On our planet, the remains of the first forms of life have almost entirely disappeared. But on Mars, cold and dry, they could be buried under a few inches of earth.
A little over a month ago, Perseverance successfully landed on Mars. Since then, the teams have been working to check the rover’s instruments. Researchers are now preparing for his next big mission step: to fly Ingenuity. Once this flight is over, Perseverance will dive seriously into its scientific work aimed at looking for traces of past life. And if NASA has focused on Mars to try to answer this existential question: “are we alone in the Universe?”, There are good reasons.
Two old binoculars
Early in the history of the solar system, Earth and Mars were remarkably similar. Four and a half billion years ago, the two planets bubbled with magma before cooling into rocky crusts, filled with water and geological activity.
While on Earth chemistry gave way to biology, Mars was an equally friendly environment. Liquid water in fact roamed its surface, protected by a magnetic field generated by the core of the planet. On the other hand, Martian volcanoes projected greenhouse gases into the atmosphere, enveloping the planet in a beautiful blanket of heat.
Today, Mars shows a completely different face, at the same time very cold and very dry. Yet this inhospitable desert appears to be the perfect place to discover traces of life, according to Dr Sarah Johnson of Georgetown University, who worked on NASA’s Opportunity, Spirit and Curiosity rover teams.
Mars in Antarctica
Back in 2017. Sarah Johnson joined with her team the McMurdo station, in Antarctica, installed on the slopes of Mount Boreas. You will find it in theOlympus range, a windswept and mostly ice-free mountain range. Instead: silt, sand and some rocks. Its top is one of the most Mars-like places on our planet.
As the team crosses this desolate expanse, Dr. Johnson then notices an area where the ground feels lighter. “There, under a pristine layer of ashes, were the preserved remains of another world. 14 million years ago, before Antarctica turned into a polar wasteland – there had been a lake. For thousands of years, it occupied the place where I stood, just under the soles of my boots ”, she writes.
Sarah Johnson then puts on a sterile coveralls and gloves to take a few samples that look suspiciously like “tufts of human hair”. Back at the McMurdo station laboratory, she opens a small sterile tube to slip in these relics from the past, taking care to isolate one of these strands of material in passing and place it in an empty Petri dish.
And there…. surprise! “When I added a drop of water, the sample quickly started to rehydrate. Almost all of the plants and animals that once inhabited the interior of Antarctica are gone, but there, in the palm of my hand, I could see the tiny leaves of ancient bryophytes ”.
Fascinated, Sarah Johnson then passes the sample under a microscope. “The depth and detail were extraordinary, accentuating the beauty of these organisms which had lived their lives on an immensely different continent”.
If life exists on Mars, it might just be “under our feet”
Nowhere else on Earth would these samples have been so wonderfully preserved as they were in Antarctica, locked in a dry, deep frost. In a tropical or temperate environment, the carbon bonds would have given way quickly. Just as heat and water can allow life to flourish, these two factors can also promote its decomposition and disintegration.
This experience therefore brings us back to that cold, dry and unchanging place that is the Jezero crater. Naturally, Perseverance is unlikely to stumble upon a life form as complex as a bryophyte, but perhaps he can isolate traces of an ancient microbial ecosystem.
On Earth, these remains of life would have been buried long ago due to plate tectonics, but the Red Planet lacks them. If life has ever flourished here, and left its mark, then it might just be right under its wheels.