NASA is saying farewell to its Mars Opportunity rover after being out of communication with the robot explorer for about a year. This will mark the end of a nearly 15-year mission on the Martian surface. Goodbyes were sent on Twitter from engineers working at NASA's Jet Propulsion Laboratory, but a formal announcement by NASA was just made today.Jet Propulsion Laboratory engineers sent the final official transmission to the rover last night, but communications from the rover back to NASA ended last June. The reason was a massive dust storm that blotted out the sky. Opportunity runs on solar power, so this was a death sentence for the little rover. This storm in particular was one of the thickest NASA has ever seen. Once it had passed, engineers were hopeful that the sun would wake Opportunity up again. It had gone into hibernation mode as the internal battery slowly drained away. However, the radio silence continued.The dust storm likely left a layer of dirt and silt on Opportunity's solar panels. NASA had hoped wind would clear them off, but the windy months are now behind us, and there's still no sign of life. Opportunity will enter Martian winter soon, which could bring temperatures down below -150 degrees Fahrenheit. Opportunity has survived a lot of previous winters on Mars, but NASA says that without power for the internal heaters, components could become brittle and break.Opportunity lasted far beyond what anyone thought it could withstand. When it and its identical twin Spirit landed in January 2004, NASA expected them to last 90 Martian days. Instead, Opportunity lived for nearly 15 years. (Spirit got stuck in a sand trap and went dark in 2009, still far beyond its intended expiration date.) They were designed to travel 1,100 yards. Instead, Opportunity traveled more than 28 miles, and Spirit almost 5. Over the years Opportunity and its team of engineers on Earth overcame several near-fatal challenges: lost steering to one front wheel and then the other, a two-month dust storm that threatened to do it in, getting mired in sand, a stuck heater and the loss of its flash memory. But it endured to become the most traveled and longest-lasting rover ever to explore another planet.NASA held a press conference today chronicling its life and going into even further detail on why Opportunity is officially being let go. You can watch the stream below.

"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," said NASA Administrator Jim Bridenstine. "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."



NASA/JPL listed just a few of Opportunity's accomplishments — not the least of which was the body of evidence it amassed proving that Mars, though now barren, was once a much more watery place:

Set a one-day Mars driving record on March 20, 2005, when it traveled 721 feet.

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.

"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 JPL, where the upcoming Mars 2020 rover is taking shape."