If Viking was phase one of our search for life on Mars, and the methodical quest for clues of habitability that followed was phase two, says Grinspoon, "this is the successful culmination of phase two". That leaves open the possibility that microorganisms once populated the red planet - and still might.
But the SAM results were hard to interpret - there were a lot of extraneous signals that didn't make any sense.
Still, "we're in a really good position to move forward looking for signs of life", NASA biogeochemist Jennifer Eigenbrode said in a study published Thursday in the peer-reviewed journal Science. After all, these are just organic molecules on their own, so we're still in the stage of chemistry, rather than biology.
Jen Eigenbrode, a research scientist at Goddard, revealed the first news behind all the hype was the discovery of organic molecules from an ancient lake bed. The researchers suspect the thiophenes' carbon came from as-yet-unidentified larger organic molecules, which had been trapped and preserved inside the jarosite for perhaps billions of years.
At this point, we simply don't know whether the origin is biological or geological. The 96-mile crater, named for Australian astronomer Walter F. Gale, was most likely formed by meteor impact between 3.5 to 3.8 billion years ago. "If you can do this on Mars, imagine what you can do with analytical facilities available to us on Earth", he says. But they aren't proof of life on Mars, or even necessarily strong evidence that there's anything living, or anything that used to be alive, out there.
She isn't ruling out that possibility, however.
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Scientists agree more powerful spacecraft - and, ideally, rocks returned to Earth from Mars - are needed to prove whether tiny organisms like bacteria ever existed on the red planet. The organic compounds aren't even the first molecules of their kind found on Mars, though they are the oldest.
The scientists were surprised to find organic compounds, especially in the amounts detected, considering the harsh conditions, including bombardment of solar radiation on the Martian surface. There may be more material buried deeper. If extraordinary claims require extraordinary evidence, that bar has most certainly not been met here.
The Curiosity rover discovered organic matter preserved in 3-billion-year-old mudstones at the Gale Crater.
Methane is considered the simplest organic molecule.
"The chances of being able to find signs of ancient life with future missions, if life ever was present, just went up", said Curiosity's project scientist, Ashwin Vasavada of NASA's Jet Propulsion Laboratory in Pasadena, California.
Even though the TGO mission can't get as close to the source as the Curiosity Rover, Dr Webster said it could locate potential areas where methane is concentrated or coming from.
"It's coming from sub-surface reservoirs" and then seeping up to the surface, Webster says. For present life, some scientists say we should look below the surface, in soils or in caves, where there might be liquid water still flowing and organic compounds around. Tellingly, the methane levels appear to periodically spike in time with Martian seasons, being about three times higher in the sunny summertime than in the darker, colder winter.