The Mars rover Opportunity has rolled off its lander on to the surface of the Red Planet, a week after arrival.
The rover's first journey was seen as the hardest
The operation went as planned, a Nasa spokesman said, with the robot coming to a halt a short distance away.
The mission of Opportunity and its twin Spirit is to explore the rocks and soil of their landing sites for evidence of past wet environments.
Spirit is returning to working order after communication problems following its arrival on 4 January.
The rovers are on opposite sides of the planet to each other.
Spirit is sitting in Gusev Crater, which may have once held a lake.
Opportunity landed on Meridiani Planum, a region containing exposed deposits of the mineral haematite, which usually forms under watery conditions.
A single black-and-white image transmitted via satellite back to Earth showed the empty lander behind Opportunity and a parallel set of tracks leading away from it.
Engineers at US space agency's (Nasa) Jet Propulsion Laboratory in Pasadena, California, erupted in cheers as confirmation came through that the six-wheeled robot had successfully moved down its ramp.
An old hit by the UK rock group The Who, Going Mobile, accompanied the news.
"Two for two, one dozen wheels on soil," was how flight director Chris Lewicki put it as Opportunity joined its twin on the planetary surface.
Opportunity will now have a close look at the surrounding soil.
Grey granules covering most of the crater floor contain haematite, said Phil Christensen, lead scientist for both rovers' miniature thermal emission spectrometers (MiniTes), which are infrared-sensing instruments used for identifying rock types from a distance.
Crystalline haematite is of special interest because, on Earth, it usually forms under wet environmental conditions.
The concentration of haematite appears strongest in a layer of dark material above a light-covered outcrop in the wall of the crater where Opportunity sits, Christensen said.
"As we get out of the bowl we're in, I think we'll get on to a surface that is rich in haematite," he added.
Spirit is using its high-gain antenna again to communicate with Earth and the on-board scientific instruments are also being deployed once more.
When the vehicle broke down on 22 January, it was poised to examine a rock nicknamed Adirondack.
Microscopic images were about to be obtained of the surface of the boulder and the Moessbauer spectrometer was going to help identify Adirondack's mineralogy.
Now that examination has been done and the data has been returned to scientists.
The microscopic images indicate Adirondack is a hard, crystalline rock. The
Moessbauer readings reveal the minerals in the rock include olivine, pyroxene and magnetite.
That composition was common in volcanic basalt rocks on Earth, said science team member Dick Morris. Spirit will now grind into Adirondack to inspect its interior.
Engineers still have to get on top of the problems in Spirit's flash memory system.
They plan to delete large numbers of redundant files in the system which, it is hoped, will then allow the vehicle to resume normal computer operations.