The Energizer bunny has some serious competition when it comes to things that just won't quit. I'm talking about NASA's Opportunity Mars rover, which successfully finished traveling the equivalent of an Olympic marathon, covering a stunning 26.219 miles (about 42 km) as of Tuesday.

And while there was no finish line or streamers for the 11-year-old rover, NASA still had its own small celebration back on Earth.

"This is the first time any human enterprise has exceeded the distance of a marathon on the surface of another world," John Callas, the Opportunity project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., recently announced.

"A first time happens only once," he added with pride.

The Opportunity team has even planned a fitting celebration to mark the momentous occasion next week, by holding a marathon-length relay race with staff, family, friends, and supporters.

Meanwhile, Opportunity, which has outlived its sister-rover Spirit by about five years, will just keep trucking. And while 26 miles in 11 years certainly doesn't seem like a lot, Steve Squyres, Opportunity's principal investigator at Cornell University, remind us that the rover's mission "isn't about setting distance records, of course; it's about making scientific discoveries on Mars and inspiring future explorers to achieve even more." (Scroll to read on...)

Traveling at a max speed of five centimeters (~2 inches) per second - with an average traveling speed that's about a fifth of that - Opportunity is no offroading speedster. Instead, the 440-pound Mars rover was intended to look specifically for signs of water activity in the Red Planet's past and assess whether the planet was ever once habitable for life.

Touching down on Martian soil in 2012, NASA's Curiosity Rover officialy took over this primary mission, allowing Opportunity to turn its attention to things like... say... completing a marathon! Not many retirees on Earth can say they've attempted the same.

And while the rover has even now finished that goal, it hasn't stopped moving. Opportunity has now lasted more than 40 times its estimated functional time, leaving people like Squyres scrabbling to dream up its next big goal.

"Still," the scientist added, it's not like this extra work isn't worth it. After all, earning bragging rights for "running a marathon on Mars feels pretty cool."

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