Life on Mars: Rover begins epic search
The landing procedure began at around 4.30am when the probe successfully rotated its thermal shield forward to protect it from the heat of the Martian atmosphere.
Before taking the plunge, Spirit separated from the cruising stage rocket that had carried it for seven months and over 300 million miles from Earth.
Less than two minutes before landing, the engine opened its parachute and, 20 seconds later, the probe jettisoned the spent lead edge of its heat shield, exposing the rover's protective cone, encased in uninflated air cushions.
Six seconds before hitting the surface, the cushions inflated, and rockets on the upper shell of the shield fired to stabilise the engine. At about 15 metres from the surface, the tether to the parachute was cut.
The robot then fell freely, bouncing a dozen times on the surface before coming to rest half a mile away.
Jubilant scientists and engineers at the Jet Propulsion Laboratory (JPL) in California monitored the craft's tricky list of entry, descent, and landing duties via a series of tones.
The signals relayed from the Mars-bound Spirit helped ground controllers assess the state of the rover as it fell into a pre-selected landing zone within the centre of Gusev Crater, thought to have held a lake long ago.
NASA scientists will spend the next days preparing the Spirit explorer to start moving about Mars, and acquiring additional images of the area where it landed.
They will conduct "health checks" on instruments aboard the vehicle to see if they survived the jolt of landing, said Stephen Squyres, a geologist in charge of Spirit's scientific instruments.
NASA's 650-million dual Mars Exploration Rover project Spirit and the still en route Opportunity are designed to build upon a legacy of earlier discoveries about Mars.
The two specially-equipped robots were hurled toward Mars to gain new insights regarding the history of environments on the planet perhaps hospitable to life in the past or possibly today.
Following touchdown on Mars, each rover has been built to carry out three months of exploration at their respective landing spots.
Both Spirit and Opportunity are geared to wheel across Mars, inspecting their surroundings with a stereo, colour camera and with an infrared instrument that can classify rock types from a distance.
Rocks that are deemed by scientists to be the most interesting can be subjected to a handful of tools attached to a rover's robotic arm.
"The focus of the next nine sols or however long it takes is getting the vehicle ready to explore, but in amongst those activities will be this image acquisition," Mr Squyres said. A sol is a Martian day.
"So what you're going to see over the coming days is a gradual buildup of what will be an absolutely stunning pan-cam panorama of the terrain around this vehicle."
This robot craft is heading for Meridiani Planum, a region on Mars that contains exposed deposits of a mineral gray hematite that usually forms under watery conditions.
Scientists speculate that the hematite might have resulted from environmental conditions indicative of a past lake or active hot springs, perhaps hospitable to life.
The iron oxide mineral could be the result, however, of hot lava, a situation not conducive to supporting life.
"We just got really lucky on this. Everything just broke exactly right. As professional as every one of them is, they never would have dared predict this outcome this early," said NASA administrator Sean O'Keefe, whose family hail from Fermoy, Co Cork.
Sweetening the situation even further, officials said the images showed that the spot where the robot landed was less rocky than expected and therefore an ideal surface for exploring.
"We're seeing a lot of exposed rock but a very good surface for driving. It couldn't be better for what this vehicle was designed for," Mr Squyres said.
Scientists hope that some of those rocks contain sediments that will reveal information about past conditions in the crater, which could be a dry lake bed.
"If we can find sediments and if we can read the story that they have to tell, they can give us a great deal of information about what is was like in this place long ago," Squyres said.
"Was it warm? Was it wet? Was it the kind of place that might have been suitable for life? Our robot detectives are itching to get to work and try to start answering that question," he said.
NASA's triumph comes just days after the planned December 25 arrival of the ill-fated European robot Beagle 2, which has not been heard from since that date.
NASA had cautioned repeatedly about the difficulty of the mission and the risk of failure, noting that of 30 attempted Mars missions over 40 years, just 12 succeeded.
At a record cost of 650 million, the Mars mission will involve 250 NASA specialists and researchers who over three months will micro-manage the six-wheeled rovers, weighing 180 kilograms each, roughly the size of a subcompact car.
In the next days they will be testing instruments aboard the rover and acquiring additional images.
The images seen thus far suggest that the surface around the vehicle is ideal for exploring.
One reason there have been so many losses is that there have been so many attempts.
"Mars is a favourite target," says Dr Firouz Naderi, manager of the Mars Program Office at the Jet Propulsion Laboratory.
The second rover, Opportunity, is zeroing in on its attempted Mars landing on January 24.
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