A 4 billion-year-old meteorite from Mars that caused a splash here on Earth
decades ago contains no evidence of ancient, primitive Martian life after
all, scientists reported Thursday.
In 1996, a NASA-led team announced that organic compounds in the rock
appeared to have been left by living creatures. Other scientists were
skeptical and researchers chipped away at that premise over the decades,
most recently by a team led by the Carnegie Institution for Science's Andrew
Steele.
Tiny samples from the meteorite show the carbon-rich compounds are actually
the result of water—most likely salty, or briny, water—flowing over the rock
for a prolonged period, Steele said. The findings appear in the journal
Science.
During Mars' wet and early past, at least two impacts occurred near the
rock, heating the planet's surrounding surface, before a third impact
bounced it off the red planet and into space millions of years ago. The
4-pound (2-kilogram) rock was found in Antarctica in 1984.
Groundwater moving through the cracks in the rock, while it was still on
Mars, formed the tiny globs of carbon that are present, according to the
researchers. The same thing can happen on Earth and could help explain the
presence of methane in Mars' atmosphere, they said.
But two scientists who took part in the original study took issue with these
latest findings, calling them "disappointing." In a shared email, they said
they stand by their 1996 observations.
"While the data presented incrementally adds to our knowledge of (the
meteorite), the interpretation is hardly novel, nor is it supported by the
research," wrote Kathie Thomas-Keprta and Simon Clemett, astromaterial
researchers at NASA's Johnson Space Center in Houston.
"Unsupported speculation does nothing to resolve the conundrum surrounding
the origin of organic matter" in the meteorite, they added.
According to Steele, advances in technology made his team's new findings
possible.
He commended the measurements by the original researchers and noted that
their life-claiming hypothesis "was a reasonable interpretation" at the
time. He said he and his team—which includes NASA, German and British
scientists—took care to present their results "for what they are, which is a
very exciting discovery about Mars and not a study to disprove" the original
premise.
This finding "is huge for our understanding of how life started on this
planet and helps refine the techniques we need to find life elsewhere on
Mars, or Enceladus and Europa," Steele said in an email, referring to Saturn
and Jupiter's moons with subsurface oceans.
The only way to prove whether Mars ever had or still has microbial life,
according to Steele, is to bring samples to Earth for analysis. NASA's
Perseverance Mars rover already has collected six samples for return to
Earth in a decade or so; three dozen samples are desired.
Millions of years after drifting through space, the meteorite landed on an
icefield in Antarctica thousands of years ago. The small gray-green fragment
got its name—Allan Hills 84001—from the hills where it was found.
Reference:
A. Steele, Organic synthesis associated with serpentinization and mineral
carbonation on early Mars, Science (2022).
DOI: 10.1126/science.abg7905
Tags:
Space & Astrophysics