Scientists reported Thursday that a 4 billion-year-old Martian meteorite that caused an outburst here on Earth decades ago contains no evidence of ancient, primitive Martian life.
In 1996, a NASA-led team announced that the organic compounds in the rock appeared to have been left behind by living things. Other scientists were skeptical, and researchers have been dropping this premise for decades, most recently a team led by Andrew Steele at the Carnegie Institution of Science.
Tiny meteorite samples show that the carbon-rich compounds are actually the result of water — most likely salt or salt water — flowing over the rock for an extended period of time, Steele said. The findings are published in the journal Science.
During Mars’s wet and early past, the rock experienced at least two impacts, heating the planet’s surrounding surface, before a third impact threw it off the red planet and into space millions of years ago. A 2-kilogram (4-pound) stone was found in Antarctica in 1984.
Groundwater flowing through cracks in the rock while still on Mars formed tiny globules of carbon, the researchers say. The same could happen on Earth, they said, which could help explain the presence of methane in the Martian atmosphere.
But the two scientists who took part in the original study disagreed with these latest findings, calling them disappointing. In a shared email, they said they stick with their 1996 observations.
“While the data presented gradually add to our knowledge of (the meteorite), the interpretation is unlikely to be new and not supported by research,” write Cathy Thomas-Keprta and Simon Clemett, astromaterials researchers at NASA’s Johnson Space Center in Houston.
“Unverified speculation does nothing to solve the mystery of the origin of organic matter” in the meteorite, they added.
According to Steele, advances in technology have made his team’s new discoveries possible.
He praised the measurements made by the original researchers and noted that their life-affirming hypothesis “was a reasonable interpretation” at the time. He said that he and his team, which includes NASA, German and British scientists, made sure to present their results “as they are, which is a very exciting discovery about Mars, not a study to disprove” the original premise. .
The discovery is “huge for our understanding of how life began on this planet and helps refine the methods we need to search for life elsewhere on Mars, Enceladus and Europa,” Steele said in an email, referring to Saturn’s moons and Jupiter with subsurface oceans. .
According to Steele, the only way to prove that Mars ever had or still has microbial life is by bringing samples back to Earth for analysis. NASA’s Perseverance rover collected six samples to return to Earth in about ten years; three dozen samples are desirable.
Millions of years after drifting through space, a meteorite landed on an ice field in Antarctica thousands of years ago. The small grey-green fragment gets its name – Allan Hills 84001 – from the hills where it was found.