NASA’s mission to Mars launches next year, and it could be our best opportunity yet to discover signs of extraterrestrial life. A pair of new studies have unearthed evidence that Jezero crater—home to a fossilized delta formed by a river that flowed 3.6 billion years ago, and the landing site of the Mars 2020 rover—is home to materials often associated with preserving evidence of ancient life.
Those new findings bolster hopes the 28-mile-wide crater will give us proof that life once existed on Mars, back when it was warm and teeming with liquid water on the surface.
The first study, published November 6 in Geophysical Review Letters, shows the presence of hydrated silica, a mineral that’s exceptionally good at preserving organics and biosignatures in microfossils (those smaller than a millimeter) for several billion years. Any such fossils in Jezero would probably be a few billion years old, says Jesse Tarnas, a planetary scientist at Brown University and the lead author of the new study. “Having a sample of silica that could have formed in a habitable environment increases our chances of finding well-preserved microfossils if life did exist on the surface of Mars,” he says.
Tarnas’s team sifted through data collected by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on NASA’s Mars Reconnaissance Orbiter, launched in 2005 to monitor Mars and study its surface in high detail. He and his colleagues developed and applied a new analytical technique that detects weak electromagnetic signals emitted by minerals on the surface. They found two outcrops of silica deposits situated in Jezero (some at low layers where fossils are more likely to be preserved).
The other paper, published in Icarus on November 12, also used CRISM data to identify deposits of carbonates sitting along the inner rim of Jezero. Carbonates are extremely hardy minerals most often associated with preserving terrestrial fossils of seashells, coral, and stromatolites along shorelines. Concentrated in a “bathtub ring” around Jezero, these newly discovered carbonates may have been deposited by an ancient lake—and could be home to the preserved remains of microbial Martian life.
Briony Horgan, a planetary scientist at Purdue University and the lead author of the new study, is especially hopeful the findings might help us find stromatolites, which are macroscopic mounds made of layers of carbonates and microbes. "These are big enough that they would make a clear target for the rover," she says.
No one is completely sure how the carbonates or the silica deposits got here, but the Mars 2020 rover should be able to easily determine how, when, and where they initially formed. Its SHERLOC instrument, specifically designed to look for signs of extraterrestrial life, is a Raman spectrometer that uses UV laser light to identify organic chemicals. Over its first two years, the rover should be able to explore and study samples of both minerals at their respective locations.
Better yet, even if the rover runs into any walls (literal or otherwise) and fails to determine whether these minerals are associated with ancient Martian life forms, the mission will secure samples for laboratory analysis back on Earth. The silica and carbonate deposits will surely be near the top of the “must return” list.
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