthopyroxenite are additional key prerequisites for the formation of secondary phase assemblages similar to ALH84001’s ‘FDCP’. Outbursts of water and CO2(g) from confined ground water in fractured orthopyroxenite rocks below an unstable CO2 hydrate-containing cryosphere provide adequate environments on the early Martian surface.

Solar UV Irradiation Conditions on the Surface of Mars¶

The UV radiation environment on planetary surfaces and within atmospheres is of importance in a wide range of scientific disciplines. Solar UV radiation is a driving force of chemical and organic evolution and serves also as a constraint in biological evolution. In this work we modeled the transmission of present and early solar UV radiation from 200 to 400 nm through the present-day and early (3.5 Gyr ago) Martian atmosphere for a variety of possible cases, including dust loading, observed and modeled O3 concentrations. The UV stress on microorganisms and/or molecules essential for life was estimated by using DNA damaging effects (specifically bacteriophage T7 killing and uracil dimerization) for various irradiation conditions on the present and ancient Martian surface. Our study suggests that the UV irradiance on the early Martian surface 3.5 Gyr ago may have been comparable with that of present-day Earth, and though the current Martian UV environment is still quite severe from a biological viewpoint, we show that substantial protection can still be afforded under dust and ice.