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.
The nuclear-powered rover has detected a variety of organic compounds, a requirement for life as it's known on Earth, in three-billion-year-old rocks deposited on the floor of Gale Crater.
In four locations, including the spot nicknamed Mojave, which Curiosity explored in 2015, the rover discovered thiophenes (molecules that include a ring of carbon and sulphur atoms) and other substances that on Earth can be linked to biological activity.
Organic molecules are considered one of the basic building blocks of life.
"With these new findings, Mars is telling us to stay the course and keep searching for evidence of life", NASA science mission chief Thomas Zurbuchen told USA Today. And if life does exist elsewhere, it may be very different or even form differently from how we understand life on Earth.
Now, the rover has seemingly made a new discovery which will be revealed this Thursday, according to the space agency.
That means they do not have compelling evidence for a biological origin of the carbon, but the possibility is not ruled out, either.
In addition to finding organic molecules in the rocks in Gale Crater, rover scientists are reporting another intriguing finding.
NASA is holding a live conference unveiling the fascinating details it has uncovered Mars from its Curiosity Rover mission.
So NASA astrobiologist Jennifer Eigenbrode at the Goddard Space Flight Center spent the intervening years figuring out which signals were clearly junk and removing them.
Both the methane gas and soil compounds are organic matter.
"The detection of organic molecules and methane on Mars has far-ranging implications in light of potential past life on Mars", said Kate.
SAM measured small organic molecules that came off the mudstone sample - fragments of larger organic molecules that don't vaporize easily.
But Curiosity has discovered "tough" organic molecules from an ancient lake bed inside Gale Crater, showing lakes may have existed for "maybe hundreds or thousands of years".
"That would be exciting because if that is done within two years, NASA can send a mission specifically to that place", he said. But they could also be the result of abiotic chemical reactions on the surface of the planet. This is all written down: the Union Aerospace Corporation went digging around Mars-quite possibly lured in by the discovery of ancient organic material-one thing led to another, and they opened a portal to Hell.
The fact that similar molecules were also present at this new site suggests that this kind of organic material is present in abundance.
The discoveries, reported today in two papers in the journal Science, while not evidence of life, provide more tantalising clues about what's happening on Mars, for future missions to investigate.
The authors of the two studies in Science agree with her, writing that there's no way to tell what produced the molecules And certain features of the molecules show they aren't the direct, unchanged remnants of anything living.
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