Mars microbes may have been able to live deep below the planet's surface
Like, way deep.
Humanity is super-stoked about the idea of finding signs of ancient life on Mars. So much so we keep sending increasingly more advanced machines, like NASA's Perseverance rover, to search for evidence. But we might need to take a much deeper look into the matter, a new study suggests.
A research team led by Rutgers University planetary scientist Lujendra Ojha examined a perplexing problem when it comes to the long-ago habitability of Mars: the paradox of the faint young sun.
The sun wasn't always the perky ball of heat and light we know today. "About 4 billion years ago, the sun was much fainter so the climate of early Mars should have been freezing," Rutgers said in a statement on Wednesday. That's a bit of mystery because we also see lots of signs of water in Mars' past.
Research in recent years has pointed to long-ago liquid water on the Martian surface and even the presence of wild megafloods.
If it were warm and wet, Mars might have been habitable for microbial life. But how do we get meltwater with a faint young sun? The paper from Ojha and his colleagues, published in the journal Science Advances today, addresses this problem.
"I and my co-authors propose that the faint young sun paradox may be reconciled, at least partly, if Mars had high geothermal heat in its past," Ojha said. This is a phenomenon seen on Earth where decaying elements produce heat that can melt ice sheets from below. If Mars experienced similar conditions, that could explain liquid water despite the faint sun.
The study shows that ancient Mars would have been ripe for this sort of heating action 4 billion years ago, but the planet's surface wouldn't have remained very friendly for liquid water thanks to a thin atmosphere and increasingly colder temperatures. "Therefore, life, if it ever originated on Mars, may have followed liquid water to progressively greater depths," Rutgers said.
"At such depths, life could have been sustained by hydrothermal (heating) activity and rock-water reactions," Ojha said. "So, the subsurface may represent the longest-lived habitable environment on Mars."
Our knowledge of Mars and its lineage of water has been expanding at a rapid clip. Recent studies have pointed to hidden ponds of briny water under the Martian polar ice.
Rovers will continue to scour the Martian surface for hints of ancient life, but we may one day want to peer deeper under the planet's skin to fully understand its history of habitability.