Nasa is celebrating the fifth year of operation for its two Mars rovers. The original plan anticipated that Spirit and Opportunity would be operational for 90 days, but the machines are still in operation nearly five years later.
Over that time they have covered 21 kilometres of the Martian surface and relayed 36GB of data back to Earth.
"The American taxpayer was told that three months for each rover was the prime mission plan," said Ed Weiler, associate administrator for Nasa's Science Mission Directorate at Nasa headquarters in Washington.
"The twins have worked almost 20 times that long. That's an extraordinary return on investment in these challenging budgetary times."
The two solar powered rovers were designed to traverse the Martian landscape for just one season. However, their solar charging capability was underestimated, since Martian storms have cleared dust from the panels allowing them to operate more efficiently.
Nevertheless, there have been problems. One wheel on the Spirit rover jammed in 2007 and its power levels are now very low.
"This last winter was a squeaker for Spirit. We just made it through," said John Callas, project manager for Spirit and Opportunity at Nasa's Jet Propulsion Laboratory.
"We realise that a major rover component on either vehicle could fail at any time and end a mission with no advance notice, but on the other hand we could accomplish the equivalent duration of four more prime missions on each rover in the year ahead."
US utility announces power supply deal that could see it buy power generated by solar satellites within seven years 17 Apr 2009
Secretary-General and climate envoy cross swords over the extent to which UN talks should be supported by separate negotiations between top polluters 18 Mar 2010
As a journalist, I spend a fair amount of time defending the much maligned media industry to friends and family.... 18 Mar 2010
Andrew Williams casts his eye over some of the most popular green driving aids on the market 16 Mar 2010
From hydropower hot spots to record-breaking Texan winds, we run down the top stories from the past week 12 Mar 2010









