After already finding evidence of water on Mars, NASA's Curiosity rover has discovered another key element necessary for life on the Red Planet.
NASA said Tuesday that the robotic rover has, for the first time, detected nitrogen on the Martian surface. The nitrogen -- found in the form of nitric oxide -- could be released during the natural breakdown of nitrates, which are molecules that contain the type of nitrogen that can be used by living organisms.
The discovery does not mean there is life on Mars.
NASA scientists don't believe the nitrogen discovered was created by life on Mars. The nitrogen is likely ancient and could have been deposited there by meteorite impacts and lightning.
The discovery provides scientists with another piece of the puzzle suggesting that ancient Mars once was capable of supporting life.
The detection of nitrogen is a milestone for Curiosity, which was sent to Mars for the sole purpose of finding out if the planet was ever capable of supporting life, even in microbial form.
"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, in a statement. "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."
Evidence has begun to pile up about Mars holding key elements, such as oxygen, nitrogen and hydrogen, needed to support life as we know it on Earth.
Soon after landing on the Martian surface in August 2012, Curiosity discovered evidence that there had been ancient water flows on the planet's surface. Scientists suspect that there was once a steady stream of water running about knee deep.
Curiosity, after drilling into Martian rocks, discovered other elements needed for life -- carbon, hydrogen, oxygen, phosphorus and sulfur.
In December, Curiosity detected a spike in methane, another potential sign of life since it can be produced by bacteria or microbes. Scientists reported at the time that if there's methane on Mars, there could have been -- or could be -- life there.
Now the discovery of nitrogen can be added to the list.
According to NASA, nitrogen is critical for life on Earth. It's used in the building blocks of larger and critical molecules, like DNA and RNA, which hold the genetic instructions for life.