NASA on Tuesday announced it was extending for the fifth time the mission of Mars space probes Spirit and Opportunity, in their indefatigable exploration of the Red planet.
The two robots touched down three weeks apart on Mars in January 2004 for an expected 90-day mission that instead could stretch out to 2009, the National Aeronautics and Space Administration said on its website.
In September, Opportunity began a perilous descent into the Victoria crater, in Mars' Meridiani Planum region.
On the opposite side of the dusty planet and in opposite direction, Spirit in early September began climbing onto the Home Plate volcanic plateau where scientists believe the volcanic rock might contain traces of water.
"After more than three-and-a-half years, Spirit and Opportunity are showing some signs of aging, but they are in good health and capable of conducting great science," said John Callas, rover project manager at NASA's Jet Propulsion Laboratory, Pasadena, California.
The roving probes carry several sophisticated instruments to examine the geology of Mars for information about past environmental conditions.
Opportunity has returned dramatic evidence that its area of Mars stayed wet for an extended period of time long ago, with conditions that could have been suitable for sustaining microbial life, NASA said.
Spirit has found evidence in the region it is exploring that water in some form has altered the mineral composition of some soils and rocks, the space agency added.
To date, Spirit has driven 7.26 kilometers (4.51 miles) and has sent back to Earth more than 102,000 images. Opportunity has driven 11.57 kilometers (7.19 miles) and has returned more than 94,000 images.