CO₂-SO₂ clathrate hydrate formation on early Mars

¹ Univ Paris-Sud, UMR IDES, Université Paris-Sud & CNRS, Bât. 504, Orsay, F-91405, France
² IAS, Université Paris-Sud, CNRS, France
³ Centre SPIN, ENS des Mines de Saint-Etienne, France
⁴ Center for Earth System Sciences, Tsinghua University, Beijing, China
⁵ Institut UTINAM, East-Lansing, UMR 6213, Université de Franche-Comté, France
⁶ Université de Toulouse; UPS-OMP; CNRS-INSU; IRAP; Toulouse, France

Abstract

Most sulfate minerals discovered on Mars are dated no earlier than the Hesperian. We showed, using a 1-D radiative-convective-photochemical model, that clathrate formation during the Noachian would have buffered the atmospheric CO₂ pressure of early Mars at ~2 bar and maintained a global average surface temperature ~230 K. Because clathrates trap SO₂ more favorably than CO₂, all volcanically outgassed sulfur would have been trapped in Noachian Mars cryosphere, preventing a significant formation of sulfate minerals during the Noachian and inhibiting carbonates from forming at the surface in acidic water resulting from the local melting of the SO₂- rich cryosphere. The massive formation of sulfate minerals at the surface of Mars during the Hesperian could be the consequence of a drop of the CO₂ pressure below a 2-bar threshold value at the late Noachian-Hesperian transition, which would have released sulfur gases into the atmosphere from both the Noachian sulfur-rich cryosphere and still active Tharsis volcanism. Our hypothesis could allow to explain the formation of chaotic terrains and outflow channels, and the occurrence of episodic warm episodes facilitated by the release of SO₂ to the atmosphere. These episodes could explain the formation of valley networks and the degradation of impact craters, but remain to be confirmed by further modeling.