The latest data shows huge swings in the level of methane in the atmosphere as the seasons change, and new types of organic molecules capable of preserving life just beneath its surface. What they found are organic molecules but not something in a molecular form that is important for life.
Organic molecules contain carbon and hydrogen, and also may include oxygen, nitrogen and other elements.
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. Now, samples taken from two different drill sites on an ancient lakebed have yielded complex organic macromolecules that look strikingly similar to kerogen, the goopy fossilized building blocks of oil and gas on Earth. The organic molecules and volatiles, comparable to samples of sedimentary rock rich in organics on Earth, included thiopene, methylthiophenes methanethiol and dimethylsulfide.
"There's a new mission in the planning where they'll be able to drill much deeper than the Curiosity rover can", Freeman says.
Regardless, the detection is a technical achievement, said Williford, because it demonstrates that organic molecules can persist near Mars's surface for billions of years. "And then we went, 'oops, not only did we not find it, but we don't really know what we're looking for if it's not exactly like Earth.' And maybe that was not the best way to go about it".
Curiosity has also found increasing evidence for seasonal variation of methane on Mars - indicating the source of the gas is likely the planet itself, or possibly its subsurface water. Its two-year mission will explore Mars to see if it's "geologically alive", or active below the surface. At a few dozen parts per million, the detected levels are 100 times higher than previous finds, but scientists still can not say whether they have origins in biology or geology.
The surface of Mars may be inhospitable today, but there is strong evidence that the Martian climate once accommodated liquid water - which, as most of you will know, is one of the key components to life - to pool at the surface.
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Ms Campbell said if life did produce the organic molecules it was on the "simpler end of the scale". They could even have been transported from elsewhere in the solar system.
"[Curiosity's] molecular observations do not clearly reveal the source of the organic matter in [Gale Crater]".
However, so far, tests were unable to determine how the organic compounds were formed.
While it could be produced by microorganisms under the surface of Mars, it could also be produced by non-biological processes such as chemical reactions in rocks, or the breakdown of organic matter in dust delivered by comets or meteors, by UV radiation.
NASA will use both these discoveries to inform the design of its upcoming Mars 2020 rover.
The two studies build on and advance smaller detections of atmospheric methane and ancient organic compounds on Mars. "We can find organic matter preserved in mudstones that are more than three billion years old", Siebach said. "But it doesn't tell us that life was there". Eigenbrode says the analyzed rocks came from the bottom of what was once a lake at a time when Mars was a much warmer, wetter place.