Evidence For Ancient Wet Martian Environment Hints At Habitats For Life

An artist's impression of what an ancient ocean on Mars might have looked like. NASA/GSFC

Mars wasn’t always so dry and barren – the large fluvial features on its surface betray a past brimming with flowing water. Along with clear evidence of liquid, salty water patches still existing today, evidence of ancient mega-tsunamis has also recently been uncovered. If these were generated by huge impacts, then there had to have been a sizable ocean residing on the surface once upon a time.

Now, a new study published in the Journal of Geophysical Research reveals that iron and calcium-rich carbonate-bearing rocks are fairly widespread on Mars. Carbonate rocks on Earth, such as limestone, form in aquatic, primarily marine environments that contain dissolved carbon. If deposits of Martian carbonates really are as commonplace as this study implies, then the ancient environment on Mars was certainly anything but dry.

“Identification of these ancient carbonates and clays on Mars represents a window into history when the climate on Mars was very different from the cold and dry desert of today,” Janice Bishop, a researcher at the Search for Extraterrestrial Intelligence (SETI) Institute and co-author of the paper, said in a statement.

Wind-formed geological units overlie ancient carbonate-rich rocks (bottom right), excavated up to the surface by impact events. NASA/JPL/University of Arizona

Recent advances in scientists’ understanding of the physical characteristics of geological units mean that the uppermost layers of a planet, be that our own or one of our neighbors, can be analyzed and classified visually without having to visit the surface directly. The Mars Reconnaissance Orbiter (MRO) contains an instrument designed to do exactly that: the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), which uses infrared emissions to identify mineralogical compositions of rocks.

Taking command of this instrument, the team of researchers focused its gaze on the Huygens basin, a massive impact crater 456 kilometers (283 miles) in diameter. The gargantuan depression is pockmarked with plenty of younger craters, many of which were suspected to be ideal sites for finding carbonates. When they were initially formed, it’s likely that the energetic impact would have managed to excavate some buried carbonates up to the surface.

Indeed, the spectral fingerprints of carbonate-bearing rocks were found in the rims of several craters within the Huygens basin, some of which were previously buried at depths of around 5 kilometers (3 miles). Additional carbonate outcrops were found scattered across other parts of the Red Planet, adding credence to the idea that much of the planet once experienced a complex, surface-level hydrogeological system.

This excavation depth indicates that they are fairly ancient, which hints at a wetter past for the region. In fact, the researchers conclude that they date back to the Noachian period, which roughly dates from 4.1 to 3.7 billion years ago, a time period corresponding to a chapter of frequent, powerful impacts in the inner Solar System known as the Late Heavy Bombardment.

The Huygens basin on Mars. The image in the top right shows elevation, with blue being low and red being high. NASA

This period also corresponds to the approximate age of the earliest life on Earth. As far as we know, where there is water, there is life – it doesn’t necessarily require sunlight – so could these carbonates have formed in aquatic environments that also hosted life around the same time?

Sadly, researchers have yet to detect any signs of fossilized or contemporary microbial life on Mars, but anywhere that liquid water exists or once existed aids them in their search for it.

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