A fresh new look at a 4 billion-year-old Martian meteorite has revealed organic compounds containing nitrogen - the first real evidence of fixed nitrogen molecules on the Red Planet.
Nitrogen is essential for all known forms of life, and while there's currently no evidence to suggest this discovery was created by some biological unit, it does leave open the possibility that once upon a time, Mars might have been a wet and organic-rich planet - a blue planet even - the perfect place for life to begin.
"Early in the Solar System's history, Mars was likely showered with significant amounts of organic matter, for example from carbon-rich meteorites, comets and dust particles," chemist Atsuko Kobayashi from the Tokyo Institute of Technology explains.
"Some of them may have dissolved in the brine and been trapped inside the carbonates."
It's hard to say how these nitrogen-bearing organics may have arisen, but regardless of the explanation, the results suggest Mars may have once been more Earth-like and hospitable to life than it is now - and could have once had its own nitrogen cycle.
"Whatever the origin, the presence of the organic and reduced nitrogen on early/middle Noachian Mars indicates the importance of Martian nitrogen cycle," the authors write.
The meteorite in question was blasted off Mars roughly 16 million years ago, probably by a meteorite impact, and has since survived unfathomable lengths of time and space.
Named ALH84001, it was found in Antarctica's Allan Hills in 1984 and has already become quite famous in the science world. It contains orange-coloured carbonate materials, which seem to have come from some sort of salty liquid on Mars, roughly 4 billion years ago.
Over the years, some scientists have claimed to find bacteria-like microbial fossils in this rock, but there are other non-biological explanations that could also account for their presence.
Martian meteorites are some of the best clues we have about the Red Planet's history, but since these rocks have landed on Earth, it's hard to say how much of them is still truly Martian.
Terrestrial contamination has been a serious problem in the past, but now, using new techniques and state of the art technology, researchers are confident the detected nitrogen-containing organics are "most likely of Martian origin".
Samples of nearby igneous rocks showed no detectable nitrogen, which suggests these organic molecules were only in the meteorite's carbonate.
Trapped here for 4 billion years and preserved across space, the discovery just goes to show how long possible evidence for life can sometimes survive given the right opportunities.
While NASA's Curiosity Rover has detected a form of nitrogen on Mars itself, as well as several other organic compounds, it's hard to conduct and verify all this technical work from so far away. On Earth, we can be much more careful, ensuring that we are testing the right spots with the right methods.
"Several carbonate grains were peeled off from a rock fragment of ALH 84001, using silver double-sided sticky tape, which allowed us to investigate the interiors of the individual carbonate grains," the authors explain.
Obviously, this careful handling isn't something the Mars Rover is up to doing. So meteorites like ALH84001 could provide us with an alternative, allowing scientists to further investigate the history of this planet and its potential to hold life, without actually having to go there.
The study was published in Nature Communications.