Today NASA closed the chapter on the Mars rover Opportunity — fondly referred to as Oppy — after eight months of silence. Designed to operate for 90 days on the surface of Mars, Oppy lasted for more than 14 years before succumbing to an historic dust storm that prevented the Sun from recharging its batteries. Oppy’s twin, Spirit, ceased functioning in 2011. Now only two spacecraft are operating on the Martian surface: NASA’s Curiosity rover and InSight lander.

Spirit and Opportunity comprised the Mars Exploration Rover (MER) program. The spacecraft were designed and operated by the Jet Propulsion Laboratory (JPL) in Pasadena, CA. At a media briefing there today, Thomas Zurbuchen, head of NASA’s Science Mission Directorate, declared Opportunity and the MER program “complete.”

Though the probes are robotic, they were designed, built, and operated, and their data studied by, humans. The end is an emotional experience for many. John Callas, MER project manager, said that sitting in mission control over long nights watching the rovers’ vital signs makes them seem like children. Saying goodbye is “very hard and very poignant.”

Opportunity landed on Mars on January 24, 2004. Its last contact with Earth was on June 10, 2018 as a dust storm enveloped Mars. The rover uses solar panels to recharge its batteries and the dust prevented sufficient sunlight from reaching the panels. With no battery power, the rover had no heat to keep the instruments and other systems warm.

NASA and the Mars science community held out hope that the plucky rover could hold on until the dust cleared. NASA sent more than 835 commands to Oppy over the past eight months hoping for a reply. Last night was the final attempt. There was no response. Callas said the likelihood of receiving a signal now is “far too low” to keep trying.

NASA communicates with spacecraft beyond Earth orbit through its Deep Space Network (DSN) of antennas in California, Spain and Australia. The DSN has finite capacity and many users — from spacecraft close to the Sun (Parker Solar Probe) to the edge of the solar system (New Horizons, Voyager 1 and 2) and many places in between, including Mars. In addition to NASA’s Curiosity and InSight on the surface of Mars (which are nuclear-powered and not affected by dust storms), six operational spacecraft are orbiting the Red Planet: NASA’s Mars Odyssey, Mars Reconnaissance Orbiter, and MAVEN; ESA’s Mars Express and ExoMars Trace Gas Orbiter; and India’s Mars Orbiting Mission.

Today was a day to celebrate Opportunity and the human team behind its more than 14 years of scientific discovery. JPL provided a video looking back on the mission and a list of six key achievements.

Set a one-day Mars driving record March 20, 2005, when it traveled 721 feet (220 meters).

Returned more than 217,000 images, including 15 360-degree color panoramas.

Exposed the surfaces of 52 rocks to reveal fresh mineral surfaces for analysis and cleared 72 additional targets with a brush to prepare them for inspection with spectrometers and a microscopic imager.

Found hematite, a mineral that forms in water, at its landing site.

Discovered strong indications at Endeavour Crater of the action of ancient water similar to the drinkable water of a pond or lake on Earth.

The search for liquid water is at the heart of NASA’s Mars exploration strategy. Life as we know it requires liquid water and NASA wants to determine if the Mars ever could have supported life.

MER’s principal investigator, Cornell University’s Steve Squyres, said that “[f]rom the get-go, Opportunity delivered on our search for evidence regarding water.” Looking at all of the data from both MER rovers, “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 into its ancient past, you find compelling evidence for liquid water below the surface and liquid water at the surface.”

Presidents George H.W. Bush, George W. Bush, Barack Obama, and Donald Trump all established policies directing NASA to pursue plans to send humans to Mars. Today, others, like SpaceX’s Elon Musk, also have that goal. Knowing if water is accessible to support humans there is important to those plans as well.

NASA Administrator Jim Bridenstine offered this view of Opportunity’s legacy.

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. 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. — Jim Bridenstine

Opportunity sent back more than 200,000 images, but perhaps none so compelling to the public as those showing its own shadow on the surface of the Red Planet.