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NASA Rover on Mars: “We Need More Evidence to Say We’ve Identified Life”

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NASA’s Curiosity rover makes an unusual find on Mars that would indicate a biological influence on Earth. What’s behind it?

Washington DC – Carbon is a building block of life and is found everywhere on earth. That’s why researchers prick up their ears when a rover on Mars makes discoveries related to carbon. The latest example of this is the NASA rover “Curiosity”, which has been active on the red planet since summer 2012. According to NASA, the rover found particularly large amounts of a carbon isotope in several soil samples that is associated with biological processes on Earth.

The find is “fascinating,” according to NASA. But life on Mars cannot and does not want to be confirmed at the US space agency: Researchers have not yet found “conclusive, supporting evidence for ancient or current biology”. This includes, among other things, sedimentary rock formations that were created with the help of bacteria or complex organic molecules that were formed by living beings. “We’re finding things on Mars that are infuriatingly exciting, but we really need more evidence to say we’ve identified life,” said Paul Mahaffy, who will operate the Curiosity instrument until his retirement in December 2021 “Sample Analysis at Mars” (SAM). SAM is a kind of small chemistry laboratory on board the rover. “We’re trying to figure out what might have caused this carbon signature if it wasn’t life,” Mahaffy said.

NASA’s Curiosity rover makes a “fascinating” find on Mars

A study of Curiosity’s findings was published in the journal Proceedings of the National Academy of Sciences. In it, the researchers describe various explanations for the unusual carbon signals on Mars. The particular difficulty seems to be knowing a lot about carbon on Earth. “The hardest thing is not thinking about Earth,” said astrobiologist Jennifer Eigenbrode in a NASA statement. “We have to think outside the box,” emphasizes the researcher and explains: “That’s what we’re doing in this study.”

NASA’s Curiosity rover on Mars. (archive image)

© Nasa/JPL

One explanation for the carbon discovery on Mars, which the researchers write down, is biological in nature and actually even inspired by life on earth, as NASA says. It’s about ancient bacteria on the surface of Mars that may have produced the unique carbon signature through their metabolism: methane is released into the atmosphere, where ultraviolet light converts the gas into larger, more complex molecules. These molecules could then have rained down onto the surface of Mars and been preserved in rocks on Mars, the theory goes.

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Mars: Carbon isotopes could come from giant molecular cloud

Another – non-biological – theory proposed by the researchers suggests that the carbon on Mars is related to an interaction of carbon dioxide with ultraviolet light in the atmosphere. This could have created new molecules containing carbon, which then settled on the surface of Mars. Another theory holds that the carbon arrived on Mars hundreds of millions of years ago when the solar system passed through a giant molecular cloud rich in the identified species of carbon.

As different as the three attempts at explanation are, they have one thing in common: “All three explanations fit the data,” emphasizes the “Curiosity” scientist Christopher House, who led the study. “We just need more data to include or rule out the explanations.”

NASA’s Curiosity rover analyzed 24 Mars rock samples

The rock samples Curiosity found carbon signatures in come from five different locations in Gale Crater on Mars. A total of 24 samples were heated to 850 degrees Celsius in the SAM instrument, after which another instrument was used to measure the isotopes released by the heating. There are significantly more of the lighter C12 isotopes on Earth than the heavier C13. Now, large amounts of C12 isotopes have been found in almost half of the samples analyzed on Mars – in contrast to what has been measured in the Martian atmosphere or in Martian meteorites so far.

A well drilled by NASA’s Curiosity rover on Mars to collect a soil sample. The carbon isotope C12 was discovered.

© Nasa/JPL

“On Earth, processes that produce this carbon signal are biological,” House explains. “We need to understand whether this explanation also works for Mars or whether there are other explanations because Mars is very different.” While researchers have a good understanding of the carbon cycle on Earth, there is still a lot on Mars that is not known . The planet is smaller and cooler than Earth, has lower gravity, and different gases in its atmosphere. It’s possible that Mars has a carbon cycle that doesn’t involve life at all.

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NASA’s Curiosity rover explores the carbon cycle on Mars

“A large part of the carbon cycle on Earth involves life and because of life there is a part of the carbon cycle on Earth that we can’t understand because everywhere we look there is life,” explains researcher Andrew Steele, who is also involved in the study. “Defining the carbon cycle on Mars is key to understanding how life fits inside,” Steele points out. “We’ve done that very successfully on Earth, but we’re just starting to do it on Mars.” NASA’s Curiosity rover will continue to measure carbon isotopes in future soil sample analysis.

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One of the researchers’ findings could ensure that the second NASA rover “Perseverance” will soon be able to look out for the carbon isotopes: all the soil samples analyzed came from regions that have well-preserved, old surfaces. In the future, “Perseverance” could search for such surfaces in order to take soil samples that could be transported back to Earth in a later Mars mission. Researchers on Earth could then examine the samples from Mars again with other tools – and elicit one or two secrets from the red planet.

Most recently, the NASA rover “Perseverance” caused a stir on the red planet: First it made a “key discovery” on Mars, then “Perseverance” made a sensational find on Mars. (tab)

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