The Opportunity rover photographs its shadow on Mars.NASA / JPL

For weeks, Michael Staab has slept with his cell phone on his nightstand, its ringer set to the highest volume, waiting for a call from Mars.

Staab, an engineer at NASA’s Jet Propulsion Laboratory (JPL), in California, is leading the recovery effort for one of the agency’s Mars rovers, Opportunity. The nearly 15-year-old rover went silent in mid-June as a record-breaking dust storm swept across the planet. As the atmosphere swelled with dust, sunlight couldn’t reach the rocky valley in Mars’s southern hemisphere where Opportunity resides. The solar-powered rover couldn’t charge its batteries in the stormy darkness, so it slipped into a quiet sleep.

Engineers at JPL have spent the summer trying to wake it up. The Deep Space Network, a collection of massive radio antennas that communicates with spacecraft throughout the solar system, spends hours a day listening to Mars. The engineers use the network to relay commands to the rover, instructing it to send back a beep. In the past several weeks, the dust storm has abated and the skies have begun to clear. But the engineers haven’t heard anything. If the silence continues, they may soon be forced to give up.

“We hope to share good news soon,” Staab says, “because we’re all going stir-crazy.”

On Thursday, NASA announced it had set a deadline for the current recovery attempts for the rover. According to atmospheric data from a NASA orbiter around Mars, there will soon be enough sunlight reaching the surface for Opportunity to recharge its batteries and kick off some automated procedures to bring it back online—if it survived the storm in the first place. When that happens, the countdown begins.

“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,” said John Callas, the Opportunity project manager, in a press release. “At that point, our active phase of reaching out to Opportunity will be at an end.”

JPL said engineers will undertake “passive-listening efforts” for several months beyond that. Instead of sending commands to the rover, the Deep Space Network will listen to the frequencies transmitted by all the spacecraft on and around Mars, and engineers will check the recordings for Opportunity’s specific frequency. There’s a chance that Opportunity’s solar arrays may be caked in dust, which would prevent the rover from powering its batteries, regardless of the amount of sunlight present. But “the chances are small that dust accumulation would be the root cause of Opportunity’s lack of communication,” JPL said Thursday.

The decision has prompted an outcry from some current and former members of the Opportunity team who don’t agree with NASA’s recovery plan. They point out that NASA tried harder with Spirit, which landed on Mars with Opportunity in 2004. When the rover went silent in 2010 during extreme winter conditions, engineers spent 10 months actively listening for its calls, and then another five on passive efforts. Spirit never woke up.

“I still can’t make an engineering case [for] not giving Oppy a chance. We tried everything for Spirit. Why not for Opportunity?” Mike Seibert, a former Opportunity flight director, tweeted. Seibert authored a paper in 2009 describing how Opportunity and Spirit survived the 2007 dust storm.

Current members of the team seem just as confounded. “We don’t know where the 45-day number came from,” said one Opportunity team member, who spoke on the condition of anonymity because he was not authorized to speak to the press. “It is not a recommendation the engineering team made to project management.”

Rumors had swirled at JPL this week that officials were making such preparations for the end of Opportunity’s mission, according to another member of the Opportunity team, who spoke on the condition of anonymity because she was not authorized to speak to the press. The Opportunity team did not receive formal notice about the plans until minutes before JPL published its press release Thursday afternoon, she said.

“It’s made its way around to more than a few people at this point, which makes me surprised that no official statement has actually been made to the team yet as to what’s going on,” she said when we spoke early Thursday. “The people that have heard about it on the Opportunity team are like, what’s going on? And not getting an answer from anybody. It’s making everybody a little bit worried.”

This Opportunity staffer said the rumors prompted several of her colleagues to begin tweeting in support of Opportunity earlier this week, in an attempt to show JPL leadership that the rover is popular and beloved by the public. Starting Tuesday night, tweets featuring #WakeUpOppy and #SaveOppy started cropping up. A JPL spokesperson told me they did not know what prompted the sudden grassroots campaign.

“The campaign got a lot of attention from the higher-ups,” this Opportunity staffer said, “which is good. That was the intent.”

When the new recovery plan was made public, there was “a lot of anger, some sadness, some shock” among members of the team, she said.

