The Best Evidence for Life on Mars Might be Found on its Moons

The search for Martian life has been ongoing for decades.  Various landers and rovers have searched for biosignatures or other hints that life existed either currently or in the past on the Red Planet.  But so far, results have been inconclusive.  That might be about to change, though, with a slew of missions planned to collect even more samples for testing.  Mars itself isn’t the only place they are looking, though. Some scientists think the best place to find evidence of life is one of Mars’ moons. 

Phobos and Deimos are usually an afterthought when discussing Mars exploration priorities, but interest has been growing recently due to their unique place in the overall Martian system.  They might serve as a depository for material that was blasted off of Mars’ surface in the past.

Many scientists think that early Mars could have been habitable, with temperatures in a biologically suitable range, an atmosphere that hadn’t yet been stripped away, and liquid water flowing on its surface, some of which formed Jerezo Crater, where Perseverance is now exploring.  If any life existed back in these more hospitable conditions, it would have been subjected to the catastrophes commonly thought of as extinction-level events here on Earth – asteroid impacts.

Asteroid impacts were much more common earlier in the solar system’s formation, ejecting a multitude of the Martian regolith into space.  While some of that ejecta takes the form of meteorites that eventually wind up on Earth, a large amount of it is absorbed by the moons, particularly Phobos.  Scientists estimate that over 1 billion kg of ejected material was deposited relatively evenly across Phobos’ surface, making up over 1000 parts per million of the material on the small moon. 

The moon itself is incapable of supporting life – it has no water to speak of and is constantly irradiated by the sun and more general cosmic rays.  No life could survive on its surface, yet searching for life on Phobos still has some major advantages over searching for life on Mars itself.

While Mars doesn’t have a traditional weather cycle, like Earth’s, its surface changes regularly, with dust storms and wind causing the erosion and deposition of long-standing geological edifices.  However, both Martian moons lack any such system, so any biosignature that landed there from an asteroid impact would likely still be in the same position now, and in much the same shape it would have been in when it was blasted in space.

This is all great in theory, but getting data to prove that theory is another matter entirely.  Luckily there are a series of missions in the works to attempt to do so.  The Mars Sample Return mission (MSR) is ongoing, and Perseverance’s jaunt in Jezero Carter is the first step. The Japanese Space Agency’s Mars Moons eXploration (MMX) mission plans to return to Earth with a regolith sample from Phobos in 2029.

Another advantage that MMX would have over the MSR is that the debris spread across Phobos’ surface wouldn’t be specific to a particular area on Mars, unlike the samples of Jezero that Perseverance is currently attempting to collect. Asteroid impacts are equally destructive ejecta creators, so if life happened to spring up only in a certain region of Mars, it would be more likely to have been caught in an asteroid impact and partially deposited on Phobos. There’s a much better chance of scientists finding that evidence there than of them luckily choosing the right area to look in with no previous knowledge.

No matter where they look, and no matter what they find, scientists working on both the MSR and MMX missions will be adding valuable knowledge to humanity’s stockpile.  And if they happen to find evidence of one of the most important discoveries in history, so much the better.

Learn More:
Science – Searching for life on Mars and its moons
Inverse – THE BEST PLACE TO FIND MARTIAN LIFE MIGHT NOT BE ON MARS AT ALL
The Independent – Martian moon Phobos could be home to extinct alien life from an ancient lake, new Jaxa study suggests
Digital Trends – To find evidence of life on Mars, we should look to its moon Phobos

Lead Image:
Image of Mars’ moon Phobos
Credit – MRO / NASA