The NASA Rovers on Mars are celebrating five years of service to science this month, outperforming even the best expectations of the team that designed and built them.
Spiritlanded on Mars on 3 January 2004 with
Opportunity arriving on 24 January.
Given that the two vehicles were expected to last for just three months, their longevity in the inclement environment of Mars has been quite a surprise.
NASA's twin robot geologists, the Mars Exploration Rovers, launched toward Mars on 10 June 10 and 7 July 2003, in search of answers about the history of water on Mars. They landed on Mars 3 January and 24 January PST, 2004.
The Mars Exploration Rover mission is part of NASA's Mars Exploration Program, a long-term effort of robotic exploration of the red planet.
Primary among the mission's scientific goals is to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The spacecraft were targeted
to sites on opposite sides of Mars that appear to have been affected by liquid water in the past. Selected were landing sites at Gusev Crater, a possible former lake in a giant impact crater, and Meridiani Planum, where mineral deposits (hematite) suggest Mars had a wet past.
After the airbag-protected landing craft settle onto the surface and opened, the rovers rolled out to take panoramic images. These gave scientists the information they needed to select promising geological targets that tell part of the story of water in Mars' past. Then, the rovers drove to those locations to perform on-site scientific investigations over the course of their planned 90-day prime mission, using a number of instruments to feed information back to Earth including a Panoramic Camera, a Miniature Thermal Emission Spectrometer (for identifying promising rocks and soils for closer examination and for determining the processes that formed Martian rocks), a Microscopic Imager (for obtaining close-up, high-resolution images of rocks and soils) and more.
Before landing, the goal for each rover was to drive up to 40 metres (about 44 yards) in a single day, for a total of up to one kilometre (about three-quarters of a mile). Both goals have been far exceeded!
Moving from place to place, the rovers perform on-site geological investigations, each rover a sort of mechanical equivalent of a geologist walking the surface of Mars. The mast-mounted cameras are mounted 1.5 meters (5 feet) high and provide 360-degree, stereoscopic, humanlike
views of the terrain. The robotic arm is capable of movement in much the same way as a human arm with an elbow and wrist, and can place instruments directly up against rock and soil targets of interest. In the mechanical "fist" of the arm is a microscopic camera that serves the same purpose as a geologist's handheld magnifying lens while their Rock Abrasion Tools serve the purpose of a geologist's rock hammer to expose the insides of rocks.
Above: Full-Circle 'Bonestell' Panorama from Spirit. The view is from the spot where Spirit has spent its third Martian southern-hemisphere winter, on the northern edge of a low plateau informally called "Home Plate." A dotted line marks the edge of Home Plate, which is about 80 meters or 260 feet in diameter.. Image: NASA
At the end of December 2008, NASA issued its own assessment of the five-year mission firm in the belief that both rovers Spirit and Opportunity may still have big achievements ahead as they approached the fifth anniversaries of their memorable landings on Mars.
Of the hundreds of engineers and scientists who cheered at NASA's Jet Propulsion Laboratory in Pasadena, California, on 3rd January 2004, when Spirit landed safely, and 21 days later when Opportunity followed suit, none predicted the team would still be operating both rovers in 2009.
"The American taxpayer was told three months for each rover was the prime mission plan," said Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters in Washington. "The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times."
The rovers have made important discoveries about wet and violent environments on ancient Mars. They also have returned a quarter-million images, driven more than 21 kilometers (13 miles), climbed a mountain, descended into craters, struggled with sand traps and aging hardware, survived dust storms, and relayed more than 36 gigabytes of data via NASA's Mars Odyssey orbiter. To date, the rovers remain operational for new campaigns the team has planned for them.
"These rovers are incredibly resilient considering the extreme environment the hardware experiences every day," said John Callas, JPL project manager for Spirit and Opportunity. "We realize that a major rover component on either vehicle could fail at any time and end a mission with no advance notice, but on the other hand, we could accomplish the equivalent duration of four more prime missions on each rover in the year ahead."
Occasional cleaning of dust from the rovers' solar panels by Martian wind has provided unanticipated aid to the vehicles' longevity. However, it is unreliable aid. Spirit has not had a good cleaning for more than 18 months and dust-coated solar panels barely provided enough power for the rover to survive its third southern-hemisphere winter, which ended in December.
"This last winter was a squeaker for Spirit," Callas said. "We just made it through."
With Spirit's energy rising for spring and summer, the team plans to drive the rover to a pair of destinations about 183 meters (200 yards) south of the site where it spent most of 2008. One is a mound that might yield support for an interpretation that a plateau Spirit has studied since 2006, called Home Plate, is a remnant of a once more-extensive sheet of explosive volcanic material. The other destination is a house-size pit called Goddard.
"Goddard doesn't look like an impact crater," said Steve Squyres of Cornell University, in Ithaca, N.Y. Squyres is principal investigator for the rover science instruments. "We suspect it might be a volcanic explosion crater, and that's something we haven't seen before."
A light-toned ring around the inside of the pit might add information about a nearby patch of bright, silica-rich soil that Squyres counts as Spirit's most important discovery so far. The rover churned up the silica in mid-2007 with an immobile wheel that it has dragged like an
anchor since it quit working in 2006. The silica was likely produced in an environment of hot springs or steam vents.
For Opportunity, the next major destination is Endeavour Crater, approximately 22 kilometres (14 miles) in diameter, more than 20 times larger than another impact crater, Victoria, where this rover spent most of the past two years. Although Endeavour is about 12 kilometres (seven miles) from Victoria, it is considerably farther as the rover drives on a route evading major obstacles.
Since climbing out of Victoria four months ago, Opportunity has driven more than a mile of its route toward Endeavour and stopped to inspect the first of several loose rocks the team plans to examine along the way. High-resolution images from NASA's Mars Reconnaissance Orbiter,
which reached Mars in 2006, are helping the team plot routes around potential sand traps that were not previously discernable from orbit.
"We keep setting the bar higher for what these rovers can do," said Frank Hartman, a JPL rover driver. "Once it seemed like a crazy idea to go to Endeavour, but now we're doing it."
Squyres said, "The journeys have been motivated by science, but have led to something else important. This has turned into humanity's first overland expedition on another planet. When people look back on this period of Mars exploration decades from now, Spirit and Opportunity may be considered most significant not for the science they accomplished, but for the first time we truly went exploring across the surface of Mars."
• For the latest news and more information on the mission visit the official NASA
site
, it is authored by the BBC Natural History Unit, edited by Karen Bass and has an introduction by Brian Leith.
