NASA's Perseverance rover has spotted a thin, smooth, purple coating on some stones on Mars, which could hold clues to the planet’s potential for ancient life.
Red dust paints Mars in ruddy hues, from the surface to the skies. But NASA's Perseverance rover has spotted swaths of another colour among the rusty shades. At nearly every site the robotic geologist visits, the Martian palette includes purple.
The colour forms a thin, smooth coating on some stones, and it leaves paint-like blobs on others. Still other rocks look as if they've been partially frosted in magenta icing, says Ann Ollila, a geochemist at Los Alamos National Laboratory who presented an early analysis of the coatings at a recent conference of the American Geophysical Union (AGU).
The colour touches rocks of all different shapes and sizes—even tiny pebbles haven't escaped the pops of purple. But how, exactly, did these coatings form? "I don't really have a good answer for you," Ollila says.
Scientists are eager to know more. "There's a lot to look forward to as we continue to do analyses," says Nina Lanza, the team lead for Space and Planetary Exploration at Los Alamos National Laboratory, who has been studying the coatings alongside Ollila.
The origin of the mysterious splotches could help reveal clues about Mars's past, including whether it might have hosted ancient life. As the coatings formed, they could have encoded information about the surrounding conditions in their chemical and mineral makeup, helping scientists reconstruct environments now long gone. They also could hold more direct evidence of life: On Earth, microbes help craft many similar stony veneers.
The purple Martian coatings were found in Jezero crater, a 28-mile-wide pockmark blasted out by a meteorite impact billions of years ago that once hosted an ancient lake. Perseverance landed in the crater in February 2021 and has since been roaming across it. At almost every stop along the rover's route, flashes of purple have popped up in its images.
Early analyses point to the presence of hydrogen and oxides, suggesting water played a role in the the purple patches' formation. But so far, the team has only analysed a few samples, and they are still contending with many challenges. For example, separating the chemical signatures of the coatings, the underlying rock, and the ever-present dust on the Martian surface is complex.
The team hopes to further untangle the chemistry of the coatings and search for organic matter associated with the Martian crusts, which could hint at the presence of microbes. But getting the rocks back to Earth for lab analysis is one of the few ways to definitively pin down how the patches formed.
From an article by Maya Wei-Haas for National Geographic.