"With these new findings, Mars is telling us to stay the course and keep searching for evidence of life", said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters, in Washington.
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.
"For the first time we have something that we can get a handle on", said Dr Webster of NASA's Jet Propulsion Laboratory.
The rover also found seasonal fluctuations of atmospheric methane.
The methane could simply be the product of basic geological processes, but it's possible the gas has origins in biological sources. Sadly, most scientists dismissed this claim in the decade that followed - finding other explanations for the rock's formation. Together, the researchers believe these findings to be "breakthroughs in astrobiology". The host of the session, assistant director of science for communications in NASA's Planetary Science Division Michelle Thaller, began by clearing up any rumors that the agency would announce that they had found alien life.More news: De Bruyne: Maybe Guardiola thought Toure wasn't fit enough
"The detective work they did is worthy of Sherlock Holmes", said Katherine Freeman, a professor of geosciences at Pennsylvania State University who was not involved with the research.
"The big takeaway is that we can find evidence".
Both the methane gas and soil compounds are organic matter. But scientists revealed tantalizing hints about present-day Mars today, too.
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.
By examining data spanning almost three Martian years (six Earth years), Webster and his colleagues discerned the first repeating pattern in Martian methane. This new result shows that low levels of methane within Gale Crater repeatedly peak in warm, summer months and drop in the winter every year.
"Even nowadays on Earth, we see a large influx of extraterrestrial [organic] material in the form of interplanetary dust and meteorites", ten Kate said. "It's tripling ... that's a huge, huge difference".More news: Facebook has reportedly been sharing user data with phone makers for ages
The samples were drilled from the base of Mount Sharp, inside a basin called Gale Crater. The diameter is slightly smaller than a USA dime.
So, just where did the methane come from in the first place? Once at the surface, the methane sticks to dirt and rocks, with more released into the atmosphere when it's hotter.
"Now we have data to confirm that there's a seasonal cycle, suggesting the methane is being generated by something".
NASA now operates three orbiters and two surface rovers at Mars with a new lander - InSight - on the way.
NASA officials discuss the findings of the Mars Curiosity rover. They could even have been transported from elsewhere in the solar system. The key samples in the latest findings came from a spot 6.4 kilometres away.
The team also found several spikes where methane abundance suddenly jumped to be higher than average during the year.More news: Arjun Tendulkar gets nod for U-19 Lanka tour
"Curiosity has not determined the source of the organic molecules", Jen Eigenbrode of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said.
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