'Habitable zone' on Mars could be just right for life

Everybody from NASA to David Bowie has wondered if there’s life on Mars – and now we might have a precise place to look for it. A new Caltech study has shown that photosynthetic microbes could thrive in a small habitable zone beneath the ice.

As any Martian rover will tell you, the surface of the Red Planet is a cold, barren wasteland. The missing ozone layer and magnetic field means ultraviolet radiation from the Sun is about 30% stronger than on Earth, sterilizing those dusty red rocks.

But overwhelming evidence suggests that wasn’t always the case – billions of years ago Mars may have had rivers, lakes and even oceans, which could have housed life. As those favorable conditions dried up, any microbial life that had evolved could have retreated underground for shelter, where there may still be enough nutrients and resources today. Now, scientists from Caltech have calculated a potential habitable zone for subterranean microbes on Mars.

Habitable zones are essentially places where conditions are just right for life to survive. Astronomers often talk about them on the scale of solar systems – Earth, for example, is right in the habitable zone around the Sun, where temperatures are not too hot and not too cold, so liquid water can pool on the surface.

In the context of Mars, a habitable zone for photosynthesizing microbes could exist beneath a certain amount of ice. Too shallow and the strong ultraviolet radiation will cook them, but too deep and there won’t be enough visible light filtering down for them to feed on.

The Caltech team calculated how far down this habitable zone would be, based on the dust content and structure of the ice. If dust makes up more than about 1% of the ice, it would be too shaded for life to survive – but in ice containing between 0.01 and 0.1% dust, microbes could find refuge at depths between 5 and 38 cm (2 and 15 in). If the ice is even cleaner, a potential habitable zone could extend as deep as 2.15 to 3.1 m (7.05 to 10.17 ft).

Liquid water would still be necessary for this kind of life, but the team says that dust particles trapped in the ice would occasionally cause small pockets of localized melting that could meet their needs. This process wouldn’t work too close to the Martian poles, but would be possible in ice elsewhere on the planet.

Of course, just because it’s theoretically possible for life to exist in these areas, doesn’t mean that it definitely does. But the study does give future robotic or crewed missions to Mars a good place to start looking.

The research was published in the journal Nature Communications Earth & Environment.

Source: Caltech via Scimex