The plucky Mars rover vehicles still are clinging to life amidst a bitterly blinding dust storm on the red planet, but their health is touch-and-go.

Even if the rovers take substantial time to return to health, or suffer a worse fate, they already have lasted far longer than intended.

NASA reported that engineers are growing increasingly concerned about the temperature of vital electronics on Mars Exploration Rover Opportunity, while the rover stays nearly inactive due to a series of dust storms that has lasted for more than a month.

Dust in the atmosphere and dust settling onto Opportunity’s solar panels challenge the ability of the solar panels to convert sunlight into enough electricity to supply rover needs for heating during cold nights, and planned operations.

It was a disappointing time for the huge dust storms to hit the rovers, because Opportunity was on the verge of potentially significant findings. It was on the edge of Victoria Crater, about to begin descent to the crater floor. On the way down, Opportunity was going to stop at an interesting rock outcropping that might have given NASA engineers and scientists vital clues as to the early surface of Mars, and told whether water flowed on the planet long ago.

The most recent communication from Opportunity, received a week ago, indicates that sunlight over the Opportunity Meridiani Planum location remains only slightly less obscured than during the dustiest days Opportunity survived in mid-July.

With dust now accumulating on the solar panels, the rover is producing barely as much energy as it is using in a very-low-power regimen it has been following since July 18.

Keeping its activity to a minimum has reduced the amount of energy going into the rover electronics core, reducing the amount of heat that comes from the electronics components themselves during normal operation.

“The overnight low temperature of Opportunity’s electronics module has been dropping since we implemented the very-low-power operation, even though the outside environment is actually warmer during this dust storm,” said John Callas, rover project manager at the NASA Jet Propulsion Laboratory in Pasadena, Calif.

That temperature has dropped to minus 35 degrees Fahrenheit (minus 37 Celsius), within about 3 Fahrenheit degrees (about 2 Celsius degrees) of triggering survival heaters.

Those heaters could push total rover electricity use higher than what the solar panels produce, soon depleting the batteries.

“This is energy Opportunity does not have to spare,” he said.

To forestall the survival heaters from turning on, the rover team has altered Opportunity’s daily regimen to keep the electronics active for a longer period each day. This, too, could put the rover through some negative-net-energy days if the sky does not begin to clear.

Callas said, “This means there is a real risk that Opportunity will trip a low-power fault sometime during this plan. When a low-power fault is tripped, the rover’s systems take the batteries off-line, putting the rover to sleep and then checking each sol [Martian day] to see if there is sufficient available energy to wake up and perform daily fault communications. If there is not sufficient energy, Opportunity will stay asleep. Depending on the weather conditions, Opportunity could stay asleep for days, weeks or even months, all the while trying to charge her batteries with whatever available sunlight there might be.”

Spirit, meanwhile, also is accumulating some dust on solar panels under a sky at Gusev Crater that remains nearly as dusty as the worst Spirit has recorded.

“We will continue to watch the situation on Mars and do all we can to assist our rovers in this ongoing battle against the environmental elements on the Red Planet,” Callas said.