(CNN) - It's time to say goodbye to Opportunity. The Mars rover's team made its last attempt to contact Opportunity on Tuesday night, and it went unanswered. On Wednesday, NASA confirmed that the mission is over.
"For more than a decade, Opportunity has been an icon in the field of planetary exploration, teaching us about Mars' ancient past as a wet, potentially habitable planet and revealing uncharted Martian landscapes," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate. "Whatever loss we feel now must be tempered with the knowledge that the legacy of Opportunity continues, both on the surface of Mars with the Curiosity rover and InSight lander and in the clean rooms of [NASA's Jet Propulsion Laboratory], where the upcoming Mars 2020 rover is taking shape."
Solar-powered Opportunity hasn't communicated with engineers since June 10. Dust has blocked out sunlight, and even the expected winds from November through January haven't helped clear Opportunity's sensors and panels. Engineers tried different things to revive Opportunity, sending repeated signals and commands to attempt to fix other potential issues. They've sent more than 835 recovery commands that remain unanswered.
"We have made every reasonable engineering effort to try to recover Opportunity and have determined that the likelihood of receiving a signal is far too low to continue recovery efforts," said John Callas, manager of the Mars Exploration Rover project at NASA's Jet Propulsion Laboratory.
The team is grateful for the long mission but sad to say goodbye. "Science is an emotional affair. It's a team sport, and that's what we're celebrating today," Zurbuchen said.
When Opportunity's twin, Spirit, became mired in soft soil in 2009 and its five working wheels couldn't free the rover, NASA held a "service" to commemorate the end of the mission in May 2011.
"Oppy," as the rover is affectionately known, has well outlasted her original 90-day mission. Instead, the rover has persisted for 15 years, sending back incredible data and photos from Mars to help uncover the Red Planet's secrets.
Opportunity and Spirit launched in 2003 and landed on Mars in 2004, searching for signs of ancient life.
Opportunity found hematite at its landing site: little round things all over the ground that looked like blueberries. These features form in water, a definitive sign to NASA that liquid water had been on the surface of Mars.
Opportunity was expected to travel 1,100 yards over 90 days on Mars. Instead, it traveled 28 miles.
It landed in Eagle Crater, moved on to Endurance Crater and planned to visit Victoria Crater. But the rover got stuck in the dunes of windblown material on the Martian surface. The engineers put it in reverse and "gunned it" to free the rover.
Opportunity was able to visit Victoria and spend two years driving around it and inside it before moving on to Endeavour Crater and ending in Perseverance Valley.
Opportunity's mission has led to many discoveries about the Red Planet, but perhaps the most exciting was when the rover found evidence that Mars once had water and supported conditions for sustaining microbial life.
"From the get-go, Opportunity delivered on our search for evidence regarding water," said Steve Squyres, principal investigator of the rovers' science payload at Cornell University. "And when you combine the discoveries of Opportunity and Spirit, they showed us that ancient Mars was a very different place from Mars today, which is a cold, dry, desolate world. But if you look to its ancient past, you find compelling evidence for liquid water below the surface and liquid water at the surface."
Opportunity not only leaves behind a legacy of discovery, it became the longest-running rover and captured 217,594 raw images.
It will probably stay where it fell silent in Perseverance Valley. There, a historic global dust storm blackened the skies and starved its batteries of energy. The team listened for the rover every day, worrying as the skies continued to darken and the temperatures dropped. But the historic storm proved to be too much for Opportunity.
"I cannot think of a more appropriate place for Opportunity to endure on the surface of Mars than one called Perseverance Valley," said Michael Watkins, director of JPL. "The records, discoveries and sheer tenacity of this intrepid little rover is testament to the ingenuity, dedication and perseverance of the people who built and guided her."
This is the last image the panoramic camera captured before the rover communicated to engineers that its power was running low and that the dusty conditions were making things quite dark.
But Opportunity had shown other signs of age. It had a heater that was draining energy, and the clock was scrambled by loss of power, so it didn't know when to sleep. Then, the flash memory stopped, so the team had to recover the rover's data every day before it "forgot" what it saw.
Meanwhile, the Curiosity rover, which was unaffected by the storm, and the stationary InSight lander continue to study the Red Planet and carry on missions of discovery that were founded by Opportunity and Spirit.
Curiosity tweeted its farewell to Opportunity.
On Tuesday, InSight deployed its "mole," or heat flow probe, on the Martian surface, and in the coming weeks, it will be the first probe to go more than 16 feet below the surface. This will determine Mars' subsurface temperature and thermal conductivity.
InSight also shared a fond farewell to Opportunity on Twitter.
On Wednesday, Opportunity's team bid her farewell while looking to the foundations the mission laid.
"When I think of Opportunity, I will recall that place on Mars where our intrepid rover far exceeded everyone's expectations," Callas said. "But what I suppose I'll cherish most is the impact Opportunity had on us here on Earth. It's the accomplished exploration and phenomenal discoveries. It's the generation of young scientists and engineers who became space explorers with this mission. It's the public that followed along with our every step. And it's the technical legacy of the Mars Exploration Rovers, which is carried aboard Curiosity and the upcoming Mars 2020 mission.
"Farewell, Opportunity, and well done."
And one day, NASA hopes rover tracks will be alongside human footprints on the Red Planet.
"It is because of trailblazing missions such as Opportunity that there will come a day when our brave astronauts walk on the surface of Mars," NASA Administrator Jim Bridenstine said. "And when that day arrives, some portion of that first footprint will be owned by the men and women of Opportunity and a little rover that defied the odds and did so much in the name of exploration."
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