DIX Planetary Science Seminar
Characterization of the habitability on ancient Mars is a central endeavor of planetary science, and it has been approached from the perspectives of geology and climate science, but the evolution from the paleo-atmosphere and climate to the modern one remains unclear. The isotopic compositions of the present-day atmosphere, as well as the extent of carbonate, nitrate, and hydrated rocks, carry signatures of past evolution. We have developed a new model to trace the atmospheric evolution caused by outgassing, escape to space, and sequestration into the crust. Recognizing that the model has many parameters, we have used the Markov Chain Monte Carlo method to reveal the solution ensemble permitted by the isotopic compositions of the atmosphere and the size of crustal volatile reservoirs. Most of the evolutionary solutions feature gradual descent of the partial pressure of N2 and Ar, resulting in the possibility to derive the paleo-atmospheric conditions by present-day measurements. The ensemble points to an atmosphere of 0.3 – 1.5 bar CO2 and 0.1 – 0.5 bar N2 in the late Noachian when most valley networks formed. Also, ocean-scale volumes of water on ancient Mars are simultaneously compatible with widespread hydrated minerals, H escape rate estimates, and D/H measurements. These constraints collectively indicate a CO2-N2-H2 atmosphere in the late Noachian, provide a framework to explain the geologic records that suggest intermittent conditions for liquid water on ancient Mars, and guide future explorations.