The finding was made using Curiosity’s Sample Analysis at Mars (SAM) instrumentation suite, part of the complement of scientific instruments carried by the exploration vehicle. By using SAM, Earth based scientists were able to release nitrogen by heating Martian sediment samples.
Nitrogen was detected in the form of nitric oxide (NO) thought to have been released from nitrates contained in the soil samples during heating. The discovery is significant since nitrates are a class of molecules containing nitrogen in a form that can be used by living organisms once again raising the tantalizing prospect that Mars, if not now, then at sometime in the past, harboured conditions suitable for life.
Nitrogen is a vital constituent for all known life-forms. The element is essential for the make-up of larger molecules such as DNA and RNA. These large molecules contain the blueprints that encode the genetic instructions for life as well as proteins. The latter are used to construct adjuncts of life-forms, for example hair, hooves, feathers and nails as well as speeding up or regulating chemical reactions.
But both on Mars and Earth — nitrogen accounts for roughly 80 percent of Earth’s atmosphere — atmospheric nitrogen is locked up as nitrogen gas (N2). So strong are the atomic bonds between the two atoms of nitrogen that go to make up N2 that atmospheric nitrogen doesn’t react readily with other molecules.
These normally ‘locked’ nitrogen atoms must be separated or “fixed” if they are to participate in the chemical reactions needed for life. Some Earth-based life-forms have the ability to fix atmospheric nitrogen, a process critical for metabolic activity. Smaller amounts of nitrogen, however, can also be fixed by high-energy events such as lightning strikes.
Nitrates, found in abundance on Earth, are a source of fixed nitrogen. Nitrates (NO3) comprise one hydrogen atom bound to three oxygen atoms. A nitrate molecule readily combines with other atoms and molecules, an example being potassium nitrate, commonly known as saltpeter.
According to NASA, there’s no evidence suggesting the fixed nitrogen molecules found on Mars were created by life. The inhospitability of present-day Mars hardly makes for an environment conducive for life to exist. Researchers suggest a more likely explanation for the existence of nitrates is that they originate from events in Mars distant past such as meteorite impacts and lightning.
Evidence of nitrates was found in samples of windblown sand and dust scooped up by Curiosity for analysis using the SAM instruments at an area near Gale Crater dubbed “Rocknest” by NASA. Other samples were also drilled from mudstone at the “John Klein” and “Cumberland” sites, two earlier discoveries on Curiosity’s travels.
According to Jennifer Stern, of NASA’s Goddard Space Flight Center, the Rocknest sample comprises dust blown in from other distant areas on Mars as well as local material indicating that nitrates may be widespread on Mars. Sample analysis from the various drill sites indicated the equivalent of up to 1,100 parts per million nitrates in the Martian soil.
Combined with earlier Curiosity discoveries, finding nitrogen is yet another pointer that Mars, if not once home to life, had conditions conducive for life to exist. Earlier, Curiosity has revealed features resembling dry riverbeds while minerals that could only form in the presence of liquid water have been found on the planet. In particular, Curiosity scientists found evidence that some essential ingredients for life, for example liquid water and organic matter, were once present billions of years ago in Gale Crater.
NASA scientists believe that mudstone, not dissimilar to mudflats on Earth, at an area of Gale Crater termed “Yellowknife Bay” formed from sediment deposited at the bottom of a lake. Curiosity scientists had earlier sketched out their vision of an ancient habitable environment in that location: fresh water coupled with key chemical building blocks required by life, such as carbon, and potential energy sources to drive metabolism in simple organisms.
“Finding a biochemically accessible form of nitrogen is more support for the ancient Martian environment at Gale Crater being habitable,” commented Stern who is lead author of a paper on this latest Curiosity research, recently published online in the Proceedings of the National Academy of Science.
“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,” she added.
