In what must rate as the single greatest achievement in the history of space exploration, the Opportunity rover celebrates 2 years of activity on the Martian surface today. The mission was expected to last no more than 90 days, but thanks to some fantastic engineering and a little luck (high winds are believed to have swept clear it's dust covered solar panels), the pluckly little rover just keeps on going. Over 7 miles have been traversed and 58,000 images returned so far, along with conclusive proof that Mars was once a very wet place. Opportunity's sister rover Spirit is due to pass it's own two year milestone in a few days. Undoubtedly both are on borrowed time, but the lure of the next rise always beckons, and those of us with Mars in our blood still cling to the hope that a lost Martian city may yet rise from the sands. Good luck Opportunity and Spirit, and congratulations to the teams responsible for this incredible mission. Long may they continue to rove the surface of Mars.