Today Mars is a desert. It is a dusty, harsh and pockmarked desert. There is no apparent life on its surface. But over the past few decades, scientists have found evidence of a lost Mars, which looked much more like Earth than hell.
“You can see evidence of what Mars looked like 4 billion years ago,” says NASA astrobiologist Lindsay Hays. Etched into its rocky surface, “you see things like the remnants of a huge river delta,” she says. You see traces of past lakes. It stimulates the imagination. “Maybe there were clouds in the atmosphere,” Hays says. “The surface would have been absolutely stunning.” Past missions to Mars — including with robotic rovers, landers and orbiters — have added on-the-ground evidence that this aquatic past is very likely.
And that’s the most exciting thing for an astrobiologist like Hays: where there was water, there could have been life. “One of the universal characteristics we see of life is that it needs water,” she says. There is a life that survives without light, a life that survives without oxygen. Nothing we know about life without water. If there was water on the surface of ancient Mars, “well, then maybe there was life living in that water,” she says.
A recent episode of Inexplicable – Vox’s podcast that explores big mysteries, unanswered questions and everything in between we learning by diving into the unknown – is about finding a key piece of evidence that would confirm whether there was life on ancient Mars.
Perseverance, NASA’s latest rover to land on the Red Planet in 2021, is currently exploring an ancient dry river delta. The hope is that some form of microbial life that lived – and died – billions of years ago is preserved in its sediments. (It’s less likely to be anything currently living on Mars.) The rover is searching for rock samples that could possibly be sent back to Earth for precise study; they would become the first rocks from Mars sent back to Earth by a scientific mission (we have some samples of rocks from Mars that arrived on Earth via a meteorite).
But… what if we find him? What if evidence of past life on Mars was confirmed?
Finding life on Mars could help us understand just how common life is in the universe
“The reason I’m interested in the search for life has to do with this concept of the interconnectedness of life on Earth,” says Hays.
Two human beings are related by a common ancestor if you look far enough down their family trees. But it is the same for all life. There is a common evolutionary ancestor linking a human to a chimpanzee, a chimpanzee to a frog, a frog to an insect, an insect to a fungus spore. All life on Earth is linked, via the last universal common ancestor (or LUCA), a hypothetical microbe that lived billions of years ago.
For Hays, this relationship raises an epic question.
“So knowing that all life on this planet seems to be related to each other, what would life be like on another planet?” she asks.
It’s possible, though not guaranteed, that if Perseverance finds evidence of past life on Mars, scientists could determine if it likely shares a common ancestor with life on Earth. “All life on Earth shares some similarities,” she says, “using DNA/RNA for ‘information’ storage and most of the same amino acids in their proteins. If we found life on Mars that shared these similarities”, so maybe it’s related to life on Earth.
If life on Earth and Mars have a common ancestor, that means life may have started on one of the planets and then somehow been transported to the other (probably by a meteorite). It’s possible that life didn’t begin on Earth but rather on Mars, or perhaps even elsewhere in space.
But if Martian life looks very different from life on Earth, it could mean that “life is such a fundamental process of the universe that you can have two different life-generating events in the same solar system,” Hays says. This means that life could be even more common in the universe than we currently suspect.
Hays warns that the answers to these epic questions may still elude us, even with the best of all possible rock samples. Scientific evidence is often ambiguous and there will certainly be debate over any radical conclusions.
But the fact remains: Mars is an extremely important place in our solar system to investigate these questions.
And there could be, right now, a single boulder lying on the Martian surface, with epic evidence inscribed on it. Maybe, just maybe, our robot rover will find that rock, pick it up, and show us how special life really is.