NASA celebrated the first anniversary of the Spirit rover's landing on Mars on Monday with a birthday candle that wouldn't go out — an apt symbol for an interplanetary mission that already has lasted four times as long as scheduled.
Exactly one year after Spirit's airbag-cushioned touchdown in Mars' Gusev Crater, mission team leaders looked back at the close calls that almost doomed the six-wheeled, golfcart-sized robot, and looked ahead to new scientific surprises.
The day's most celebrated surprise, however, was the fact that Spirit and its twin robot Opportunity, which landed last Jan. 24, were still in fine working order on Mars.
"Little did we know a year ago that we'd be celebrating a year of roving on Mars," Charles Elachi, the director of NASA's Jet Propulsion Laboratory, said during Monday's ceremonies at the lab in Pasadena, Calif. "The success of both rovers is tribute to hundreds of talented men and women who have put their knowledge and labor into this team effort."
Elachi invited NASA Administrator Sean O'Keefe to blow out the candle on the rover's "birthday cake" — but it turned out that the candle was a party gag, engineered to relight itself whenever it was extinguished.
"The rovers absolutely refuse to go away, so we are going to have the candle lit for the whole year," Elachi said as O'Keefe chuckled at the practical joke.
O'Keefe, who is due to leave the space agency later this year, noted that the Mars missions provided the best evidence yet that planet once had a climate that could have sustained life, with saltwater seas that disappeared long ago under circumstances not yet fully understood.
"The climate, the atmosphere of our closest neighbor was once dramatically different and perhaps conducive to life," O'Keefe said. "Understanding why that changed may provide a whole new perspective of our own place in the solar system, in this galaxy and indeed in the broader universe."
Cornell University astronomer Steve Squyres, the missions' principal scientific investigator, said it would be up to future Mars probes to figure out whether life actually arose on Mars, and whether some form of life might still exist, perhaps deep underground.
"We've set the future Mars program a direction and a goal to pursue," Squyres said.
Billions and billions of bits
Project manager Jim Erickson recapped the mission's statistics so far: Spirit has traveled 2.5 miles (4 kilometers). Opportunity has gone 1.2 miles (2 kilometers). The rovers have transmitted 62,000 images as well as 86 billion bits of additional data.
And the adventure continues: Erickson said the rovers are still "in great shape for their age," although he cautioned that "bad things could happen to us at any time."
Over the course of the past year, mission managers found their way around a potentially fatal memory-management problem that temporarily knocked Spirit out of commission, as well as less serious glitches that affected both rovers (a balky wheel on Spirit, a stuck heater on Opportunity).
The solar panels are still in good shape, and the winter nights turned out to be not quite as cold as expected, which helped the rovers conserve power.
Spirit's scientific surprise
The scientific surprises continue as well: Just in the past few days, Spirit has come across "completely different geological material" in a rock called Wishstone, Squyres said. A chemical analysis of the brushed-off rock determined that Wishstone had a surprisingly high phosphorus content. Squyres speculated that the rock might have been formed in a violent event such as a volcanic eruption or meteor impact, with phosphates deposited by water percolating through the rock.
"These are very, very different sorts of rock than what we found at Opportunity," Squyres said.
Squyres said Spirit would look for additional intriguing rocks in the mountainous area it is now exploring. "Some ways of making phosphates involve water, others do not," he explained. "We want to look at more of these rocks to see if we can distinguish between those possible histories."
Spirit would then would be sent to a lookout point to survey its surroundings for bedrock. Such bedrock outcrops provide the best setting for piecing together the area's geological history — just as they did for Opportunity at the very beginning of its mission.
Opportunity heading south
Opportunity is currently studying the remains of its own heat shield, which hit the Martian surface separately from the rover's lander almost a year ago. "With luck, our observations may help to improve our ability to deliver future vehicles to the surface of other planets," Erickson said.
After analyzing the heat shield's fragments, Opportunity will head south to look at what appears to be a "strangely eroded impact crater" called Vostok, Squyres said, then roll further southward to an area of etched terrain that could provide further insights into Mars' geology.
Every day of extra exploration makes the rover missions, which cost $820 million for the initial 90 days, a better bargain for NASA. Firouz Naderi, head of the Mars Exploration Program at JPL, indicated that the missions would likely be extended as long as the machines were still in working order, at a monthly cost of $3 million. "We will manage somehow," he said half-jokingly.
However, the rovers will eventually fall prey to old age and the elements, just as the less capable Pathfinder rover did back in 1997. Squyres acknowledged that it's only a matter of time before the candles are snuffed out for Spirit and Opportunity as well.
"They will have died honorable deaths when it does happen," he said Monday. "It will be sad, but it will be in its own way satisfying."