A powerful dust storm on Mars is affecting two roving robots' operations on the Red Planet.
The storm, which has been brewing for a week, has partially blocked the sun. The rovers, Spirit and Opportunity, rely on sunlight to charge their batteries.
Scientists maintain that the robots, which have operated before at low power levels, are not in danger.
The regional storm is the worst to hit the rovers since they landed on opposite ends of Mars in 2004, and scientists expect the storm to last for at least another week.
"The storm is affecting both rovers and reducing the power levels on Opportunity," project manager John Callas of NASA's Jet Propulsion Laboratory said in a statement posted on the space agency's Web site.
Opportunity scaled back operations on June 30 to conserve energy.
The storm has already delayed Opportunity's descent into Victoria Crater to learn more about the planet's geologic past. Scientists hoped to send the rover into the crater this weekend, but weather has pushed the entry until at least July 13.