After the massive dust storm that nearly killed them, both Opportunity and Spirit are resuming scientific investigations, NASA reported.
The dust storm that lasted for more than two months has left deep scars on the rovers, but amazingly they are still able to continue their separate Mars missions. According to NASA, Opportunity's planned descent into the giant Victoria Crater was delayed, but now the rover is preparing to drive into the half-mile diameter crater as early as Sept. 11.
In July, NASA had announced that dust storms has blocked 99 percent of direct sunlight to the rover Opportunity and the Spirit is also affected, but to a lesser extent.
Dust storms are quite usual on Mars and their intensity sometimes reaches planetary levels (like the one just witnessed by both Spirit and Opportunity, which is the worst since their arrival in 2004), literally covering the entire celestial body in a thick, dark garment. Such storms pose a great risk to Opportunity’s sensitive mechanics and force the postponement of scientific investigations.
The tiny dust particles were blocking the sunlight from reaching the rovers’ solar panels, thus causing energy shortages and forcing scientists on Earth to delay Opportunity’s long-expected descend inside Victoria crater. Opportunity had to be put on stand by, with low-energy functioning and data transmissions at interval of three days, after the record levels of dust reported by the tiny machinery at the end of July, when the air's opacity rose from 1.0 to 3.3. Due to the huge dust storm, solar array energy on the rover dropped from 765 watt-hours to 402.
This particularly concerned NASA because Opportunity is extremely vulnerable to any energy leak: a heater switch that has been stuck in the "on" position since landing day in January 2004 is continuously draining precious power from it.
Good news however emerged recently though, when NASA’s scientists also reported that Spirit, Opportunity's rover twin, survived the global dust storm and that it is heading towards its long-term destination called Home Plate, a plateau of layered bedrock bearing clues to an explosive mixture of lava and water.
Scientists are particularly thrilled by Opportunity and Spirit’s performances, since they were only scheduled to work for about 3 months after their landing. Paradoxically, what helped most were the winds that on one side have been hindering the mission (by carrying dust particles in the upper levels of the Martian atmosphere), but on the other have also been clearing the solar panels periodically in the rovers’ short life on Mars.
"These rovers are tough. They faced dusty winds, power starvation and other challenges -- and survived. Now they are back to doing groundbreaking field work on Mars. These spacecraft are amazing," said Alan Stern, associate administrator of NASA's Science Mission Directorate, Washington.
Opportunity had reached Victoria Crater’s edge in June and was programmed for descent on June 27, when the storm formed. The descent was further delayed by the need to find a suitable sliding place, and for that the rover had to circle around Victoria. That crater is so important because it contains an exposed layer of bright rocks that may preserve evidence of interaction between the Martian atmosphere and surface from millions of years ago, when the atmosphere might have been different from today's. Victoria is the biggest crater Opportunity has visited.
According to NASA, Opportunity drove to the lip of Victoria Crater in late August and examined possible entry routes. This week, Opportunity has been driving about 130 feet toward its planned entry point. The route will provide better access to a top priority target inside the crater: a bright band of rocks about 40 feet from the rim.
"We chose a point that gives us a straight path down, instead of driving cross-slope from our current location," said Paolo Bellutta, a JPL rover driver plotting the route. "The rock surface on which Opportunity will be driving will provide good traction and control of its path into the crater."
For the descent into the crater, Opportunity needs some preparations, which will be coordinated from Earth. It first needs to get its six wheels in and then back out and assess slippage on the inner slope.
"Opportunity might be ready for that first 'toe dip' into the crater as early as next week," said JPL's John Callas, rover project manager. "In addition to the drives to get to the entry point, we still need to conduct checkouts of two of Opportunity's instruments before sending the rover into the crater."
One of the problems that need to be solved in the following period is related to the proper functioning of the microscopic imager, which seems to have been damaged. If it still works, it should help NASA’s engineers figure out whether another tool, called miniature thermal emission spectrometer (Mini-TES) is indeed displaying pictures of the Martian soil or images from rover's camera mast.
"If the dust cover or mirror is no longer moving properly, we may have lost the ability to use that instrument on Opportunity," said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science instruments. "It would be the first permanent loss of an instrument on either rover. But we'll see."
"Mini-TES has told us a lot about the rocks and soils at Meridiani, but we've learned that the differences among Meridiani rocks are often too subtle for it to distinguish," Squyres said. "The same instrument on Spirit, at Gusev Crater, has a much more crucial role for us at this point in the mission because there is such diversity at Gusev."
Researchers will rely heavily on a different type of instrument, Opportunity's alpha particle X-ray spectrometer, for analysis of rocks at the bright-band target layer in the crater.
