NASA's Mars rover has swallowed its first scoopful of dirt from the Red Planet's surface -- and found some bright-colored objects that experts briefly thought might be man-made, the US space agency said Thursday.

In an update on Curiosity's two-and-a-half month old mission, NASA said its Chemistry and Mineralogy (CheMin) instrument, deep in the car-sized rover's belly, will analyze the soil to learn more about its make-up.

Some experts wondered if one of the bright-colored objects -- seen on a photo of a scoop hole in the Martian soil -- could be man-made, like an object seen earlier this month thought to be plastic from the rover itself.

"We began to see some bright flecks in the scoop areas," Curiosity's project scientist told reporters in Pasadena, California, adding: "The science team started calling them schmutz."

Some suggested they could be man-made, but following discussions between scientists and engineers, there was a "strong consensus" that they were indigenous to Mars.

This conclusion was backed by the fact that the objects were left visible at the bottom of holes left by the rover's scoop, meaning they were normally underneath the planet's surface.

"We can't rule out that they're something man-made but we don't think that they are," he said.

Last week, NASA determined that a bright object observed on the ground near the robot several days previously was a bit of plastic that may have dropped from the rover itself, and did not jeopardize the rover's operations.

"The rover team's assessment is that the bright object is something from the rover, not Martian material," the mission said at the time. "It appears to be a shred of plastic material, likely benign."

But for the scientists, the first use of the CheMin device, to analyze the mineral make-up of the Red Planet's soil -- is a major milestone.

"We are crossing a significant threshold for this mission by using CheMin on its first sample," said Curiosity's project scientist, John Grotzinger of the California Institute of Technology in Pasadena.

"This instrument gives us a more definitive mineral-identifying method than ever before used on Mars: X-ray diffraction. Confidently identifying minerals is important because minerals record the environmental conditions under which they form."

Curiosity is on a two-year, $2.5 billion mission to investigate whether it is possible to live on Mars and to learn whether conditions there might have been able to support life in the past.