Eight months after losing contact with theduring a record dust storm, NASA managers Wednesday reluctantly called it quits, officially bringing one of the agency's most successful projects to an end after an improbable 15-year mission that captured the imaginations of millions.
The decision to halt efforts to contact the long-lived rover came after last-ditch attempts failed to detect any sort of response from the six-wheeled robot.
"I was there with the team as these commands went out into the deep sky, and I learned this morning that we had not heard back and Opportunity remained silent," said Thomas Zurbuchen, NASA associate administrator for space science. "It is therefore that I'm standing here with a sense of deep appreciation and gratitude that I declare the Opportunity mission as complete."
Standing in a packed auditorium at the Jet Propulsion Laboratory in California, addressing the men and women who built and operated Opportunity, Zurbuchen said, "I have to tell you, it's an emotional time."
"Science is an emotional affair, it's a team sport, and that's what we're celebrating today," he said. "I will never forget the amazing work that happened here. It transformed our understanding of our planet. Everything we do and think about in our planetary neighborhood with Mars and elsewhere relates to the research that came from that, and the engineering breakthroughs that came from that."
Opportunity was designed to operate for just 90 days on the martian surface but far outlived even the most ardent supporter's wildest expectations, roving 28 miles across the surface of Mars for more than 14 years.
Opportunity and its twin rover, Spirit, conclusively showed that Mars once enjoyed a warmer, wetter environment with flowing water at the surface -- an environment researchers now know was habitable in the distant past.
Spirit ended operations in 2010 after getting stuck in sand drifts, but Opportunity kept going.
Then last June, a thick dust storm clouded the martian atmosphere, sharply reducing the sunlight reaching the rover's solar panels. Without electricity from the solar cells, the spacecraft's batteries could not recharge and power levels presumably fell below the minimum needed to keep the rover's computer and its master clock operating.
Global dust storms are not unusual on Mars, occurring every few years. In fact, Opportunity weathered a major dust storm in 2006 with no problem. But this time, the storm was worse and the opacity of the atmosphere climbed to unprecedented levels. NASA lost contact on June 10.
"We tried valiantly over these last eight months to try to recover the rover, to get some signal from it. We listened every single day with the Deep Space Network, and we sent over a thousand recovery commands, trying to exercise every possibility of getting a signal from the rover," said John Callas, the project manager at JPL.
As time passed and the martian winter approached, with darker skies and lower temperatures, hope started to fade. The team held out hope that the windy season on Mars might blow accumulated dust from the arrays and permit battery charging, but after a final round of commands Tuesday night, "we heard nothing," Callas said.
"And so, it comes time to say goodbye," he said. "But we want to remember the 14-and-a-half years of phenomenal exploration. This was a 90-day mission, and we were so excited by just having three months to explore the planet with just a kilometer of capability. But 14-and-a-half years later, and 45 kilometers of odometry, we've done phenomenal things. We've greatly expanded our understanding of the red planet."
Opportunity was surrounded by protective airbags when it bounced to a touchdown on Mars in January 2004, landing on Meridiani planum, half a world away from Gusev Crater where its twin rover — Spirit — landed three weeks earlier.
With Spirit and Opportunity now out of action, NASA is left with five spacecraft on or around Mars. Three of those are in orbit around the planet.
NASA also operates two spacecraft on the surface of the red planet: the nuclear-powered Mars Curiosity rover, now in its seventh year of operation, and the stationary InSight lander, which touched down late last year. The space agency is developing another Curiosity-class rover for launch in 2020.