San Francisco NASA's Mars rover Curiosity has found organic chemicals the carbon-containing building blocks of life on the Red Planet.

The discovery is not evidence that life exists, or has ever existed, onMars, researchers stressed. But it does mark the first time that organics have been confirmed inside Red Planet rocks, and it checks off a chief goal of the rover team.

"This is really a great moment for the mission," Curiosity project scientist John Grotzinger, of the California Institute of Technology in Pasadena, said during a news conference Tuesday (Dec. 16) here at the annual fall meeting of the American Geophysical Union (AGU). [The Search for Life on Mars in Photos]

The rover's Sample Analysis at Mars instrument (SAM) detected chlorobenzene and several other chlorine-containing carbon compounds in samples from a rock called "Cumberland," which Curiosity drilled into in May 2013.

SAM uses a tiny oven to cook samples, and then analyzes the gases that waft off. Martian soil and rocks commonly host a chlorine-containing chemical called perchlorate, which can destroy or alter organics during this heating process a fact that has complicated Curiosity's hunt for life's building blocks.

In late 2012, for example, mission scientists announced that SAM hadspotted simple chlorinated organicsin samples taken from a different site, called "Rocknest." But they have since determined that this earlier detection probably picked up carbon carried to Mars within SAM.

That's not the case with the more complex chlorobenzene, dichloroethane, dichloropropane and dichlorobutane discovered inside the Cumberland sample, researchers said.

"This is the first in situ detection of organics that are from Mars samples," Caroline Freissinet, of NASA's Goddard Space Flight Center in Greenbelt, Maryland, told Space.com. Freissinet is lead author of the paper detailing the Cumberland results, which has been submitted to the Journal of Geophysical Research.

The apparent ubiquity of perchlorate on Mars makes it tough to know if the original Cumberland sample contained chlorobenzene and the other chlorinated compounds, or some other types of organics. Freissinet, however, is leaning toward the latter explanation.

"Everything is Martian the chlorine and the carbon but it's from two different molecules, and it mixed together in the SAM oven," she said.

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Life on Mars? NASA rover spots ingredients.