NASA's Curiosity rover has found nitrogen on Mars in a useable form for the first time.
A team using the Sample Analysis at Mars (SAM) instrument suite has detected nitric oxide that was formed from the breakdown of nitrates in Martian sediment samples during heating.
Nitrogen is an essential ingredient for all known forms of life, as it helps to form the building blocks of DNA and RNA molecules.
However on Mars, as on Earth, the overwhelming majority of atmospheric nitrogen is bound up in molecules of nitrogen gas (N2), and the two nitrogen atoms that make up a molecule of N2cannot easily be separated, or 'fixed'.
On Earth, certain organisms fix atmospheric nitrogen, making metabolic processes possible, but there is no evidence that the fixed nitrogen on Mars came from a biological source.
Instead, what Curiosity found were nitrate (NO3) molecules contained in rock samples.
Nitrate molecules consist of one nitrogen atom bound to three oxgyen atoms, and can react with other molecules.
Soil and mudstone samples from three different sites on the Red Planet were heated, and the gases they gave off were analysed by the SAM team using two instruments: a mass spectrometer and a gas chromograph.
This revealed the presence of nitric oxide (NO).
"Scientists have long thought that nitrates would be produced on Mars from the energy released in meteorite impacts," says Jennifer Stern from NASA's Goddard Space Flight Center, "and the amounts we found agree well with estimates from this process."
The discovery is important because other evidence has already suggested that Mars was once a more hospitable environment, with other elements that are essential to life - liquid water and organic matter - having been present in the Gale Crater region billions of years ago.
So "finding a biochemically accessible form of nitrogen is more support for the ancient Martian environment at Gale Crater being habitable," says Stern.
