It’s been a long time coming, but this week NASA’s Mars Opportunity rover completed the first-ever Martian marathon. After landing on the Red Planet in January 2004 on a mission originally planned to only last 90 days, Opportunity has instead endured for more than a decade, and has taken eleven years and two months to travel the marathon-standard 42.195 kilometers. On average, that’s only about ten meters per day—slower even than a snail’s pace.

“This is the first time any human enterprise has exceeded the distance of a marathon on the surface of another world,” says John Callas, Opportunity’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California. “A first time happens only once.”

The Opportunity team at JPL is planning a marathon-length relay run next week to celebrate the milestone.

“This 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,” said Steve Squyres, Opportunity’s principal investigator at Cornell University in Ithaca, New York. “Still, running a marathon on Mars feels pretty cool.”

Opportunity broke off-world distance records last year when it surpassed the 39-kilometer lunar traverse made by the Soviet Union’s Lunokhod 2 rover in 1973. Its sister rover, Spirit, which landed on the Red Planet two weeks before Opportunity, managed to trundle 7.7 kilometers before being mired in soft sand and finally succumbing to the harsh Martian winter in 2010.

During its long journey, Opportunity has found a wealth of evidence suggesting that Mars was once a much wetter, warmer place, with ancient lakes that could have been favorable environments for microbial life. The rover’s marathon has taken it to the edge of Endeavour Crater, and the science team now hopes to send the rover into “Marathon Valley,” a region of the crater rim with steep, clay-rich slopes. Studying the clay layers in the slope could reveal even more about the planet’s past and present habitability, and Mars-focused researchers are eagerly awaiting Opportunity’s next phase.

But all is not well with the Opportunity’s support back on Earth, and the mission’s next phase may be cut short. Opportunity costs about $14 million per year to operate, but that funding is in jeopardy. NASA’s newer, bigger, nuclear-powered Curiosity rover is the only other spacecraft presently on Mars, and takes up the lion’s share of resources for ongoing surface operations. NASA’s proposed budget for 2016 includes no money at all for operating Opportunity, despite an agency Senior Review panel ranking Opportunity’s proposed science plan the highest out of all current Mars missions.

Final funding levels will be set when Congress modifies the proposed budget before passing it, but Opportunity will still face long odds.

The agency’s administrator, Charles Bolden, has made it plain the mission’s days are numbered. Testifying before the Senate earlier this month, Bolden called Opportunity a mission “whose time has passed.” Continuing it, he said, would hinder NASA’s ability to pursue new, more ambitious science missions to Mars. Congress may modify NASA’s proposed budget before passing it, but with its marathon behind it, Opportunity’s roving days seem almost at an end.