The site of a lake more than 3.5 billion years ago, the Jezero Crater has been identified as having distinct deposits of minerals called carbonates along the inner rim.
On Earth, carbonates help form structures that are hardy enough to survive in fossil form for billions of years, including seashells, coral and some stromatolites – rocks formed on this planet by ancient microbial life along ancient shorelines, where sunlight and water were plentiful.
The possibility of stromatolite-like structures existing on Mars is why the concentration of carbonates tracing Jezero's shoreline like a bathtub ring makes the area a prime scientific hunting ground.
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Mars 2020 is NASA's next-generation mission with a focus on astrobiology, or the study of life throughout the universe. Equipped with a new suite of scientific instruments, it aims to build on the discoveries of NASA's Curiosity, which found that parts of Mars could have supported microbial life billions of years ago.
Mars 2020 will search for actual signs of past microbial life, taking rock core samples that will be deposited in metal tubes on the Martian surface. Future missions could return these samples to Earth for deeper study.
Dr Briony Horgan of Purdue University in West Lafayette, Indiana, said, "CRISM [Compact Reconnaissance Imaging Spectrometer for Mars] spotted carbonates here years ago, but we only recently noticed how concentrated they are right where a lake shore would be. We're going to encounter carbonate deposits in many locations throughout the mission, but the bathtub ring will be one of the most exciting places to visit."
In addition to preserving signs of ancient life, carbonates can teach us more about how Mars transitioned from having liquid water and a thicker atmosphere to being the freezing desert it is today.
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Carbonate minerals formed from interactions between carbon dioxide and water, recording subtle changes in these interactions over time. In that sense, they act as time capsules that scientists can study to learn when – and how – the Red Planet began drying out.
Measuring 45 kilometres wide, Jezero Crater was also once home to an ancient river delta. The "arms" of this delta can be seen reaching across the crater floor in images taken from space by satellite missions like NASA's Mars Reconnaissance Orbiter.
The orbiter's Compact Reconnaissance Imaging Spectrometer for Mars instrument, or CRISM, helped produce colourful mineral maps of the "bathtub ring" detailed in the new paper.
Jezero's former lake shoreline isn't the only place scientists are excited to visit. A new study in Geophysical Research Letters points to a rich deposit of hydrated silica on the edge of the ancient river delta.
Like carbonates, this mineral excels at preserving signs of ancient life. If this location proves to be the bottom layer of the delta, it will be an especially good place to look for buried microbial fossils.
The Mars 2020 rover will launch in July or August 2020 from Cape Canaveral, Florida. The Mars 2020 Project at JPL manages rover development for the Science Mission Directorate at NASA Headquarters in Washington.
NASA's Launch Services Program, based at the agency's Kennedy Space Centre in Florida, is responsible for launch management.
Mars 2020 is part of a larger program that includes missions to the moon as a way to prepare for human exploration of the Red Planet. Charged with returning astronauts to the moon by 2024, NASA will establish a sustained human presence on and around the moon by 2028 through NASA's Artemis lunar exploration plans.
The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, leads MRO's CRISM investigation.
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