24 November 2010
Carbonates withstand ultraviolet rays
Some scientists believed that no or few carbonates have been found on the surface of Mars because they had been broken down by UV radiation. The experiment we ran for the first time in space disproves that theory,” affirms Hervé Cottin, as astrochemist at the LISA1 inter-university laboratory for the study of atmospheric systems.
Carbonates are calcareous minerals that only form where liquid water is present.
Some of these minerals are also produced by primitive living organisms like bacteria.
So finding carbonates on the surface of Mars would confirm the presence of liquid water and possibly ancient lifeforms.
Carbonates have been exposed to UV radiation before in the lab but never in real-life conditions. So we placed a few samples of abiotic2 and biotic carbonates inside the BIOPAN module on the Russian FOTON capsule orbiting at an altitude of 300 km,” explains Hervé Cottin.
“After being exposed to solar UV radiation for 12 days, the UVolution experiment was returned to Earth. Analysis of the samples combined with laboratory experiments showed that the carbonates had remained stable,” says Cottin. So there’s no reason why we shouldn’t find carbonates on Mars.
Telltale signs of water and life
Another question intriguing researchers is this: if we do find carbonates on the surface of Mars, could we tell where they came from? In other words, could we find out if they had been produced by bacteria billions of years ago?
“We know that biotic carbonates break down, under certain conditions, at temperatures of around 850°C, whereas abiotic carbonates only break down at 900°C in pyrolysis experiments,” says Fabien Stalport, an astrobiologist at LISA. “And during the UVolution experiment, we showed that carbonates exposed to UV radiation could retain this biological signature."
Hervé Cottin is already looking further ahead: “If we do find carbonates on the surface of Mars—and we are starting to find some locally—all we would need to do, for example, is to heat retrieved samples in an oven to ascertain if they were produced by bacteria.”
Until the day Mars rovers are able to scoop up samples of the precious minerals, a new experiment called PSS3 is set to be performed on the International Space Station in 2012.
And this time, carbonates will be exposed to UV solar radiation for 18 months.
1 Laboratoire Interuniversitaire des Systèmes Atmosphériques (Paris-Est Créteil and Paris Diderot universities, UMR 7583 CNRS, IPSL).
2 Produced by physical-chemical processes rather than biological processes.
3 Photochemistry on the Space Station.