Mars may be a parched and inhospitable place today, but recently gathered evidence is gradually painting a portrait of a watery world in its younger years, complete with enduring lakes, oceans and winding rivers. Some of these bodies of water could have lingered for millions of years, perhaps even long enough for life to have had a chance to evolve. But that’s not the only reason that scientists are led to believe that the Red Planet could have once been habitable.
After digging around in Martian soil, NASA’s Curiosity rover found evidence of useful nitrogen compounds that are a vital source of this element for life on Earth. Although we still don’t know whether primitive life forms evolved on ancient Mars, which could have potentially used this form of nitrogen, the data adds to the growing body of evidence that the planet may have once harbored habitable environments that could have sustained life. The study has been published in Proceedings of the National Academy of Sciences.
When we think of the crucial ingredients for life, liquid water and carbon probably first spring to mind, but nitrogen is also a critical element. It’s a major component of the photosynthetic pigment chlorophyll and amino acids, the building blocks of proteins. It’s also found in other important biomolecules like DNA and ATP, the major energy currency of the cell.
Although vital to life, nitrogen needs to be in the right form to be useful. Atmospheric nitrogen typically consists of two atoms tightly bound by a triple bond, which is difficult to break apart and therefore inaccessible. So before it can be utilized by certain life forms, it needs to be broken down and “fixed” into more useful, reactive compounds, such as nitrate (one nitrogen atom bound to three oxygen atoms). On Earth, this process is carried out by specialist nitrogen-fixing bacteria, but lightning also does the job.
Interestingly, it turns out that this process of nitrogen fixation may have occurred on Mars as scientists have now gathered indirect evidence for the presence of nitrate in Martian rocks. Using NASA’s Curiosity rover, samples were collected from three different spots near the probe’s landing site, two of which previously yielded various chemicals and water-modified minerals that indicated the former presence of a potentially habitable body of water, LA Times reports.
The probe then cooked up the samples in its onboard lab and analyzed the gases released. Among those identified, scientists found a significant amount of nitric oxide, which the team believes could have originated from nitrates in the soil since these compounds break down in a predictable way when heated. After taking contamination into consideration, the researchers found concentrations ranging from 70 to 1,100 parts per million of nitrate, which are comparable to the amount found in barren areas of Earth, like the Atacama Desert.
Although the majority of nitrates on Earth are produced by living organisms, such as microbes, finding them on Mars is not necessarily indicative of life. A more likely scenario is that they were produced by some kind of “thermal shock,” such as lightning or impacts from space debris. The researchers therefore plan to continue this work by investigating the potential processes that could have generated these nitrates, and whether they are still at play today.
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