Low HesperianP_CO2constrained from in situ mineralogical analysis at Gale Crater, Mars

Abstract

Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planetwide evidence of liquid water in the Noachian and Early Hesperian. In this study, we use mineral and contextual sedimentary environmental data measured by the Mars Science Laboratory (MSL) Rover Curiosity to estimate the atmospheric partial pressure of CO 2 (P CO2 ) coinciding with a long-lived lake system in Gale Crater at ∼3.5 Ga.A reaction-transport model that simulates mineralogy observed within the Sheepbed member at Yellowknife Bay (YKB), by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicates atmospheric P CO2 levels in the 10s mbar range. At such low P CO2 levels, existing climate models are unable to warm Hesperian Mars anywhere near the freezing point of water, and other gases are required to raise atmospheric pressure to prevent lake waters from being lost to the atmosphere. Thus, either lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climate models still lack an essential component that would serve to elevate surface temperatures, at least locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO 2 in inferred warmer conditions and valley network formation of the late Noachian.Hesperian Mars | martian atmosphere | Mars Science Laboratory | Gale Crater | carbon dioxide M ore than four decades of orbital imaging of Mars provide geomorphological evidence of a more active hydrological cycle and larger inventory of water during the Noachian and Early Hesperian (1, 2). The widespread distribution of hydrous clay minerals in martian terrains of this age and their subsequent demise provide pivotal supporting evidence (3, 4), but the clay mineral-bearing deposits also present a paradox in that carbonate minerals, expected coprecipitates in surficial settings in communication with a CO 2 -bearing atmosphere, are typically absent (5). Atmospheric reconstructions using carbon isotopic measurements and global inventories of martian carbon also indicate 100s mbar CO 2 levels (5, 6). This leads to the question of how the surface of ancient Mars, faintly heated by a young sun, was kept warm enough to allow an active hydrological cycle, without substantial amounts of a key greenhouse gas in the atmosphere. However, the breadth of available constraints on carbon sinks (6) and potential clay mineral formation in subsurface settings uninfluenced by the atmosphere (7) introduce uncertainties to estimates and the periods to which they apply. In this work we use mineralogical and sedimentological data from ∼3.5 Ga martian lake sediments to obtain a reference point for the evolution of martian P CO2 .During its traverse to the lower slopes of Aeolis Mons (informally known as Mt. Sharp), the MSL team documented a ∼70 m sedimentary section of mudstones, siltstones, sandstones, and conglomerates deposited by lakes and rivers on the floor of Gale c...

Abiotic Input of Fixed Nitrogen by Bolide Impacts to Gale Crater During the Hesperian: Insights From the Mars Science Laboratory

“…Several data points fall below the lower predicted boundary by bolide impacts under this condition. This could indicate that nitrogen fixation by bolide impacts took place in an atmosphere without H 2 and a CO 2 /(CO 2 + N 2 ) ratio greater than 0.75 or lower than 0.4 resulting in a reduction in the rate of nitrogen fixation (see section ) as documented for the lack of CO 3 2− in the sedimentary rocks found in Gale crater (Bristow et al, ). The value obtained from the Cumberland sample is greater than the maximum predicted value for bolide impacts.…”

“…As the CO 2 levels dropped below 1 bar, climate models that consider only CO 2 and water are incapable to heat up the Noachian and Hesperian periods in the proximity of the freezing point of water (Wordsworth, ). Furthermore, geochemical evidence from sedimentary rocks in Gale crater reveals aqueous alteration but a lack of CO 3 2− minerals, suggesting very low levels of CO 2 (0.01–0.1 bar) at the time of deposition, around 3500 Myr ago (Bristow et al, ). A possible solution for the Martian climate puzzle is the presence of 10–20% molecular hydrogen (H 2 ) from volcanic emissions that would have warmed the atmosphere episodically by collision‐induced absorption with CO 2 (Ramirez et al, ; Sagan, ; Wordsworth et al, ) or N 2 (Wordsworth & Pierrehumbert, ).…”

Experimental hydrothermal alteration of basaltic glass with relevance to Mars

“…), (2) deep crustal sequestration (Edwards and Ehlmann ), or (3) too low partial pCO 2 pressures (Bristow et al. ).…”

“…; Bristow et al. ), but mean surface temperatures reaching 273 K may be possible assuming an atmosphere having CO 2 pressures of 1.25–2 bar and 2–10% CH 4 or H 2 (Wordsworth et al. ).…”

Mars Climate History: Insights From Impact Crater Wall Slope Statistics

“…One interpretation is the presence of a relatively warmer climate at lower altitudes. Bristow et al (2017) have analyzed the mineralogy of the fluvio-lacustrine deposits in Gale crater and inferred an upper limit of the partial pressure of CO 2 in the atmosphere of tens of mbar. For a denser atmosphere (above~100 mbar, Wordsworth et al, 2013) the atmospheric lapse rate causes elevational zonality of the surface temperature.…”