Is There Life on Mars?

NASA finds tentative evidence of life in Martian samples, but has no way to bring them back yet.

This week, NASA announced that it had discovered a potential biosignature on Mars. Not a sample of life itself, but chemical and geological evidence that life once existed there. The science behind this discover is interesting in itself, but it also features in a wider story about how we do science in space, the shift from government to commercial spaceflight, and the ultimate goal of a human presence of Mars.

A close up of the rock in question. Credit: NASA/JPL

First the details of the discovery itself. The Perseverance rover was landed on Mars over 4 years ago, and is part of a much larger project to investigate the possibility of life on the planet. The sophisticated but limited equipment it carries cannot itself answer the question of whether life is or was present. What it can do is screen candidate samples to find ones which are promising for further investigation.

It has a number of instruments to do this - in this case, it employed a camera, an X-Ray fluorescence instrument and a Raman spectrometer. The latter two work in similar ways, firing a beam of X-rays or an optical laser at a rock and learning something about its composition by what gets re-emitted. Interesting samples are extracted and stored in containers which are then deposited on the Martian surface, to be retrieve by a later sample return mission which will bring them back to Earth for more detailed analysis (more on that later).

The Spots in the Rocks

In a region of the Jezero Crater dubbed Bright Angel, which is lighter and less red than the surrounding Martian surface due to lower amounts of Iron (III) Oxide i.e rust, the Perseverance team found some unusual features in mudstone which had been deposited billions of years ago when surface water still flowed on Mars. These were dark spots, a fraction of a millimetre in diameter, called “poppy seeds” and slightly larger features about a millimetre across called “leopard spots” that had a dark rim and a lighter core.