Scientists urge caution about mystery Mars rock found by NASA rover

NASA has announced the first detection of possible biosignatures in a rock on the surface of Mars.

NASA has announced the first detection of possible biosignatures in a rock on the surface of Mars. The rock contains the first martian organic matter to be decisively detected by the Perseverance rover, as well as curious discoloured spots that could indicate the past activity of microorganisms.

Ken Farley, project scientist on the mission, has called this “the most puzzling, complex, and potentially important rock yet investigated by Perseverance”.

Perseverance is part of Mars 2020, the first mission since Viking that is explicitly designed to seek life on Mars (officially, to “search for potential evidence of past life using observations regarding habitability and preservation as a guide”). Arguably, that objective has now been achieved: potential evidence for past life has been found. But much more work is needed to test this interpretation of the data. Here’s what we do know.

Since landing in Jezero crater a few years ago, Perseverance has traversed a series of rocks formed nearly four billion years before present. Mars back then was far more habitable than the cold, dry, toxic red planet of today.

There were thousands of rivers and lakes, a thick atmosphere, and comfortable temperatures and chemical conditions for life. Many of the rocks in Jezero are sedimentary: mud, silt and sand dumped by a river flowing into a lake.

The new discovery concerns one of these rocks. Informally named “Cheyava Falls” (a waterfall in Arizona), it is a small reddish block of what looks like a mudstone, enriched with organic molecules. The rock is also laced with parallel white veins. Between the veins are millimetre-scale whitish spots with dark rims. For an astrobiologist, all these features are intriguing. Let’s take them one-by-one.

First, “organic molecules”, are made of carbon and hydrogen (commonly with sulphur, oxygen or nitrogen as well). Examples include the proteins, fats, sugars, and nucleic acids from which all life as we know it is constructed.