Winds fail to revive NASA's Opportunity rover - Science Magazine

NASA’s Opportunity rover, seen here in a composite image, landed on Mars 15 years ago. Its end is nigh.

Mars Exploration Rover Mission/Cornell/JPL/NASA

By Paul VoosenJan. 25, 2019 , 5:05 PM

There’s little hope left for rousing NASA’s Opportunity rover, which landed on Mars 15 years ago this month. For the past 6 months, the rover has sat silently and NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, is running out of tricks to revive it. In the next few weeks, officials at the agency’s headquarters will decide whether to continue the search, the mission’s scientists say.

In June 2018, a planet-encircling dust storm blotted out the sun over Opportunity for several months, weaning it off solar power and draining its batteries. Since then, JPL has sent the golf cart–size rover 600 commands to revive it. Engineers hoped seasonal winds, running high between November 2018 and the end of January, would clear the solar panels of dust, allowing for its recovery. But that hasn’t happened.

“The end of the windy season could spell the end of the rover,” says Steven Squyres, the mission’s principal investigator at Cornell University. “But if this is the end, I can't imagine a better way for it to happen … 15 years into a 90-day mission and taken out by one of the worst martian dust storms in many years.”

John Callas, the misson project manager at JPL, says, “We’ve got another week. We’re running out of time.”

The martian winter, which in 2011 ended the mission of Opportunity’s twin rover, Spirit, is months away. Sunlight is waning in the southern hemisphere and temperatures are dropping. Efforts to revive the rover have now lasted as long as the past campaign to revive Spirit. JPL is trying a few more long shots, such as commands that would tell Opportunity to switch to back antennas, if it had barely revived and was trying to use a broken antenna. “After that, I don’t know what to do next, if anything,” Callas says. Before the 5-week U.S. government shutdown, the plan was to have NASA headquarters weigh in on whether to continue the efforts after the windy season, he adds. With a plan now in place to reopen the government, such a decision could come soon from NASA science chief Thomas Zurbuchen.

Whenever its mission ends, Opportunity will leave a trail of superlatives. Although it was only guaranteed to last 90 days on Mars, it ended up enduring at least 5000. It traversed a path 45 kilometers long, often driving backward because of an overheating steering control. It explored ever-larger impact craters as it went, with their deposits revealing more and more of the martian interior. Even after all that time, its 1-megapixel cameras were still working beautifully, says Jim Bell, a planetary scientist at Arizona State University in Tempe who leads the rover’s color camera team. Bell, for one, isn’t giving up hope. The rover is perched on the rim of Endeavor crater, he notes, and a wind gust could still come and revive Opportunity. “No one has ever won a bet against it. I’m not about to start.”

From its landing in Meridiani Planum in 2004, Opportunity quickly revealed the sulfate-rich sandstones it drove on. The stones likely formed as shallow muds in lagoonlike environments, says Raymond Arvidson, a planetary scientist at Washington University in St. Louis, Missouri, and the rover’s deputy principal investigator. “There was an ephemeral lake system, going dry, going wet. That’s a huge discovery.” The rover was intended to explore where Mars could have been habitable in the deep past, Bell adds, and Opportunity was the first to provide possible evidence for it.

Subsequent craters explored by the rover revealed that periods of habitability extended far longer in the martian past than once thought. It spotted veins of the mineral gypsum near crater rims, which form thanks to evaporating water. And, in 2013, it provided the first surface observations of 4-billion-year-old clays, from a time on Mars older than the rocks probed by the Curiosity rover, when water could have truly been abundant. The finding, 9 years into its mission, validated observations from orbit, expanding the hunt for such clays, says Alberto Fairén, a planetary scientist at Cornell. “A beautiful example of how collaborative science should be done.”

Few expected when they signed up for the Spirit and Opportunity rovers that they’d still be working on one 15 years later. In the end, though, Bell adds, “Mars always wins.”

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