Big news from Mars today: NASA's Curiosity rover found ancient traces of organic matter embedded in Martian rocks and detected a "seasonal variation" in atmospheric methane on the Red Planet - an annual pulse of the gas, nearly as if something out there were breathing.
The case for past habitability on the Red Planet is bolstered by the discovery of preserved organic compounds revealed today, as they are as old as the around 3.5 billion year old sedimentary rocks in which they were found.
What they claimed they had discovered was a fossilised micro-organism in a Martian meteorite, which they argued was evidence that there has once been life on the Red Planet.
Key details about the organics may have been obscured in Curiosity's sample because the rover can only drill two inches into rock.
From everything we can tell of the chemistry and the minerals deposited in the Gale crater where Curiosity is stationed, "we think it was a habitable environment", Jennifer Eigenbrode from the NASA Goddard Space Flight Center told Gizmodo. This doesn't constitute proof that life existed on Mars, though.
Findings from Curiosity also reveal that a water lake inside Mars" Gale Crater once held all the "ingredients necessary for life", including "chemical building blocks and energy sources'. Then the scientists sifted through the results to figure out what might be genuine Martian organics. "If you explore both of those paths forward, it's astounding", Eigenbrode said.
"We were kind of shocked to see that with the seasons, the signal changes by a factor of three, which is a huge change and completely unexpected", says Chris Webster, a rover scientist at NASA's Jet Propulsion Laboratory. That's because the surface of Mars is constantly bombarded with radiation that can break down organic compounds.
These molecules appeared to come from a much larger molecule, and contained high levels of sulfur.
"People have been wondering about whether there might be life on Mars forever and finally ... they've done all the tests they've modified everything to be able to show that in fact there's organic matter on Mars".
"As temperatures change from winter to summer, the methane changes greatly because as the surface gets a little bit warmer it releases a lot more methane", he said.
On Mars, organic molecules could have been produced by some form of either present or past lifeforms.
That means they do not have compelling evidence for a biological origin of the carbon, but the possibility is not ruled out, either. They are fairly certain that it comes from melting water-based crystals, called clathrates, buried just below the planet's surface.
"Are there signs of life on Mars?" asked Michael Meyer, lead scientist for the Mars Exploration Program at NASA Headquarters.
"We have no proof that the methane is formed biologically, but we can not rule it out, even with this new data set", Webster said.
Detecting this organic molecule in the atmosphere, combined with the finding of organic compounds in the soil, has strong implications about potential life on Mars in its past.
"That would be exciting because if that is done within two years, NASA can send a mission specifically to that place", he said.