The space agency announced Thursday that its Curiosity rover had uncovered "tough" organic molecules preserved in three-billion-year-old rocks in the planet's Gale Crater, which is believed to have once contained a shallow lake.
The molecules contain carbon and hydrogen (two of the so-called building blocks of life) and could potentially include oxygen, nitrogen and other elements, leaving open the possibility that microorganisms once populated our planetary neighbor and might still exist there.
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Though those molecules are commonly associated with organic life, NASA conceded that they could have been produced through other means.
In addition to the organic molecules, NASA also identified seasonal variations in the amount of methane in Mars' atmosphere.
While water-rock chemistry might have produced those variations, NASA said it "cannot rule out the possibility of biological origins." Most of Earth's atmospheric methane comes from animal and plant life and the environment itself.
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Both the atmospheric methane and the preserved carbon have inspired confidence that NASA's forthcoming Mars 2020 rover and the European Space Agency's ExoMars rover could uncover additional evidence for ancient life on the Red Planet.
"With these new findings, Mars is telling us to stay the course and keep searching for evidence of life," Thomas Zurbuchen, associate administrator for the Science Mission Directorate, said in a news release. "I'm confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet."
The Associated Press contributed to this report.