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On February 18, NASA’s Perseverance rover will parachute through the thin Martian air, marking a new era in the exploration of the red planet. Landing in the Jezero crater, which lies north of the Martian equator, will not be an easy task. Only about 40 percent of missions sent to Mars are successful, according to NASA. If you do, persistence could dramatically change the way we think about extraterrestrial life. That’s because scientists believe that Jezero, a 45-kilometer-wide impact crater that used to be a lake, is an ideal place to look for evidence of ancient microbial life on Mars.
Once it lands, Perseverance will collect and store Martian rock and soil samples, which will eventually be returned to Earth. This is known as a “sample return mission”, an extremely rare type of space exploration mission due to its cost. (In fact, there has never been a sample return mission from another planet.) And once Martian soil is returned to Earth in a decade, scientists will devote themselves to studying the material to find out if there was ever ancient life on Mars.
However, some scientists believe these samples could answer an even bigger question: Did life originate on Earth on Mars?
Although the idea that life began on Mars before migrating to Earth seems like an implausible sci-fi premise, many renowned scientists take the theory seriously. The general idea that life begins somewhere else in space before migrating here also has a name: Panspermia. It is the hypothesis that life exists in other parts of the universe and is distributed by asteroids and other space debris.
To be clear, the notion that life on Earth originates from Mars is not a dominant theory in the scientific community, but it seems to be catching on. And scientists like Gary Ruvkun, a professor of genetics at Harvard Medical School, say it sounds “obvious, in a way.”
The evidence begins with how space debris moved in the young solar system. In fact, we have evidence of an exchange of rocks from Mars to Earth. Martian meteorites have been found in Antarctica and around the world, an estimated 159, according to the International Association of Meteorite Collectors.
“You can assign them to Mars based on the gaseous inclusions they have, which are something like the equivalent of the gases that the Viking spacecraft demonstrated” that exist in the atmosphere of Mars, Ruvkun said. In other words, tiny air bubbles in these rocks reveal that they were forged in Martian air. “So there is an exchange between Mars and Earth – probably more often from Mars to Earth because it goes ‘downhill’, going to Mars is ‘uphill’, gravitationally speaking.”
But for Ruvkun, whose area of expertise is genomics, it is the timing of cellular life that he believes makes a strong case that life on Earth comes from somewhere else, maybe Mars, or maybe Mars vis -a-vis another planet.
Ruvkun pointed out that our genomes reveal the history of life and provide clues about the ancestors that preceded us by millions or even billions of years. “In our genomes, you can see history, right?” he said. “There is the world of RNA that predates the world of DNA and is very well supported by all kinds of biology today, so we know the steps evolution took to get to where we are now.”
Thanks to the advancement of genomics, the understanding of LUCA (the last universal common ancestor), that is, the organism from which all life on Earth evolved, has come a long way. By studying the genetics of all organisms on Earth, scientists have a very good idea of what the single-celled ancestor of all living things (on Earth) was like. They also know the timeline: All modern life forms descend from a single-celled organism that lived about 3.9 billion years ago, just 200 million years after the first appearance of liquid water. In the grand scheme of the universe, that’s not so much.
And the last universal common ancestor was pretty tricky when it comes to organisms. That leaves two possibilities, says Ruvkun. “Either evolution to full modern genomes is really easy, or the reason you see it so fast is that we just ‘captured’ life, it didn’t really start here.” And he adds: “I like the idea of us catching him and that’s why he’s so fast, but I’m an outlier.”
If that’s the case, then Erik Asphaug, a planetary science professor at the University of Arizona, is also an outlier. Asphaug said that what we know about the oldest rocks on Earth, which have chemical evidence for carbon isotopes, dating back almost 4 billion years ago, tells us that life began “to form on Earth almost as soon as possible. happen. “
If that’s the case, it makes an interesting precedent. “Suppose you expect life to flourish every time a planet cools to the point where it can start to have liquid water,” Asphaug said. “But just looking at our own solar system, which planet would likely be habitable first? Almost certainly Mars.”
This is because, Asphaug said, Mars formed before Earth. Early in the history of Mars, when Mars was cooling down, Mars would have had a “hospitable” environment before Earth.
“If life was going to start anywhere, it could start first on Mars,” Asphaug said. “We don’t know what the requirement is, you know, if it required something super special like the existence of a moon or some factors that are unique to Earth, but just in terms of which place had liquid water first, that would have been Mars.” .
Intriguing and compelling evidence relates to how the material moved between the two neighboring planets. In fact, the further you go back in time, the greater the rock collisions between Mars and Earth, Asphaug said. These impact events could have been huge “mountain-sized blocks of Mars” that were launched into space. Such massive asteroids could serve as a home for a resistant microorganism.
“When you hit a planet again, a fraction of that mountain-sized mass is going to survive as debris on the surface,” he said. “It took a while for modeling to show that you can have a relatively intact survival of what we call ‘ballistic panspermia’ – shoot a bullet at one planet, tear it apart, and have it end up on another planet. But it’s doable, we think happens, and the trajectory would tend to go from Mars to Earth, much more likely than from Earth to Mars. “
Asphaug added that surviving the journey, given the vehicle’s mass for the microorganisms, wouldn’t be a problem, and neither would surviving on a new, hospitable planet.
“Any early life form would be resistant to what is happening at the end of the planet’s formation,” he said. “Any organism that is going to exist has to be used to the terrible bombardment of impacts, even apart from this, changing from planet to planet.”
In other words, early microbial life would have been fine with harsh environments and long periods of inactivity.
Harvard professor Avi Loeb told Salon by email that one of the Martian rocks found on Earth, ALH 84001, “did not heat over 40 degrees Celsius throughout its journey and could have carried life.”
All three scientists believe that perseverance could add credibility to the panspermia theory.
“If you were to find remnants of life on Mars, which we hope to do with the Perseverance rover and these other Martian adventures, I would be personally surprised if they weren’t connected at the hip to life on Earth,” Asphaug said.
Ruvkun said he hopes to be one of the scientists to search for DNA when the Mars sample, hopefully, finally returns.
“Launching something from Mars is very difficult,” he said.
But what would this mean for human beings and our existential understanding of who we are and where we come from?
“In that case, we could all be Martians,” Loeb said. He joked that the self-help book “Men are from Mars, Women are from Venus” may have been more right than we think.
Or perhaps, as Ruvkun believes, we are from a different solar system, and life is spreading throughout the universe.
“To me, the idea that it all started on Earth, and each solar system has its own little evolution of life, and they are all independent, it just seems a bit silly,” Ruvkun said. “It’s much more explanatory to say ‘no, it’s spreading, it’s spreading throughout the universe, and we caught it too, it didn’t start here,” he added. “And at this time during the pandemic, what a great time to launch the idea. Maybe people will finally believe it.”
