NASA scientists this week celebrated the fact their robot buddy Opportunity has spent the past fifteen years on Mars.

The six-wheeled bot was booted into space on July 7, 2003, and reached its final destination in less than a year, on January 24, 2004. A day later, it beamed its first signal back to Earth.

Designed to operate for 90 Martian days, and cover just over 1,000 metres on Mars, Opportunity has exceeded expectations, trundling at least 45 kilometres (28 miles) for more than a decade.

Sorry, but NASA says Mars signal wasn't Opportunity knocking READ MORE

Although it’s an achievement, the rover hasn’t really been fully operational during its 15-year stretch on the Red Planet. In fact, NASA boffins haven’t heard a peep from it since a giant dust storm hit Mars, and covered the poor robot’s solar panels, in June last year.

“This anniversary cannot help but be a little bittersweet as at present we don't know the rover's status. We are doing everything in our power to communicate with Opportunity, but as time goes on, the probability of a successful contact with the rover continues to diminish," said John Callas, NASA’s project manager for Opportunity.

The mission isn’t quite over yet, however. Engineers are still sending commands to Opportunity, hoping for a reply. The American space agency said if it hears anything back, its eggheads will attempt to regain control of the sleeping bot.

Opportunity was sent to Mars to uncover the mysteries of its past, and has helped scientists confirm suspicions that the planet was not as dry as previously thought. It found hematite, a mineral that requires water to form, in rocks littered on the Meridiani Planum, an area located south of the Martian equator.

Even if the geologist robot is in hibernation, it still remains the longest-running rover on Mars. It has outlived its twin companion, Spirit, who landed earlier on the 3 January but broke down after its wheel got stuck in soft soil.

This meant that the rover couldn’t orient its solar panels correctly and the rover ran out of juice in 2010. Not all is not lost, however, NASA’s nuclear-powered Curiosity rover is still chugging along, sniffing about for signs of microbial life, and should soon be joined by Curiosity 2.0, hopefully in the next couple of years. ®