Opportunity’s watch has ended.
Tuesday night, engineers at NASA’s Jet Propulsion Laboratory sent one last round of commands to the plucky little rover; no response would come. NASA officially declared its beloved Opportunity rover lost, broadcasting the announcement from the agency’s Jet Propulsion Laboratory in California.
“I was there yesterday and I was there with the team as these commands went out into the deep sky,” said NASA associate administrator Thomas Zurbuchen during Wednesday’s briefing. “And I learned this morning that we had not heard back and our beloved Opportunity remained silent.”
Opportunity, a golf-cart-sized rover on Mars, has been unresponsive since June when a global dust storm enveloped the planet, blotting out the sun’s light. The storm was the worst on record in the four decades that robots have occupied Mars. It raged on for months, darkening the sky and starving the little rover of the life-sustaining energy it needed to keep its batteries charged. But NASA remained hopeful, expecting that once the storm subsided, the rover might wake up. However, as the months passed and commands went unanswered, that hope started to fade.
Many attempts were made to resuscitate the rover, yet none were successful. After eight months of silence, agency officials made the tough call and declared the rover dead. “I stand here surrounded by the team and I have to tell you, it’s an emotional time,” Zurbuchen added. “I am standing here with a sense of deep appreciation and gratitude that I declare the Opportunity mission as complete.”
The rover team is nostalgic, simultaneously mourning the loss of their robot while celebrating its tremendous achievements. “Yes the project is about a robot, but that robot was built by people. People are what make it,” John Callas, the Mars Exploration Rover program manager said during the briefing. “Nineteen years ago, they were given a task that many thought was impossible. Instead of being just 90 days, it turned out to be more than a decade long adventure, and that is because of those engineers.”
Opportunity and its twin, Spirit, launched 15 years ago, touching down on opposite sides of Mars. They were tasked with finding evidence of water (and perhaps, even life) on the red planet. Together, the twin rovers—formally known as Mars Exploration Rovers (MER) A and B—brought the red planet to life in a way no other robotic explorers had.
Steve Squyres, the mission’s principal investigator of Cornell University, explained that Opportunity’s prime mission was expected to be more like a quick survey of the small area surrounding its landing site rather than the planet-trekking expedition it turned into. Both Opportunity and Spirit went on adventure after adventure, far exceeding their predicted 90-day lifespan.
The dynamic duo were remote geologists, studying the rocks that humans couldn’t reach. “Geology is a forensic science,” Squyres explained. “Something happened at this place on Mars billions of years ago, and we want to know what it was.”
“The clues are in the rocks, [and the] rovers were equipped with tools to uncover those clues,” he added.
Mars today is a cold, dry, desolate world; a place where not much happens. But that was not the case long ago—it was a hot, violent, steamy place. There was a plethora of geologic activity, lots of impacts, volcanic explosions, profound evidence for hydrothermal activity, hot springs, etc. “It sounds like a scary place, but is also the kind of place that would be suitable for life,” Squyres said. “It was habitable.”
Spirit and Opportunity may be gone, but they left us a legacy. The little rovers that could gave us 14 incredible years of phenomenal exploration. But how did Opportunity last this long? Incredible engineering and perhaps a bit of luck.
NASA engineers know what they’re doing when it comes to building robots. Opportunity’s battery lasted more than 5,000 charge cycles and was at 85 percent capacity when the rover died. “These rovers actually have the finest batteries in the solar system,” explained Callas. “We’d all love it if our cell phone batteries lasted this long.”
Mars is a dusty place and before launching the rovers, NASA anticipated that dust could be the mission-ending factor. They expected that dust would collect on the rover’s solar arrays, cutting off power after the 90-day mark. But fortunately for the rovers, Mars is also a windy place. Seasonal winds would clear off the solar panels, allowing the rovers to remain operational through the harsh Martian winter. However, the dust proved to be too much in the end for Opportunity.
So what happened?
During the briefing, Callas offered some insights. The dust storm that enveloped most of Mars last June was one for the record books. Day looked like night, and that spells doom for a solar-powered robot. The lack of light meant Opportunity couldn’t charge its battery. But the real culprit behind its demise could have been the same clever engineering trick that kept it running for so many years.
Not long after Opportunity landed, engineers realized that a heater in its robotic arm was stuck in the on position. Unable to turn it off, their solution was to shut down the rover’s power systems every night. This allowed Opportunity to stay just warm enough that it could survive until the sun came up the next morning. This process was repeated daily.
But the life-saving fix, coupled with the biggest dust storm on record, may have spelled doom for the plucky little rover.
During the storm, not enough sunlight reached the rover’s solar panels, so Opportunity slipped into low-power mode, with just enough power to run the rover’s internal clock, until its batteries could charge again. Only that didn’t happen and the rover’s internal clock may have stopped keeping accurate time. This meant that Opportunity was burning through its battery instead of going into sleep mode at night.
“With a loss of power, the clock on the rover gets scrambled, and it wouldn’t know when to deep sleep, so it probably wasn’t sleeping at night when it needed to,” Callas explained during the briefing. “And that heater was stuck on, draining away whatever energy the solar arrays were accumulating from the sun to charge those batteries.”
Opportunity’s retirement does not mean we’re nearing the end of Martian science or Mars rovers. It’s nuclear-powered counterpart, Curiosity, is still sciencing the shit out of Mars and taking epic selfies as it goes along. The InSight lander has unpacked its instruments and will soon begin science operations. And they won’t be alone for long. NASA’s next rover, dubbed Mars 2020, is expected to land on the red planet in early 2021, followed by a European rover later that same year.
Opportunity’s final words to us (back in June) were as poetic as they were bittersweet: “My battery is low and it’s getting dark.” Rest easy little rover, you met an honorable end—one that came a whole lot later than any of us ever expected.