A global dust storm has been raging on Mars since June.

The Opportunity rover began hibernating on June 10 to wait out the storm, but it has yet to wake up and call NASA.

If the robot can't get enough sunlight, its batteries may lack the electricity to power heaters, and the b listering cold on Mars can snap electronic circuits.

NASA will give Opportunity 45 days to wake up once the dust settles, but end the mission if it does not get any signal after that time.

A global dust storm on Mars is threatening the future of NASA's Opportunity rover, the longest-lived machine on the red planet.

The golf-cart-size robot launched toward Mars in June 2003, landed in January 2004, and was supposed to last 90 days. Now the rover is 15 years old and has rolled more than a marathon's worth of miles across the Martian surface using solar power.

But Opportunity is now in a life-or-death struggle, and NASA may ultimately choose to give up on the rover.

Because of the long-lasting dust storm, which has now raged on Mars for nearly two months, Opportunity fell asleep on June 10 and hasn't phoned home since. Global dust storms appear once every couple of years on the red planet, shrouding it in a dull-red haze, but NASA said this was "one of the most intense" ever recorded.

"This is the worst storm Opportunity has ever seen, and we're doing what we can, crossing our fingers, and hoping for the best," Steve Squyres, a planetary scientist at Cornell University and leader of the rover mission, told A.J.S. Rayl for a June blog post at the Planetary Society.

More recently, NASA said the dust should soon clear.

"The sun is breaking through the haze," John Callas, the rover's project manager at NASA's Jet Propulsion Laboratory, said in a press release on August 30. "Soon there will be enough sunlight present that Opportunity should be able to recharge its batteries."

However, once that moment arrives — perhaps a week or two from now — the space agency will begin a countdown timer to the rover's presumed death.

"If we do not hear back after 45 days, the team will be forced to conclude that the sun-blocking dust and the Martian cold have conspired to cause some type of fault from which the rover will more than likely not recover," Callas said.

This deadline, which will likely happen in late October, will mark the end of an "active" campaign to contact Opportunity. But Callas said NASA won't entirely forsake the rover: The agency will still try "several months" of "passive listening" to see if the robot somehow wakes up.

Why the dust storm is endangering Opportunity

Mars in 2001 as it typically appeared (left) and how the red planet looked after a global dust storm appeared (right). NASA/JPL-Caltech/MSSS

The Martian weather event not only blocked light to Opportunity's solar panels, but also coated them in fine dust. This one-two punch dramatically lowered the rover's ability to store and use electrical energy.

Cold is a big issue on Mars, where winter temperatures can drop to -100 degrees Fahrenheit near the equator. Such cold can shrink bits of metal in electronic circuits and snap them.

Little buttons of nuclear material called plutonium-238 help keep Opportunity's circuitry warm, but the stuff doesn't last forever and is well-decayed — so it's not hot enough to fully protect the rover's systems. This means Opportunity still needs electricity to keep its battery charged, run circuit-warming heaters, and talk to NASA mission control.

Draining the batteries too low is also problematic. The longer they're inactive, the more electrical storage capacity they lose. If the dust doesn't get blown off Opportunity's solar panels soon, NASA has said there's a possibility the batteries could "brown out," or suddenly dip in voltage.

If that happens, or the rover can't recover a variety of "fault modes," Opportunity will join the ranks of Spirit — its nearly identical sister rover. Spirit stopped talking to NASA in March 2010, during a Martian winter.

Engineers tried to regain contact with Spirit for more than a year before calling it quits. (Spirit is now presumably another dead robot on the red planet.)

The good news — and bad news — of a weakening dust storm

NASA has said "there's reason to be optimistic," since the storm is weakening. This could mean enough sunlight may soon hit Opportunity's solar panels to charge up its batteries and phone home.

The agency also said that the batteries were in "relatively good" working condition before the storm, so "there's not likely to be too much degradation."

Dust storms also tend to warm up the environment, so that may help buffer against circuit-busting cold. And for a few months, starting around November on Earth, dust-devil season should begin on Mars and increase the chances that a whirlwind will clear the rover's solar panels.

Still, this is one of the longest periods a solar-powered robot has ever hibernated on Mars to conserve energy, and a dissipating storm means surface temperatures will soon drop. The rover has also pushed its engineered lifetime by a decade and a half.

"Even if engineers hear back from Opportunity, there's a real possibility the rover won't be the same," NASA said. "No one will know how the rover is doing until it speaks."

'We tried everything for Spirit. Why not for Opportunity?'

For now, NASA is watching the Martian skies from above using an orbiting satellite. But Opportunity will soon face a seemingly arbitrary deadline set by NASA.

The agency is waiting for "tau" levels — a measure of darkness caused by dust in the air — to drop to 1.5 or less before starting its countdown for Opportunity to wake up. (Tau levels for the rover reached nearly 11 during the height of the dust storm.)

These images simulate the "tau" or darkness of the Martian sky as seen by NASA's Opportunity rover during a global Martian dust storm blotted during the summer of 2018. Left to right: Tau 1, 3, 5, 7, 9, and 11. NASA/JPL-Caltech/TAMU

"Assuming that we hear back from Opportunity, we will begin the process of discerning its status and bringing it back online," Callas said.

But giving the rover just 45 days to wake up has upset some scientists on the team, according to The Atlantic.

That story points out that Spirit was given 10 months of "active" listening, in which a network of NASA spacecraft and radio antennas tried to contact the rover. That was followed by five months of "passive" listening, when the same network occasionally tried to detect an "I'm alive" signal. In total, that's about 15 months — nearly a year longer than NASA plans to give Opportunity.

It's possible that the deadline for Opportunity may be NASA's way of trying to end the mission, ostensibly to free up staff and resources for future space missions.

Mike Seibert, who is a former flight director for the Opportunity rover, weighed on on the plan on Twitter.

"I was there when we sent the last [official] command to try and restore contact with Spirit. I was there when we sent the last unofficial commands weeks later using a different set of commands," Seibert said. "We tried everything for Spirit. Why not for Opportunity?"

This story has been updated with new information. It was first published on August 26, 2018.