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

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New Mars discoveries are advancing the case for possible life on the red planet, past or even present.

Organic matter has been found on Mars in soil samples taken from 3 billion-year-old mudstone in the Gale crater by the Curiosity rover, NASA announced Thursday.

The scientists hope to find better preserved organic compounds with Curiosity or other rovers that would allow them to check for chemical signatures of life.

But Curiosity's data are providing a clearer and more conclusive picture of the conditions and processes on Mars - and what it may have been like on the Red Planet billions of years ago, when conditions were more suitable for life.

Dr Webster is also awaiting results from the current ExoMars Trace Gas Orbiter (TGO) mission, which is orbiting the Red Planet, sniffing methane.

In 2013, it confirmed organic compounds in rocks in a deep part of the crater called Yellowknife Bay, said Jennifer Eigenbrode, who led the organic molecule study published in Science.

On top of that, after keeping close tabs on methane levels in the Martian atmosphere, scientists have finally confirmed something weird is definitely going on, and they think they know what's causing it. Researchers said they can't rule out a biological source. Most of Earth's atmospheric methane comes from animal and plant life, and the environment itself. In a companion article, an outside expert describes the findings as "breakthroughs in astrobiology".

Organic molecules are the basic building blocks of life - and they are also left behind by living organisms.

Kirsten Siebach, a Rice University geologist who also was not involved in the studies, is equally excited. She said the discoveries break down some of the strongest arguments put forward by life-on-Mars skeptics, herself included.

NASA says the announcement has something to do with "new science results from NASA's Curiosity rover", which tells us quite a bit about what the news might be.

"We've been able to rule out some of the more simple or accepted ideas of Mars's methane", Dr Webster said.

"The question of whether life might have originated or existed on Mars is a lot more opportune now that we know that organic molecules were present on its surface at that time".

"The seasonal methane peaks in the summer of the Martian northern hemisphere so the source has to be affected by those increasing temperatures from greater sunlight", astrophysicist Alan Duffy from Swinburne University in Australia told ScienceAlert.

JPL's Christopher Webster, lead author on the study, said it's the first time Martian methane has shown a repeated pattern.

"We've considered three possible sources for the organics: geology, meteorites and biology", she said. "It's tripling. that's a huge, huge difference".

There is a seasonal variation to the methane that repeats, which means the methane is being released from the Martian surface or from reservoirs beneath the surface.

"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.

Scientists have been seeking organic molecules on Mars ever since the 1976 Viking landers.

These molecules appeared to come from a much larger molecule, and contained high levels of sulfur. Curiosity has had a somewhat rough go of things over the past few months, breaking its drilling mechanism and having to totally relearn how to use its tool in a new way so that it can continue to pierce Martian rocks.

Intriguingly, the organics Dr. Eigenbrode and her colleagues detected looked like they were pieces that came from more complex material.

They hit pay dirt about 6.5 kilometres away, at two sites near Pahrump Hills at the base of Mt Sharp.

As with methane, there could well be non-biological explanations for the presence of carbon-containing molecules on Mars, such as geologic processes or impacts by asteroids, comet, meteors and interplanetary dust.