It’s one of our great cosmic misfortunes that we entirely missed Mars’ golden age. About 3.5 billion years ago—during the first billion or so years of the solar system’s existence—the Red Planet was a blue planet, awash in ocean, seas, and rivers the way Earth is today. Ancient sedimentary basins, deltas and riverbeds are all that is left of Mars’ watery past—which ended when the planet’s magnetic field shut down, allowing the solar wind to claw the atmosphere away and the water to sputter into space.
But a lot could have happened in those first one billion years—including the emergence of life. On Earth, life got started well before the planet’s billionth birthday, leading many exobiologists—scientists who study the possibility of extraterrestrial life—to believe that anywhere there is liquid water and the proper chemistry, biology can quickly take hold.
“Life on Earth got started very quickly,” astronomer Seth Shostak of the SETI (Search for Extraterrestrial Intelligence Institute) once told me. “That’s like walking into a casino in Vegas, pulling the handle and winning the jackpot. You say, ‘Well, either I’m very, very lucky or this is not a difficult bet.’”
The Perseverance rover first landed on Mars in February 2021. And this week, as NASA reports, the rover collected new evidence that that bet may have paid off on Mars too. In late July, Perseverance abraded some samples from a formation in Mars’ Jezero crater that astronomers have dubbed Wildcat Ridge—a sedimentary rock about 3 ft. wide that formed more than three billion years ago as the saltwater lake that once filled the crater began to evaporate and fine sand and mud began to settle out.
Studying the samples with an onboard instrument dubbed SHERLOC—Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals—Perseverance has now found organic chemistry in the ancient mud, including the presence of carbon, hydrogen, and nitrogen; further analysis may also turn up nitrogen, phosphorus and sulfur. All of these ingredients are present in biologically rich environments on Earth.
“In the distant past, the sand, mud, and salts that now make up the Wildcat Ridge sample were deposited under conditions where life could potentially have thrived,” said Perseverance project scientist Ken Farley of Caltech in Pasadena, California, in a statement. “The fact the organic matter was found in such a sedimentary rock—known for preserving fossils of ancient life here on Earth—is important.”
That’s the good news. The less good news—or at least the less immediately gratifying—is that it will be a long while before scientists can learn if the ingredients of Martian biology actually signify the long-ago (or even extant) presence of Martian biology. Perseverance’s suite of instruments are limited in what they can study and in order to look for such slam-dunk proof as ancient micro-fossils, the samples the rover collects must be studied up close by scientists in a lab.
For that reason, the rover is equipped with 43 titanium sample tubes in which it is caching the Martian soil and rock it is studying. So far, a dozen of the tubes have been filled and sealed, and all of them will eventually be deposited at a well-marked spot on the Martian surface. As early as 2028, NASA and the European Space Agency (ESA) will launch a Mars Sample Return Mission, in which a lander will collect the tubes, blast back off the surface of Mars and transfer them to an orbiter that will carry them home.
NASA’s long-term goal, of course, is to have humans on Mars who can do this kind of work more easily and in situ. But the key here is the “long-term” factor. Don’t look for boot prints on Mars until the mid 2030s or even later. In the meantime, the sample-return scenario is our best bet for finding out if our once-watery planetary neighbor was a once-living neighbor too. Perseverance’s just-announced discovery raises the possibility—at least a little—that the answer to that question could be yes.
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