What has Nasa found on Mars? Alien life? Watch announcement livestream here

On the top of scientists' wish list was evidence of organic matter, which emerged in 2013. The two rock samples, from sites named Confidence Hills and Mojave, are at the bottom of Gale Crater.

And that did the trick.

The new findings are also detailed in two studies published Thursday in the journal Science.

"What we have detected is what we would expect from a sample from an ancient lake environment on Earth", said Eigenbrode, of NASA's Goddard Space Flight Center.

Is this the discovery of Martians? In this case, the scientists couldn't tell how these organics were formed. The organic compounds aren't even the first molecules of their kind found on Mars, though they are the oldest. That doesn't necessarily mean that Curiosity discovered signs of past life. "We now have really good reasons to look a whole lot harder", he says.

Since it landed at the Gale Crater in 2012, the Curiosity Rover has been sniffing out methane in the area.

NASA's Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft effectively ruled out cosmic origins following its analysis of the dust left after a close encounter with the comet Siding Spring in 2014. On Mars, where we only have a few molecules from a remote probe, this stuff is light years away from being conclusive. The innumerable technological advances which space explorations have given us? What do we stand to gain from these missions anyway? Serpentinisation is still on the table, as are minute traces delivered by asteroids, and other chemical processes. However, the abundances of methane measured are greater than models predict should occur, meaning we still don't know exactly how they are produced.

In a second, potentially more significant finding announced Thursday, scientists reported detection of a seasonal variation in methane levels in the martian atmosphere.

Clearly, there are more questions about Mars that need answering. And now they've added a catalogue of organic molecules to that list. This doesn't constitute proof that life existed on Mars, though. Finding organics is critical.

The term "organic" means something different to a chemist than it does to a produce manager at a grocery store.

Scientists have been seeking organic molecules on Mars ever since the 1976 Viking landers. Regardless of how these molecules originated, they are a key sign of habitability.

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.

The team picked up a welter of closely related organic signals reflecting dozens or hundreds of types of small carbon molecules, probably short rings and strands called aromatics and aliphatics, respectively.

"If we weren't sure, we removed it", Dr. Eigenbrode said.

NASA will use both these discoveries to inform the design of its upcoming Mars 2020 rover. The Wikipedia article on "organic matter" makes the point: "Organic molecules can also be made by chemical reactions that don't involve life". And scientists already expected that, in the early, more turbulent days of the solar system, organic compounds would rain down on Mars. That next step is to try to figure out if life is involved.

Although there is not enough information to know whether the carbon molecules were created by biological or non-biological processes, it is possible that they could be a source of methane, Dr Eigenbrode said. "Whether there was in the past or not is certainly an open question". This new discovery of old organics strengthens that possibility and offers new insights into how things preserve in Mars rock, Grinspoon says.

(Copyright © 2015. All Rights Reserved.)

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