NASA's Curiosity rover has found further evidence that ancient Mars was habitable for life with the first detection of a biologically friendly form of nitrogen on its surface.

The science team used Curiosity’s Sample Analysis at Mars (SAM) instrument suite to detect the release of nitrogen compounds and nitric oxide gas by heating up soil samples taken from various sites. These include "Rocknest," along with "John Klein" and "Cumberland" Yellowknife Bay drill sites in Gale Crater.

The discovery adds to previous evidence that the crater and potential former lake site, Yellowknife Bay, may have hosted an ancient habitable environment containing the building blocks needed for life: fresh water, carbon and energy sources.

Loading

"Finding a biochemically accessible form of nitrogen is more support for the ancient Martian environment at Gale Crater being habitable," said Jennifer Stern of NASA's Goddard Space Flight Center, lead author of a paper published in the Proceedings of the National Academy of Science.

The recent nitric oxide discovery is believed to be result of the breakdown of nitrates during heating, a class of molecules containing a form of nitrogen that can be used by living organisms.

Atmospheric nitrogen have two atoms of nitrogen bound together to make nitrogen gas (N2) an are bounded so strongly it makes it difficult for it to react with other molecules. These nitrogen atoms have to be separated or “fixed” in order to contribute to chemical reactions needed for life. On Earth, atmospheric nitrogen can be fixed by select organisms or charged events like lightning strikes.

Loading

These fixed sources of nitrogen are known as nitrate molecules that can join with various other atoms and molecules. However, the team currently believes that there’s no evidence that the fixed nitrogen molecules they found evidence of were created by biological organisms and may have been the product of meteorite impacts and past lightning strikes.

"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," said Stern.

NASA revealed earlier this month that Curiosity also analysed a network of two-tone mineral veins at an area called "Garden City" on lower Mount Sharp that offer clues about multiple episodes of fluid movement. The team found that these episodes happened after the wet environmental conditions that formed lake-bed deposits the rover examined at the mountain's base in 2012.

Scientists have previously discovered that Mars may once had a massive ocean covering half of its northern hemisphere and evidence of riverbeds through the discovery of minerals that only form in the presence of liquid water.Image Credit: Image Credit: NASA/JPL-Caltech/MSSS

Jenna Pitcher is a freelance journalist writing for IGN. You can follow her on Twitter