NASA rover searching for rocks reveals startling geology of Martian crater

By Will Dunham

WASHINGTON (Reuters) – Core samples drilled by NASA’s Perseverance rover on the surface of Mars reveal the geology of a gaping crater that scientists suspect harbored microbial life billions of years ago, including surprises about the nature of the rock found there.

The samples, obtained by the six-wheeled, car-sized robotic rover and stored for future transport to Earth for further study, showed that rock at four sites inside Jezero Crater is igneous – formed by the cooling of molten materials. The rocks also bore evidence of weathering from exposure to water, another sign that cold, arid Mars was long ago hot and humid.

Scientists had thought that the rock, formed around 3.5 billion years ago, might be sedimentary, formed from mud and sand deposited in a lake bed.

“In fact, we found no evidence of sedimentary rocks where the rover explored the floor of the crater, despite the fact that we know the crater once contained a lake and that sediment must have been deposited. These sedimentary deposits must have eroded,” said Caltech geochemist Kenneth. Farley, lead author of one of four studies published in the journals Science and Science Advances describing the geology of the crater.

Perseverance arrived on Mars in February 2021 and has been working in Jezero Crater ever since, using a suite of instruments, as scientists investigate whether Earth’s closest planetary neighbor ever possessed conditions conducive to life.

It collects rock samples, the size of blackboard chalk, in small tubes to be picked up by a spacecraft in 2033 and brought to Earth for further examination, including for biosignatures – indicators of life .

The Jezero crater is 45 km wide and is located just north of the Martian equator. It appears that the area was once abundant in water and hosted a river delta, with river channels overflowing the crater wall to form a large lake. Scientists suspect the crater could have harbored microbial life, with evidence possibly contained in the lake bed or shoreline rock.

Perseverance is now collecting samples in the delta region.

The igneous rocks in the crater were found to have interacted with water, producing new minerals and depositing salts, although this water was apparently in low abundance or not present for very long – probably groundwater. But the presence of the water suggests it might have been a habitable environment at the time, the researchers said.

“We have collected samples that will be sent back to Earth, and they should provide critical evidence of the types of organisms, if any, that inhabited the rocks at the bottom of Jezero Crater as they interacted with water,” he said. Yang Liu, planetary sample scientist at NASA. Jet Propulsion Laboratory and lead author of one of the studies.

The four samples were drilled in two zones, one called Seitah and the other Maaz. The Seitah rock appears to have been formed underground by the slow cooling of a thick layer of magma. Maaz rocks may have cooled relatively faster in an upper layer of subterranean magma or after a surface volcanic eruption. Either way, any rock layers that once covered these areas have since eroded away, whether from water or wind.

Liu said the Seitah samples were a coarse-grained igneous rock containing the mineral olivine, noting that three Martian meteorites found on Earth have a similar composition.

Examining samples on Earth can reveal when the rock formed and give a firmer answer to when liquid water existed on the Martian surface. Liquid water is a key ingredient for life.

“Understanding when and for how long climatic conditions on Mars allowed liquid water to be stable is critically important to the larger questions we are trying to address with this mission and sample return – at find out if and when life might have once existed in early Mars, billions of years ago,” said geochemist and study co-author David Shuster of the University of California, Berkeley.

(Reporting by Will Dunhamk, editing by Rosalba O’Brien)

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