Abstract
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. Here we show that the presence of such a late 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. To solve this apparent paradox, we suggest a list of possible tests and scenarios that could help to reconcile constraints from climate models with tsunami hypothesis. These scenarios could be tested in future dedicated studies.
Highlights
The existence of liquid water oceans on ancient Mars has long been a topic of debate[1,2,3,4,5,6] and has strong implications for the search for life in the solar system
The overlap of several distinct lobate deposits as well as their wide range of elevation suggest the possibility of multiple tsunami events[7,8]. Both studies[7,8] reported that these tsunami events were likely caused by the collision of large meteorites (3–6 km in diameter) on an ice-free or sea-ice covered ocean located in the northern lowlands of Mars
Sustaining a liquid-water ocean, even ice-covered, would require a very strong greenhouse effect involving a mixture of greenhouse gases. 3-D climate modeling of early Mars under an atmosphere composition of only CO2 and H2O, performed with a water cycle that includes water vapor and clouds, is unable to maintain significant amount of liquid water anywhere on the red planet, even when maximizing the greenhouse effect of H2O and CO2 ice clouds[9,10]
Summary
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. The ice-free ocean should have produced fluvial erosion of Hesperian Mars terrains much more extensively than previously reported. To solve this apparent paradox, we suggest a list of possible tests and scenarios that could help to reconcile constraints from climate models with tsunami hypothesis. The overlap of several distinct lobate deposits as well as their wide range of elevation suggest the possibility of multiple (at least two) tsunami events[7,8] Both studies[7,8] reported that these tsunami events were likely caused by the collision of large meteorites (3–6 km in diameter) on an ice-free or sea-ice covered ocean located in the northern lowlands of Mars. We discuss the implications of the presence of a deglaciated (or nearly deglaciated) ocean on both the atmosphere and the geology of Late Hesperian Mars
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