Summer dust storms on Mars are causing problems for NASA's twin Mars exploration rovers, blotting out the sunlight they need to recharge their batteries and threatening their operations on the red planet.
Although NASA scientists and engineers are evaluating the problem, there's apparently not much they can do but wait out the four-to-six-month-long dust storm season.
In an announcement Friday, NASA said that dust storms hitting the Opportunity rover in the planet's southern hemisphere for the last month have blocked as much as 99 percent of the sunlight in the atmosphere, drastically reducing the amount of energy that can be generated and stored by the rover's solar collection panels and batteries.
For Opportunity, and its sibling rover Spirit on the other side of the planet, the storms have meant cutbacks in operations as the devices try to conserve power until the storms dissipate, said Jake Matijevic, engineering team chief at NASA's Jet Propulsion Laboratory at the California Institute of Technology in Pasadena. By reducing rover activity and data transmissions to Earth, NASA has been able to lower the power consumption on the rovers to conserve energy.
"It appears as though we're going to be OK for the foreseeable future," Matijevic said. But if the storms persist and the solar panels can't collect enough sunlight to fully recharge the batteries, the future of the rovers would be in doubt. Summer dust storms on Mars are common, and are especially strong about every six years, he said. The last period of major storms was in 2001.
Past storms on Mars have affected the rovers, too, but those were only short-term events, Matijevic said.
Typically, the solar panels produce about 700 watt hours of electricity per day for each rover -- enough to light a 100-watt bulb for seven hours, according to NASA. But the dust storms have reduced that to as little as 128 watt hours per day. When daily power generation is down to less than 400 watt hours, the rovers suspend their driving on the planet and stop using their robotic arms, cameras and other instruments, NASA said.
"Clearly, if the batteries completely discharge, then there's little chance to get the vehicles back, but it doesn't appear that way," Matijevic said. "I think we'll ride this out until our skies clear."
Because there's no way to upgrade the solar collection systems on the rovers, there is little IT can do to fix the problem. One suggestion has been to tilt the solar collection panels on the rovers more toward the sun, but the dust is so dense in the atmosphere that the effect would be minimal, he said.
If the batteries completely die, heating systems on the rovers that keep sensitive electronic parts within a safe temperature range would fail, leaving the rovers so cold that their onboard electronics would likely be ruined. The rovers are certified for operating temperatures as low as -40 degrees Fahrenheit, while the low temperatures on Mars can plummet to as much as -103 degrees Fahrenheit, Matijevic said.
The two rovers, which landed on Mars three weeks apart in January 2004, were designed to collect information, perform experiments and travel the planet for 90 days. Instead, they have collected data on Mars for more than three years, giving scientists and researchers a wealth of information.
A few weeks after landing, the Spirit rover suffered computer memory issues that were later resolved; two months later, they needed operating system updates to improve their performance. Last year, the Spirit had a problem with one of its six wheels, but that also was dealt with, allowing the mission to continue.
"My own prediction is if they can get through this dust storm season, then they're probably good for another year," Matijevic said.