The paradoxes of the late Hesperian Mars

The long-standing debate on the existence of ancient oceans on Mars has been recently revived by evidence for tsunami resurfacing events that date from the Late Hesperian geological era. It has been argued that these tsunami events originated from the impact of large meteorites on a deglaciated or nearly deglaciated ocean present in the northern hemisphere of Mars.

Credit : M. Turbet

We show here the annual cumulated rainfall, the annual net surface accumulation of water, and the position of permanent ice reservoirs as simulated with the 3-dimensions Global Climate Model adapted to early Mars environment. We use these simulations to demonstrate that the presence of a deglaciated ocean on late Hesperian Mars should produce fluvial erosion of terrains (of similar age) much more extensively than previously reported in the literature.

--> In this work we show that the existence of a late Hesperian ocean faces a paradox. If cold, the ocean should have been entirely frozen shortly after its formation, thus preventing the formation of tsunami events. If warm, the ice-free ocean should have produced fluvial erosion of Hesperian Mars terrains much more extensively than previously reported.

The climatic impact of Outflow Channels Events on Ancient Mars

~10 years ago, anomalously young 3 billions years old valley networks were observed by the THEMIS camera (on board the Mars Odyssey orbiter) in the Valles Marineris area (ref: Mangold et al. 2004, Science). At the same epoch, huge catastrophic liquid water floods are thought to have carved the large outflow channels visible at the surface of Mars.

Credit : M. Turbet and N. Chaniaud

I simulated the climatic impact of such floods to know if they could be responsible for the formation of the observed valley networks.

I found that the most intense of these events cannot trigger long-term greenhouse global warming, regardless of how favorable are the external conditions (e.g. atmospheric pressure, obliquity and seasons). In any case, outflow channel formation events alone are unable to produce rainfall or significant snowmelt in the regions of interest (e.g. where the late valley networks have been observed).

By Martin Turbet | Design by Andreas Viklund | Inspired by Aymeric Spiga