A lower limit of atmospheric pressure on early Mars inferred from nitrogen and argon isotopic compositions

Abstract

We examine the history of the loss and replenishment of the Martian atmosphere using elemental and isotopic compositions of nitrogen and noble gases. The evolution of the atmosphere is calculated by taking into consideration various processes: impact erosion and replenishment by asteroids and comets, atmospheric escape induced by solar radiation and wind, volcanic degassing, and gas deposition by interplanetary dust particles. Our model reproduces the elemental and isotopic compositions of N and noble gases (except for Xe) in the Martian atmosphere, as inferred from exploration missions and analyses of Martian meteorites. Other processes such as ionization-induced fractionation, which are not included in our model, are likely to make a large contribution in producing the current Xe isotope composition. Since intense impacts during the heavy bombardment period greatly affect the atmospheric mass, the atmospheric pressure evolves stochastically. Whereas a dense atmosphere preserves primitive isotopic compositions, a thin atmosphere on early Mars is severely influenced by stochastic impact events and following escape-induced fractionation. The onset of fractionation following the decrease in atmospheric pressure is explained by shorter timescales of isotopic fractionation under a lower atmospheric pressure. The comparison of our numerical results with the less fractionated N ( 15 N/ 14 N) and Ar ( 38 Ar/ 36 Ar) isotope compositions of the ancient atmosphere recorded in the Martian meteorite Allan Hills 84001 provides a lower limit of the atmospheric pressure in 4 Ga to preserve the primitive isotopic compositions. We conclude that the atmospheric pressure was higher than approximately 0.5 bar at 4 Ga.

Climate Simulations of Early Mars With Estimated Precipitation, Runoff, and Erosion Rates

“…The baseline ocean of Di Achille and Hynek (2010) (light blue shaded region) was assumed in these calculations. Craddock & Lorenz, 2017;Hu et al, 2015;Kite et al, 2014;Kurokawa et al, 2018) (Figure 5a). These numbers also corroborate recent results from 1-D RC climate modeling (Ramirez, 2017;Wordsworth et al, 2017).…”

Survivability of Soil and Permafrost Microbial Communities after Irradiation with Accelerated Electrons under Simulated Martian and Open Space Conditions

“…Laboratory experiments do not allow for studying the long accumulation of doses of relatively low intensity in the microbial biomass of natural soil. The main question of the present study is how long the biosphere of Mars could be maintained after the supposed catastrophic change in planetary conditions [24][25][26][27][28][29], the gradual loss of the atmosphere [30], and the formation of a modern climate.…”

Geologic Constraints on Early Mars Climate

“…Meteorite noble gas data have been interpreted to require P > 0.5 bar at ~4.1 Ga, but also P < 0.4 bar at ~4.1 Ga (Cassata et al 2012, Kurokawa et al 2018). (Manga et al 2012; single data point); (6) modern atmosphere; (7) modern atmosphere + buried CO2 ice; (8*) meteorite trapped-atmosphere isotopic ratios (Kurokawa et al 2018); (9 -range spanned by brown dashed lines) modern escape-to-space measured by Mars Atmosphere and Volatile Evolution Mission (MAVEN) and Mars Express (MEX) spacecraft, extrapolated into past (Barabash et al 2017, Lillis et al 2017, Brain et al 2017, Ramstad et al 2018); (10*) bedform wavelengths (Lapôtre et al 2016). Approximate and model-dependent implications for climate are shown by background colours.…”