The Spirit Rover, which has been exploring the Red Planet’s surface for almost five years, is now threatened by dust covering its solar arrays, which is gathering in greater quantities due to massive dust storms on Mars’ surface. The rover is dangerously low on power.

The last time Spirit communicated with Earth was on Sunday, when the craft reported that the solar arrays which power it had produced only 89 watt-hours of energy. That is much less than usually required by Spirit in a day.

That value is also the lowest amount of energy that Spirit or its counterpart, Opportunity, have produced in the entire lifetime of the Martian mission which has started in January 2004.

Rover project manager John Callas of the Jet Propulsion Laboratory in La Cañada Flintridge told press that the survival of the rover may be endangered due to the arrays producing only a third of the power they should be, due to the dust; and this was before the latest dust storms hit Spirit. Occurring over the last few days, the storms further reduced the energy output to 26.5%, says Callas.

Spirit’s problems have been announced a day after NASA’s announcement of the Phoenix mission’s end. The Phoenix was a static lander deployed near Mars’ North Pole, and was the first such instrument to sample ice on the planet. Dust storms and the encroaching winter at the high latitude are responsible for the Phoenix shutting down.

Callas also says that the low power levels have probably activated a built-in protection system in the rover, which automatically disconnects almost all of Spirit’s electronics from batteries, in order to prevent complete drainage.

When a low-power-shutdown occurs, mission control on Terra loses control of the vehicle. Normally, after such a shutdown, the rover does periodic checks of whether the batteries have recharged, and resumes operations when they do.

Invoking the worst-case scenario, callas says that "The best chance for survival for Spirit," is to avoid the case where Spirit might not awake from a low-power shutdown.

To prevent draining Spirit’s batteries, mission managers have ordered the rover through a message to not communicate with Terra until Thursday. NASA hopes that by then the dust storms will have cleared enough to allow the solar panels to produce more power.

The rover is currently stationary on a geographical feature called the Home Plate, which is located in the Gusev crater on Mars’ southern hemisphere.

Spirit’s sister rover, the Opportunity, which has not been compromised by the dust storms as much as its counterpart, is driving to a deep crater. Both of the rovers originally had life expectancies of 90 days, which they have far outlasted.

In the time they’ve spend on mars, they have drilled into rocks and taken pictures of erosion patterns. Their findings have proved that Mars was once, in large parts, covered by seas and lakes. Nowadays it’s much too cold for water to exist as a liquid.

The rovers’ current mission is to tell how the planet changed from a temperate world to the barren rock that it is today.