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NASA's Curiosity finds signs of ancient life on Mars. Or maybe not. More data needed

Rover heats up samples, sniffs carbon signature associated with biological processes on Earth

NASA's Curiosity rover has collected samples of rock from the surface of Mars that are rich in a type of carbon associated with biological processes on Earth.

Is it a sign of ancient life? Well… maybe. It could be the result of methane having been released into the atmosphere of Mars by bacteria. That methane was then maybe converted into "larger, more complex molecules" by ultraviolet light, which rained down to the surface and were preserved (replete with distinctive carbon signature) in the rocks.

At least that's how it works on Earth. The explanation could also be non-biological. It could be down to the interaction of carbon dioxide gas in the atmosphere with ultraviolet light, or perhaps millions of years ago the solar system passed through a giant molecular cloud rich in the type of carbon detected.

As ever, more data is needed and scientists can't make conclusions based on Earth examples.

The findings were published in the Proceedings of the National Academy of Sciences journal yesterday.

Curiosity has rolled around Mars since 2012 covering over 16 miles. On board is the Sample Analysis at Mars (SAM) instrument suite which can analyse organics and gases from atmospheric and solid samples. In this instance, the team used SAM to heat up 24 samples taken from geologically diverse locations in Curiosity's Gale Crater home and heated them to 850°C to release the gases within.

The isotopes were measured using the Tunable Laser Spectrometer (TLS) and, according to the team, "researchers found that nearly half of their samples had surprisingly large amounts of carbon-12 compared to what scientists have measured in the Martian atmosphere and meteorites."

This is significant since, on Earth, processes that would produce this carbon signal tend to be biological. However, the same explanation might not apply to Mars. The planet might have started off with a different set of carbon isotopes than Earth and the carbon might be cycling without any life involved. Again, more data is needed as scientists seek to let go of Earthly biases when looking at Martian processes and chemistry.

Scientists would also really like to check out the carbon content of a methane plume released from the surface. Curiosity happened across one in 2019, but there's no way to know if it will do so again. In the meantime, the study will provide some pointers to the Perseverance rover team on the types of samples to collect for a possible return to Earth. ®

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