NASA hopes opportunity, now at the rim of the Victoria crater, will descend into the crater after the storm passes

Officials at the U.S. space agency NASA say the Mars rovers Spirit and Opportunity remain hunkered down beneath Martian skies darkened by severe dust storms. The unusual weather has lasted for weeks, and the vehicles' human controllers are trying to keep the rovers warm despite the lack of light on their solar power cells.

In more than three years on the Martian surface, the twin rovers have never experienced these near-blackout conditions, says rover project manager John Callas.

"Right now as of today, the weather is actually getting worse for Spirit and has been fairly stable for Opportunity," he told VOA. "Opportunity had experienced some really bad weather last week, which had given us some concerns. It's moderated a little bit, but now the weather is getting worse for Spirit."

Callas says the dust storms are at high altitudes. The rovers are not being buffeted by winds or blasted by driving sand, but the overcast conditions are preventing their solar cells from generating enough power. He says they're only getting as much sunlight as you would get on a very dark, stormy day here on Earth, with only about one percent of normal light that the rovers can turn into electricity.

To help conserve energy, controllers at NASA have powered down most of the rover systems, which saves power but means the rovers' electronic equipment isn't throwing off any heat. They should be able to withstand temperatures as low as minus 40 degrees (Celsius), but temperatures are plunging down to minus 60 or 70.

"At night, when it gets cold, we need to have some energy going into the electronics box just to keep [the equipment] warm," Callas explained. "If we don't have any energy it could get too cold. If it gets too cold something could break."

In another power-saving move, he says the rovers are communicating less frequently with Earth, just once every three days or so for Opportunity.

"It takes energy to communicate and so we want to save as much energy as possible although we're always uncomfortable when we go a day without listening to our rovers, but right now we feel the best allocation of the limited power is just to communicate once every three days with Opportunity."

Spirit and Opportunity were originally to have explored the Martian surface for about three months. Their mission has now lasted more than three years. Rover project manager John Callas says the rovers are among several spacecraft now on the Martian surface and circling overhead, that provide complementary information for scientists trying to learn more about the Red Planet. The next spacecraft heading for Mars, the Phoenix lander, is set to be launched on August 3.