Mission scientists worry that nearly a month's worth of storms could permanently damage or disable the Mars rovers exploring the Red Planet.
A series of severe Martian summer dust storms has blocked 99 percent of direct sunlight to the rover Opportunity. Its companion, Spirit, has been affected to a lesser extent. Both rely on solar panels to charge their batteries.
Scientists believe the storms could continue for several days, or even weeks.
"We're rooting for our rovers to survive these storms, but they were never designed for conditions this intense," Alan Stern, associate administrator of NASA's Science Mission Directorate, said in a news release posted Friday on the space agency's Web site.
The rovers will not be able to generate enough power to keep themselves warm and operating under reduced sunlight for much longer, NASA said.
Before the dust storms, Opportunity's solar panels had been producing about 700 watt hours of electricity per day. The dust reduced the daily output to less than 400 watt hours, prompting the rover team to suspend driving and most observations. On Wednesday, Opportunity's solar-panel output dropped even further, to 128 watt hours.
The rovers have been exploring Mars since landing in 2004 for a mission originally planned for three months.