This panorama captured by NASA’s Curiosity Mars rover shows a location nicknamed “Pontours” where scientists spotted preserved, ancient mud cracks believed to have formed during long cycles of wet and dry conditions over many years. Such cycles are thought to support conditions in which life could form. Credits: NASA/JPL-Caltech/MSSS/IRAP
A new paper suggests the same
conditions that created the cracks could have been favorable to the emergence
of microscopic life.
Scientists aren’t
entirely sure how life began on Earth, but one prevailing theory posits that
persistent cycles of wet and dry conditions on land helped assemble the complex
chemical building blocks necessary for microbial life. This is why a patchwork
of well-preserved ancient mud cracks found by NASA’s Curiosity Mars rover is so
exciting to the mission’s team.
A new paper in
Nature details how
the distinctive hexagonal pattern of these mud cracks offers the first evidence
of wet-dry cycles occurring on early Mars.
“These particular mud cracks form when
wet-dry conditions occur repeatedly – perhaps seasonally,” said the paper’s
lead author, William Rapin of France’s Institut de Recherche en Astrophysique
et Planétologie.
A close-up of the panorama taken by Curiosity’s Mastcam at “Pontours” reveals hexagonal patterns – outlined in red in the same image, right – that suggest these mud cracks formed after many wet-dry cycles occurring over years. Credits: NASA/JPL-Caltech/MSSS/IRAP
Curiosity is gradually ascending
the sedimentary layers of Mount Sharp, which stands 3 miles (5 kilometers) high
in Gale Crater. The rover spotted the mud cracks in 2021 after drilling a
sample from a rock target nicknamed “Pontours,” found within a transitional
zone between a clay-rich layer and one higher up that is
enriched with salty minerals called sulfates. While clay minerals usually form
in water, sulfates tend to form as water dries up.
The minerals prevalent in each area
reflect different eras in Gale Crater’s history. The transitional zone between
them offers a record of a period when long dry spells became prevalent and the
lakes and rivers that once filled the crater began to recede.
As mud dries out, it shrinks and
fractures into T-shaped junctions – which are what Curiosity discovered
previously at “Old Soaker,” a collection of mud cracks lower
down on Mount Sharp. Those junctions are evidence that Old Soaker’s mud formed
and dried out once, while the recurring exposures to water that created the Pontours
mud caused the T-shaped junctions to soften and become Y-shaped, eventually
forming a hexagonal pattern.
The hexagonal cracks in the
transitional zone kept forming even as new sediment was deposited, indicating
that the wet-dry conditions continued over long periods of time. ChemCam,
Curiosity’s precision laser instrument, confirmed a hardy crust of sulfates
along the cracks’ edges, which isn’t too surprising given the proximity of the
sulfate region. The salty crust is what made the mud cracks resistant to
erosion, preserving them for billions of years.
The Right Conditions
“This is the first tangible
evidence we’ve seen that the ancient climate of Mars had such regular,
Earth-like wet-dry cycles,” Rapin said. “But even more important is that
wet-dry cycles are helpful – maybe even required – for the molecular evolution
that could lead to life.”
Although water is essential to
life, a careful balance is needed – not too much water, not too little. The
kinds of conditions that sustain microbial life – those that allow a
long-lasting lake, for example – aren’t the same as the conditions scientists
think are required to promote chemical reactions that might lead to life. A key
product of those chemical reactions are long chains of carbon-based molecules called
polymers – including nucleic acids, molecules considered to be chemical
buildings blocks of life as we know it.
Wet-dry cycles control the
concentration of chemicals that feed the fundamental reactions leading to the
formation of polymers.
“This paper expands the kind of
discoveries Curiosity has made,” said the mission’s project scientist, Ashwin
Vasavada of NASA’s Jet Propulsion Laboratory in Southern California. “Over 11
years, we’ve found ample evidence that ancient Mars could have supported microbial
life. Now, the mission has found evidence of conditions that may have promoted
the origin of life, too.”
The discovery of the Pontours mud
cracks may in fact have provided scientists their first opportunity to study
the remains of life’s cauldron. Earth’s tectonic plates constantly recycle its
surface, burying examples of its prebiotic history. Mars doesn’t have tectonic
plates, so much older periods of the planet’s history have been preserved.
“It’s pretty lucky of us to have a
planet like Mars nearby that still holds a memory of the natural processes
which may have led to life,” Rapin said.
More About the Mission
Curiosity was built by NASA’s Jet
Propulsion Laboratory, which is managed by Caltech in Pasadena, California. JPL
leads the mission on behalf of NASA’s Science Mission Directorate in
Washington.
For more about Curiosity, visit: http://mars.nasa.gov/msl
Source: Cracks in Ancient Martian Mud Surprise NASA’s Curiosity Rover Team | NASA
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