WASHINGTON — NASA announced Feb. 13 that it was ending efforts to restore contact with the Opportunity Mars rover, bringing its mission to an end more than 15 years after it landed on the planet.

At an event at the Jet Propulsion Laboratory, project officials and NASA leadership said they were declaring the overall Mars Exploration Rovers project over after months of attempts by spacecraft controllers failed to reestablish communications with Opportunity after a major dust storm cut off power to the rover in June.

“I am standing here, with a sense of deep appreciation and gratitude, to declare the Opportunity mission as complete, and with it the Mars Exploration Rovers mission as complete,” said Thomas Zurbuchen, NASA associate administrator for science. That decision came after Opportunity failed to respond to a final set of commands transmitted to it by the Deep Space Network Feb. 12.

Opportunity last contacted Earth in early June as “an historic” global dust storm reached its location on Mars, said John Callas, project manager for the Mars Exploration Rovers at JPL. That storm darkened the skies and cut off of the rover’s solar power.

“We tried valiantly over these last eight months to try to recover the rover, to get some signal from it,” he said. However, the onset of winter at the rover’s location on Mars, a region called Perseverance Valley, meant less sunlight and colder temperatures, making it increasingly unlikely the rover could be recovered.

“It brought us to last night, and we sent our final commands, and we heard nothing,” he said. “So, it comes time to say goodbye.”

Opportunity was the second of the twin Mars Exploration Rovers to land on Mars, arriving in January 2004 about three weeks after Spirit landed. The rovers had 90-day lifetimes, but each far exceeded that. Spirit’s mission ended in May 2011 after traveling eight kilometers, while Opportunity logged 45 kilometers before losing contact last June.

Callas said the extreme longevity of the rovers could be credited in part to winds that cleared dust that had accumulated on the solar panels that, if not removed, would have diminished the power those panels generate. The rovers’ batteries also exceeded expectations, retaining 85 percent of their original capacity after more than 5,000 charge/discharge cycles.

A glitch with Opportunity that dates back to very early in its mission may have contributed to its demise. Callas said a heater in the rover’s robotic arm got stuck on shortly after landing, depleting the rover’s batteries during the night. “If we left it alone like that, the mission wouldn’t have lasted long beyond the 90 days,” he said.

To correct the problem, engineers developed a “deep sleep” mode to turn off all the heaters each night. When the dust storm hit, the loss of power “scrambled” Opportunity’s internal clock, keeping it from engaging that deep sleep mode each night. “It probably wasn’t sleeping at night when it needed to, and that heater was stuck on, draining away whatever energy the solar arrays were accumulating from the sun,” he said.

The JPL event was billed as a media briefing but was more of a celebration of the rover, with project scientists and engineers reminiscing about the mission. Only a few minutes at the end of the hour-long event was devoted to media questions.

Steve Squyres, the Cornell University planetary scientist who was principal investigator for the Mars Exploration Rovers, divided Opportunity’s mission into two parts. The first, lasting about nine years, covered initial exploration of its landing site, turning up evidence of water, albeit rather acidic, early in the planet’s history.

The project then made the decision to make a long trek to a distant crater, Endeavour. “When we got there the mission started all over again,” he said. That included finding evidence of past water on Mars that had a neutral pH, rather than acidic. “That was one of the mission’s most significant discoveries. It came 11 years into our 90-day mission.”

Asked later in the briefing whether either of the Mars Exploration Rovers might one day be retrieved to place in a museum, Squyres noted that huts from the early exploration of Antarctica, more than a century ago, have been preserved there. The same, he suggested, should be the case for the rovers. “We built them for Mars. That’s the place they were designed to go. That’s their home. That’s where I would like them to stay,” he said.

Another opinion, though, came from Ellen Stofan, a planetary geologist and director of the National Air and Space Museum. Speaking at the Commercial Space Transportation Conference here Feb. 13, shortly after the JPL event, she discussed ongoing renovations of the museum and plans for new exhibits.

“What I’m looking forward to in the museum, the artifact that I most want, is something from one of the Mars rovers that one of the first crews on Mars has been able to bring back to Earth,” she said. “I’ll put that right next to my Mars rock.”