If life ever existed near the surface of Mars, microbes could have survived by following the water down through the crust. That would require habitable conditions to have stretched to great depths for at least some time. To serve as a habitat, rocks in the mid-crust would also need to host organic molecules and a source of energy.
Unfortunately, it’s doubtful scientists will be able to plumb these depths anytime soon.
“It would be very challenging,” Wright said. Only a few projects have ever bored so deep into Earth’s crust, and each one was an intensive undertaking. Replicating that effort on another planet would take lots of infrastructure, Wright goes on, and lots of water.
But there may be other ways to find out more. If groundwater on Mars has been pushed to the surface in certain places, exploring them could provide a window into the environment underground. Future missions like Mars Sample Return could also drastically change what we know about the history of Mars and its water.