New clues about rainfall on ancient Mars

The Grand Canyon and Mars
The Grand Canyon and Mars

An article published in the journal “Nature Geoscience” describes a research on the possible rainfall that occurred on the planet Mars when it was young. Ramses Ramirez and Robert Craddock, two scientists who have been studying the red planet’s geological and climatic history for years, claim that about 4 billion years ago the climate could be warm and semi-arid with rainfall.

The observations of the last decades conducted with space probes orbiting Mars and rovers / landers on its surface allowed to obtain a considerable amount of information on its geological history that indicate that liquid water for one or more periods could flow when the planet was young. One of the problems is the fact that the many traces found are over 3 billion years old so they also show erosion due to time and traces of various changes occurred over millions of years that are difficult to reconstruct with precision.

One of the great doubts about that ancient era concerns the relationship between the amount of water that was liquid and the amount that was frozen instead. There are researchers who think that the situation was similar to the Earth’s while others think that even when Mars was young water existed above all as ice. Ramses Ramirez from the Earth-Life Science Institute (Tokyo Institute of Technology, Japan) and Robert Craddock from the National Air and Space Museum’s Center for Earth and Planetary Studies (Smithsonian Institution, USA) tried to give an answer.

Robert Craddock already conducted a research on the history of rain on Mars, published in May 2017 in the journal “Icarus”. All the rainfall indicated by its conclusions could exist only if the weather was warm enough for a long time. To understand how this was possible, he worked with Ramses Ramirez, who some years ago developed a climate model in which a greenhouse effect was generated by the volcanic activity existing in that remote era.

In simple terms, the volcanic eruptions that were common 4 billion years ago may have released carbon dioxide, molecular hydrogen and even methane, which as greenhouse gas is much more powerful than carbon dioxide. At the time Mars’ atmosphere was much thicker than today’s, so a greenhouse effect may have allowed a warm, semi-arid climate with episodes of rainfall and liquid water on the surface.

Such rainfall probably dug valleys and other geological features of which there are still traces. According to this reconstruction there could be relatively limited deposits of ice that could melt during summer contributing to the river system.

The image (courtesy Google/Landsat/Copernicus (a) and Google/NASA/JPL/University of Arizona (b). Images adapted from Ramirez and Craddock (2018), Nature Geoscience. All Rights Reserved) shows the Grand Canyon in the USA (a) compared with a dendritic river system on Mars (b). There are small differences that could simply be due to their remarkable age difference.

The research is far from over, also because there are very few traces of the earliest part of Mars’ history, where the conditions that for some time made today’s red planet in many ways similar to the Earth developed. NASA’s InSight mission, with a lander that’s about to be launched to Mars, could help with analyzes focused on Martian geology.

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