NASA's Mars rover known as Opportunity has been on Mars nearly 15 years, a wee bit longer than the 90 days it was originally designed for.
It has traveled 28 miles on the surface, taken thousands of images, and improved scientists' understanding of the red planet.
But NASA hasn't heard from the plucky rover since June.
"I have to admit I'm beginning to be a little bit worried," says Bill Nelson, engineering manager for the rover. "I thought about now was when I would have expected to hear from the vehicle."
Nelson says an intense dust storm that started back in May almost completely blotted out the sun. The rover's solar panels couldn't generate the power the rover needs to operate. When that happens, the rover is designed to put itself to sleep.
When the sun comes back, the rover should wake up and transmit a signal to Earth, but it hasn't.
"It needs to have a certain minimum threshold of energy, and we believe it's not getting to that," Nelson says. It may be the storm covered the solar array with so much dust that "it's not able to really recharge up to a level that would allow it to operate."
For the past few weeks, mission managers have been trying a different tactic. Instead of passively waiting for the rover to wake up on its own, they're pinging the rover with commands. The idea is that it might be waking up, but going back to sleep before it can transmit a signal.
It takes about six minutes for a radio signal to travel to Mars, and another six minutes to come back.
"Around 12 minutes from the time we sent the command is when we would expect to hear back from the rover," says Ashton Vaughs, Opportunity Ace. The "Ace" is the one who actually presses the button that sends commands to the rover via the Deep Space Network, a collection of large radio antennas around the world.
If the rover does send back a signal, Vaughs would be the first to hear it.
"We trust that he would share that information rapidly," Nelson says.
Not hearing anything has been unsettling for the scientists and engineers working on Opportunity.
"Right now we're in this state of limbo, says Abigail Fraeman, deputy project scientist. "What's going to happen next, we don't know."
Fraeman has a long history with the rover. In 2004, when she was 16, she was in a Jet Propulsion Laboratory control room when Opportunity landed. JPL is where the mission is managed. She was there as part of an outreach program called Red Rover Goes to Mars run by the Planetary Society.
She says even if the rover is never heard from again, it's important to remember it was only expected to last 90 days.
"It's accomplished so much more than we even could have imagined," says Fraeman. "I mean the fact that I was able to be in the room when it landed when I was in high school, and now I got my PhD, I'm at JPL and I'm the deputy project scientist just tells you how long this has been running, and how much has happened, and so it's sad, but it's not terribly sad. It's terribly happy how wonderful the mission has been."
The team working on Opportunity is treating the rover's silence not as a problem, but as an opportunity.
Ashley Stroupe is a rover driver. She designs the commands for moving the rover's robotic arm on Mars. She's part of a team that was building new software packages for the rover when it went silent.
"We're at least taking advantage of the downtime to finish all that up, so that when, we'll say 'when,' Opportunity talks to us again we'll be ready to go," she says.
You can call that Opportunity optimism.
Copyright 2024 NPR
