A month after it landed on Mars, NASA's Curiosity rover extended its robotic arm this week and began a set of exercises that will test the arm's range of motion before it begins deploying the sampling and drilling tools attached to the complex instrument.

NASA scientists will spend six to 10 days while the rover is parked manipulating the 2.1-metre arm into various positions that it will need to be in when employing its various analytical instruments.

"These activities are important to get a better understanding for how the arm functions after the long cruise to Mars and in the different temperature and gravity of Mars, compared to earlier testing on Earth," Daniel Limonadi, lead systems engineer for Curiosity's surface sampling and science system, said in a media release.

Exercises delayed

The rover was to begin the arm exercises Thursday, but they were aborted after a temperature reading on the arm sent a caution signal; they started Friday instead.

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A new image released by NASA shows the marks left by the rocket-powered descent stage that separated from Curiosity during landing and hit the Mars surface. Possible multiple impacts from that collision are in blue in this enhanced-colour view taken by the camera on the Mars Reconnaissance Orbiter.

The exercises are intended to test out how the arm will scoop up soil, drill into rocks and place samples into its analytical instruments.

"We're still learning how to use the rover," said Joy Crisp, deputy project scientist for the Mars Science Laboratory Project, which built and operates Curiosity from the Jet Propulsion Laboratory in Pasadena, Calif.

"It's such a complex machine — the learning curve is steep."

NASA gave reporters an update on the Curiosity mission on Thursday, saying that since landing inside Mars's Gale crater on Aug. 5 the rover has driven a total of 109 metres, more than the length of a football field. 

The next stop in its two-year stay on the planet will be a rock formation called Glenelg, but it will take the rover several weeks to get there.

Curiosity takes a whiff of Martian air

NASA said the rover has taken its first gulps of Martian air using an instrument called the Sample Analysis at Mars, or SAM, which takes up more than half the payload of science instruments aboard the rover.

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Tracks from the first drives of NASA's Curiosity rover in another image from the Mars Reconnaissance Orbiter. The rover is seen where the tracks end. The image's colour has been enhanced to show the surface details better. (NASA/JPL-Caltech/Univ. of Arizona)

SAM is actually three separate instruments: a mass spectrometer, a gas chromatograph and a tunable laser spectrometer.

These sample and analyze the Martian atmosphere, measuring the abundance of elements such as carbon, hydrogen, oxygen and nitrogen, which will give scientists an indication of whether Mars may have at some point supported microbial life.

Scientists will be looking in particular for signs of methane, a short-lived gas that has been spotted by satellites orbiting Mars and by telescopes on Earth. If present, it will indicate there is some replenishing source of it on Mars.

The air samples Curiosity has begun taking are the first tests of Mars's atmospheric chemistry since the Viking Mars landers explored the planet in the 1970s.

NASA also released new colour pictures of the impact marks left by the rover's descent stage apparatus during landing and tracks the rover made on one of its first drives.

The images were taken by the Mars Reconnaissance Orbiter, which observes Mars from orbit.

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This engineering drawing shows the five devices that make up the turret at the end of the robotic arm on NASA's Curiosity rover. (NASA/JPL-Caltech)