Rock-hunting NASA rover reveals Martian crater's surprising geology
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[August 26, 2022]
By Will Dunham
WASHINGTON (Reuters) - Core samples drilled
by NASA's Perseverance rover on the Martian surface are revealing the
geology of a gaping crater scientists suspect may have harbored
microbial life billions of years ago, including surprises about the
nature of the rock present there.
The samples, obtained by the car-sized, six-wheeled robotic rover and
stored for future transport to Earth for further study, showed that rock
from four sites inside Jezero crater is igneous - formed by the cooling
of molten material. The rocks also bore evidence of alteration through
exposure to water, another sign that cold and arid Mars long ago was
warm and wet.
The scientists had thought the rock, formed roughly 3.5 billion years
ago, might be sedimentary, formed as mud and sand deposited in a
lakebed.
"In fact, we found no evidence of sedimentary rocks where the rover
explored the crater floor, despite the fact we know the crater once held
a lake and sediment must have been deposited. Those sedimentary deposits
must have eroded away," said Caltech geochemist Kenneth Farley, lead
author of one of four studies published in the journals Science and
Science Advances describing the crater's geology.
Perseverance arrived on Mars in February 2021 and has been busily
working in Jezero crater since then, using a suite of instruments, as
scientists probe whether Earth's closest planetary neighbor ever
possessed conditions conducive to life.
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It is gathering rock samples, about the size of blackboard chalk, in
small tubes due to be retrieved by a spacecraft in 2033 and brought to
Earth for further examination including for biosignatures - indicators
of life.
Jezero crater is 28 miles (45 km) wide, located just north of the
Martian equator. It appears the area once was abundant with water and
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 lakebed or shoreline
rock.
Perseverance is now collecting samples in the delta area.
The crater's igneous rocks were found to have interacted with water,
making new minerals and depositing salts, though this water apparently
was either in low abundance or not present very long - likely
groundwater. But the water's presence suggests this might have been a
habitable environment at the time, the researchers said.
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![](../images/082622PIX/news_g11.jpg)
Wheel tread marks are left in the soil
of Jezero Crater on Mars, as NASA's Mars rover Perseverance drives
on Martian surface for the first time, in this March 4, 2021 image
supplied to Reuters. Image taken March 4, 2021.
NASA/JPL-Caltech/Handout via REUTERS
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"We collected samples that will be returned to Earth, and they
should provide critical evidence of what kinds of organisms, if any,
inhabited the Jezero crater floor rocks when they were interacting
with water," said Yang Liu, a planetary sample scientist at NASA's
Jet Propulsion Laboratory and lead author of one of the studies.
The four samples were drilled from two areas, one called Seitah and
the other Maaz. The Seitah rock appears to have formed underground
through slow cooling of a thick sheet of magma. The Maaz rocks may
have cooled relatively more quickly in an upper layer of underground
magma or after a volcanic surface eruption. Either way, any rock
layer that once covered these areas has since eroded away, either
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 the samples back on Earth may reveal when the rock was
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, the climate conditions on
Mars allowed for the stability of liquid water is of central
importance to the larger questions that we are attempting to address
with this mission and sample return - on whether and when life could
have once existed on 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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