The probe transmitted a black-and-white image of its base station after rolling onto the Martian surface at 1100 GMT, nearly a week after landing on the planet, indicating its journey had been a success. The six-wheeled vehicle's tracks could clearly be seen in the image.

Controllers, optimistic about the mission's success, had decided to move the probe 24 hours earlier than planned.

"We're ahead of schedule and taking advantage of the fact that Opportunity treats us well," Daniel Limonadi, rover systems engineer at NASA's Jet Propulsion Laboratory in Pasadena, California, said in a statement.

Opportunity, the second of a pair of US Martian probes, landed on January 24 inside a small crater in an area of Mars known as the Meridiani Planum, believed to be the flattest place on the planet.

The first probe, Spirit, resumed transmitting data Thursday from the opposite side of the planet after more than a week of silence caused by software problems, NASA said.

Scientists involved in the 820-million-dollar research project have said they are impressed by the data already sent and have high hopes for the mission.

Engineers cheered at 1101 GMT, when NASA received confirmation that Opportunity had successfully descended from its platform onto the Martian surface.

A minute later, the black-and-white image of Opportunity arrived. The robot had photographed what it had left behind, the platform and its tracks in the dust.

It took Opportunity seven days to descend from its shipping platform, while Spirit took 12, having to negotiate its way through deflated air bags which had cushioned its descent but hindered its movement.

Spirit, on the opposite side of Mars, began to trek in Gusev crater on January 15, before a computer crash on January 21 interrupted its duties.

On the science side, the first data sent by Opportunity show that it landed in an area high in hematite, an iron oxide typically formed in moist conditions. Scientists selected the site for that reason, since the goal of the mission is to search for indications that Mars may once have had enough water for a sufficient period to sustain life.

Over the coming days, Opportunity will extend its arm to examine the Martian soil up close.

Opportunity carries a Mossbauer spectrometer to determine the composition of rocks. It is the most fragile and most useful of the instruments and will be tested this weekend, along with an alpha particle X-ray spectrometer, which analyzes geological material.

Spirit has been able to send new images it took Thursday with its high-resolution panoramic camera, as well as photographs of two rocks, which mission scientists dubbed Cake and Blanco.

SPACE.WIRE