NASA's Curiosity rover found nitrogen on Mars' surface from release during heating of Martian sediments, by using the Sample Analysis at Mars (SAM) instrument.
The nitrogen was detected in the form of nitric oxide, and could be released from the breakdown of nitrates during heating. Nitrates are a class of molecules that contain nitrogen in a form that can be used by living organisms. The discovery adds to the evidence that ancient Mars was habitable for life.
Nitrogen has been essential for all known forms of life, since it's used in the building blocks of larger molecules like DNA and RNA, whichencode the genetic instructions for life, and proteins, which are used to build structures like hair and nails, and to speed up or regulate chemical reactions.
There was no evidence to suggest that the fixed nitrogen molecules found by the team were created by life. The surface of Mars is inhospitable for known forms of life. Instead, the team thinks the nitrates are ancient, and likely came from non-biological processes like meteorite impacts and lightning in Mars' distant past.
Features resembling dry riverbeds and the discovery of minerals that form only in the presence of liquid water suggested that Mars was more hospitable in the remote past. The Curiosity team has found evidence that other ingredients needed for life, such as liquid water and organic matter, were present on Mars at the Curiosity site in Gale Crater billions of years ago.
The team found evidence for nitrates in scooped samples of windblown sand and dust at the "Rocknest" site, and in samples drilled from mudstone at the "John Klein" and "Cumberland" drill sites in Yellowknife Bay.
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Along with other nitrogen compounds, the instruments detected nitric oxide (NO, one atom of nitrogen bound to an oxygen atom) in samples from all three sites. Since nitrate is a nitrogen atom bound to three oxygen atoms, the team thought most of the NO likely came from nitrate which decomposed as the samples were heated for analysis.
Certain compounds in the SAM instrument could also release nitrogen as samples are heated; however, the amount of NO found was more than twice what could be produced by SAM in the most extreme and unrealistic scenario. This led the team to think that nitrates really are present on Mars, and the abundance estimates reported have been adjusted to reflect this potential additional source.
The research is published online in the Proceedings of the National Academy of Science.