The Curiosity rover has answered a key question about Mars: The red planet in the past had some of the right ingredients needed to support primitive life.

The evidence comes from a chemical analysis by Curiosity, which last month flexed its robotic arm to drill into a fine-grained, veiny rock and then test the powder.

Curiosity is the first spacecraft sent to Mars that could collect a sample from deep inside a rock, and scientists report that they hit pay dirt with that first rock.

"We have found a habitable environment that is so benign and supportive of life that probably if this water was around and you had been on the planet, you would have been able to drink it," said chief scientist John Grotzinger of the California Institute of Technology.

The rover made a dramatic "seven-minutes-of-terror" landing last August near the planet's equator. A key task: Find out if ancient Mars ever had conditions favourable for microscopic organisms.

The car-size rover is not equipped to detect microbes, living or extinct. It can only use its on-board laboratories to examine Martian rocks to determine the kind of environment they might have lived in.

The analysis showed the rock contained clay minerals that formed in a watery environment. It also had traces of sulphur, nitrogen, hydrogen, oxygen, phosphorus and simple carbon — essential chemical ingredients for life.

Unlike some places on Mars, scientists said the ancient water at the site appeared to be neutral and not too salty.

Curiosity previously found a hint of the site's watery past — an old stream-bed that the six-wheel rover crossed to get to the flat bedrock.

Curiosity has yet to turn up evidence of complex carbon compounds, considered life's chemical building blocks. Scientists said a priority was to search for a place where organics might be preserved.

The drilled rock isn't far from Curiosity's landing spot in Gale Crater; the rover is ultimately headed to a mountain in the crater's middle. Images from space spied signs of clay layers at the base of the mountain.

It has been slow going as engineers learn to handle the rover, which is far more tech-savvy than anything that has landed before on the red planet.

Over the years, Mars spacecraft in orbit and on the surface have beamed back a wealth of information about the planet's geology. They've also been able to study rocks from Mars that have occasionally landed on Earth.

Several places on Mars - now a frigid desert - have shown evidence of a warmer and wetter environment early in the planet's history though not necessarily friendly for life.

Scientists said they still intend to drive Curiosity to the mountain, but not until it drills into another rock at its current location.

Since flight controllers on Earth will be out of touch with Mars spacecraft for most of next month due to a planetary alignment, the second drilling won't get under way until May.

In the meantime, engineers are troubleshooting a computer problem on Curiosity, which has not been able to perform science experiments for days.

- AP