NASA officials came to this conclusion based on their understanding of how opaque the Martian atmosphere is, a measure known as tau. The greater that value, the less sunlight permeates the atmosphere to reach the surface. Before it went silent, Opportunity’s instruments recorded a tau of a 10.8—far greater than the usual tau in the southern hemisphere, which oscillates between 1 and 2. (During the last big dust storm on Mars, in 2007, the tau barely topped 6.)

Without Opportunity, NASA has relied on an instrument on the Mars Reconnaissance Orbiter to provide measurements of the tau. They’re less precise, but they provide good estimates. According to the orbiter’s latest measurements, tau is now at 1.7. JPL officials believe that when that level dips to 1.5, there should be enough sunlight peeking through the atmosphere to let Opportunity charge. That’s when they’ll start the clock.

Former and current Opportunity team members and others say the 45-day period is not long enough to account for the potential of atmospheric phenomena known as dust-cleaning events. In the past, dust devils have swept away grains on Opportunity’s solar arrays. Sometimes, the wind was so effective that the panels were restored to their original sheen.

“I think our best hope has nothing to do with how much dust you estimate is in the sky. I think our best hope for the rover is when it gets windy, the dust blows off,” says Mark Lemmon, an associate professor at Texas A&M University who works on daily operations of the Opportunity rover. “That has happened reliably and repeatedly with Opportunity, and the season for that is approaching.” Such dust-cleaning events are common between November and late January.

Engineers have carried out simulations predicting Opportunity’s current conditions. But they can’t account for how much dust remains—if any—on Opportunity’s solar panels. “The initial results [of the simulations] suggest that if tau was below about 1.5, there is a chance, depending on the dust loading on the panels, that we would be able to hear from Opportunity,” says Matt Golombek, the project scientist for the Mars Exploration Rover mission, which covers Opportunity and the now-defunct Spirit. “Although we have an estimate of the dust in the atmosphere, we have no idea how much dust is on the panels.”

Golombek, Staab, and others involved in recovery efforts say they haven’t given up on Opportunity.

“There’s nobody here who’s discouraged yet,” Golombek says. “We’re all pretty optimistic that with time we will regain communication with the rover.”

The tau on Mars should reach 1.5 within weeks, Lemmon says. Even if engineers detect a ping from Opportunity, it may take weeks before they hear another one. Because the rover has been without power for so long, the onboard clock may have failed. When it wakes, Opportunity won’t know what time it is, which means it won’t know when it should attempt to communicate with Earth. It’s possible the rover will attempt to call home when the Deep Space Network is not listening. “It may take weeks or even longer to actually get control of the spacecraft again,” Golombek says.

If engineers are able to regain steady communication with Opportunity, they will ask the rover to send information about its vitals. They’ll even ask the rover to use its camera to take selfies, so that engineers can see how its exterior fared in the storm. NASA says that after engineers assess the rover’s health, they’ll take a poll to determine whether they should attempt a full recovery.

But if the silence continues, even as the skies grow clear, NASA will eventually have to call off the rescue. After nearly 15 years, Opportunity’s work on Mars will come to an end.

The loss will not be considered a failure. When Opportunity and Spirit touched down on Mars, their stewards expected the rovers to last just 90 days. Their goal was to get the lay of the land, zap some holes into the rust-colored terrain, and send home information about the composition of an alien world. But they proved to be hardy space robots. They survived the harshest temperatures of Martian winters. They kept trekking even as some of their wheel motors malfunctioned; Spirit spent six years driving backward after its front wheel stopped working. Opportunity and Spirit showed that it’s pretty hard to kill a Mars rover.

Opportunity’s lengthy mission has given its engineers and scientists plenty of time to form deep, emotional attachments to the rover. For them, Opportunity is something more than fused metal and circuitry. It is an extension of humanity, a hardworking field scientist doing a job they can’t do themselves. Their attachment is so strong that they’ve mourned its silence the way they would a human being. Project managers have likened keeping watch over Opportunity to sitting vigil next to a coma patient.

And the pain of waiting is getting worse. “The fact that it’s now been over 70 days that we’ve last heard from her—we’re starting to feel it,” says Keri Bean, a science planner on the Opportunity mission who is training to be a rover driver.“There are definitely some good days and there are some bad days. All of our analysis shows that eventually she’ll come back, but sometimes I’ll have dreams in the middle of the night. I’m standing there on Mars next to her, and wiping the dust off her lenses.”

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.