In another hopeful sign that Mars was once habitable, NASA's Curiosity rover has detected nitrogen in the soil of the Red Planet for the first time.

NASA says that the nitrogen was detected indirectly in the form of nitric oxide when soil samples were heated using the mass spectrometer and gas chromatograph on Curiosity's Sample Analysis at Mars (SAM) instrument.

The instruments detected various nitrogen compounds, including nitric oxide, which is produced by the breakdown of nitrates, in amounts that indicate that nitrates were a much more probable source than alternatives.

Nitrates (NO3) are nitrogen-bearing molecules containing nitrogen and oxygen that are basic to biology and are found in DNA, proteins, and many other organic molecules.

On Earth, nitrogen is mostly found in the form of nitrogen gas in the atmosphere, but plants and bacteria are able to "fix" the nitrogen molecules into nitrates, so they can be used by other organisms. However, they can also be produced by lightning or, in the case of Mars, carried down by meteorites.

The nitrates were found in samples of windblown sand and dust collected by Curiosity at the Rocknest site, as well as drill samples from mudstone deposits at Yellowknife Bay. This diversity of samples lead NASA to the conclusion that the nitrates are widespread on Mars with concentrations of 1,100 parts per million at the drill sites.

NASA doesn't think that Martian nitrates are biological in origin, but they are still significant because the survival of such molecules indicate that Mars was once much more favorable to life in the ancient past.

"Scientists have long thought that nitrates would be produced on Mars from the energy released in meteorite impacts, and the amounts we found agree well with estimates from this process," says Jennifer Stern of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The Curiosity findings were published in the Proceedings of the National Academy of Science.

Source: NASA