NASA's Opportunity rover landed on Mars late on Saturday and sent a signal that it finished its nearly seven-month journey in good condition, engineers at the space agency's Jet Propulsion Laboratory (JPL) said.
At about 9:05pm PST, engineers received a signal that Opportunity had touched down on the Meridiani Planum, a smooth plain near Mars' equator on the other side of the Red Planet from its twin rover, Spirit.
NASA also had good news on Saturday from Spirit, which re-established communications after going quiet on Wednesday.
As Opportunity hit the Martian surface, the JPL control room erupted in cheers as the mission team celebrated the successful conclusion of its 455 million kilometer journey from Earth, and the start of the robotic rover's search for signs of life-giving water.
"We are on Mars, everybody," Wayne Lee, the entry, descent and landing specialist, said after scientists acquired a signal from Opportunity as the spacecraft bounced on the surface.
About 15 minutes after it first signaled its touchdown, Opportunity sent a "no fault" tone indicating that it had arrived in good shape. The pyramid-shaped lander hit the surface with two or three times the force of gravity, bounced, and then sent a signal that it had landed on one of its side.
"We have received tone from Opportunity -- one of the side petals -- the signal is still moving up and down and I am having a hard time believing we are still rolling, frankly," Rob Manning, the entry, descent and landing manager, said.
"Just to remind you, we have no hills where we landed," he added.
Opportunity was designed to land on any of its four sides. The lander was swathed in airbags, and if it did not land on its base, side petals can open in sequence to tip it right side up. In case of a side-petal landing, the opening sequence takes about 35 minutes -- 15 minutes longer than if it had landed on its base petal as did its twin, Spirit.
Opportunity shot through the Martian atmosphere at a rate up to about 20,900kph in what appeared to be a flawless six-minute sequence, exactly like Spirit's landing three weeks earlier.
California Governor Arnold Schwarzenegger and former US vice president Al Gore watched the landing and visited the control room to congratulate the elated scientists immediately after Opportunity made it safely to the surface.
As the spacecraft traveled through the atmosphere it deployed a parachute, jettisoned its heat shield after it absorbed the worst of the searing descent temperatures, and fired retrorockets just above the surface.
The retrorockets had been programmed to stop Opportunity in a hover 12m up. The spacecraft would then drop the last few dozen metres before bouncing to a halt.
NASA engineers also had good news as Spirit re-established contact and began responding to commands. Scientists said it would be back to full operation within weeks.
"I am completely confident, without any hesitation, that I think we will get that rover back to full operation," JPL director Charles Elachi told reporters, estimating several days to a few weeks for the recovery.
Scientists found a possible flaw in Spirit's computer memory and put it in "cripple mode."
That was good enough to upgrade the rover's status from critical to serious.
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