Samples drilled by NASA’s Perseverance spacecraft on the surface of Mars are revealing the geology of a crater that scientists suspect may have harbored microbial life billions of years ago, including surprises about the nature of the rock there.
The samples, taken by the car-sized six-wheel robot and stored for future transport to Earth for further study, showed that rocks from four locations inside Jezero Crater are igneous — formed by cooling molten material. The rocks also show evidence of alteration by exposure to water, another sign that the cold, arid planet Mars was hot and wet long ago.
Scientists had thought that the rock, formed approximately 3.5 billion years ago, might be sedimentary, formed as mud and sand deposited on a lake bed.
“Actually, we found no evidence of sedimentary rocks where the probe explored the crater floor, despite the fact that we know that the crater once housed a lake where sediments must have been deposited. These sedimentary deposits must have eroded away,” said the geochemist. Caltech’s Kenneth Farley, lead author of one of four studies published in Science and Science Advances that describe the crater’s geology.
Perseverance arrived at Mars in February 2021 and has been actively working on the Jezero crater ever since, using a suite of instruments, as scientists investigate whether Earth’s closest neighboring planet once had conditions conducive to life.
She is collecting samples of rocks, the size of chalk on a blackboard, in tiny tubes to be retrieved by a spacecraft in 2033 and brought back to Earth for further examination, including for biosignatures — indicators of life.
The Jezero Crater is 45 km wide and is located north of the Martian equator. It appears that the area once had abundant water and was home to a river delta, with river channels spilling over the crater wall to form a large lake. Scientists suspect the crater could have harbored microbial life, with evidence perhaps contained in the lake bed or rocks along the shores.
Perseverance is now taking samples in the delta area.
The igneous rocks in the crater were found to interact with the water, producing new minerals and depositing salts, although this water was apparently not very abundant or had not been present for a long time—probably groundwater. But the presence of water suggests this may have been a habitable environment at the time, the researchers said.
“We have collected samples that will be returned to Earth, which should provide critical evidence of what types of organisms, if any, inhabited the rocks at the bottom of Jezero Crater when they interacted with water,” said Yang Liu, a planetary sampling scientist at the NASA Jet Propulsion and lead author of one of the studies.
The four samples were obtained by drilling in two areas, one called Seitah and the other, Maaz. The Seitah rock appears to have formed underground by the slow cooling of a thick layer of magma. Maaz rocks may have cooled relatively faster in an upper layer of underground magma or after a volcanic eruption on the surface. Either way, any layer of rock that covered these areas since then has been eroded away, either by water or wind.
Liu said the samples from Seitah were a coarse-grained igneous rock containing the mineral olivine, noting that three Martian meteorites found on Earth have similar composition.
Examining samples on Earth could reveal when the rock was formed and give a firmer answer as to when there was water on the Martian surface. Liquid water is a key ingredient of life.
“Understanding when and for how long the climate on Mars allowed the stability of liquid water is of central importance to the larger questions we are trying to address with this mission and the samples taken — about whether and when life may have existed on Mars billions of years ago. ago,” said geochemist and study co-author David Shuster of the University of California at Berkeley.
Translated by Luiz Roberto M. Gonçalves
