LOS ANGELES, Oct. 15 (Xinhua) -- The missions of Mars rovers Spirit and Opportunity managed by the Los Angeles-based Jet Propulsion Laboratory (JPL) will be extended again, it was announced on Monday.

The extension means the rovers will continue operating on opposite sides of Mars possibly through 2009, the National Aeronautics Space Administration (NASA) said.

This is the fifth time scientists have extended the mission for the rovers which have long passed their expected lifetimes.

The rovers were only expected to explore the red planet for 90 days when they first traveled the 303 million miles (about 485 million km) to Mars in 2004. They are now on their 45th month of operation.

"We are extremely happy to be able to further the exploration of Mars. The rovers are amazing machines, and they continue to produce amazing results operating far beyond their design life," said Alan Stern, associate administrator for NASA's Science Mission Directorate in Washington.

The rovers explore the planet's surface and transmit scientific data back to scientists on Earth.

"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 the JPL.

The rovers carry sophisticated instruments to examine the geology of Mars in hopes of giving scientists information about the planet's environmental past.

In September, Opportunity began descending into the largest crater it has visited -- the approximately half-mile-wide and 230-foot-deep Victoria Crater in Mars' Meridiani Planum region.

Meanwhile, Spirit climbed a volcanic plateau in a range of hills far from its landing site.

During the 45-month exploration, Spirit has driven 4.51 miles (about 7.6 km) and returned more than 102,000 images.

Opportunity has driven 7.19 miles (about 11.6 km) and returned more than 94,000 images.

The rovers have run into trouble during their 45-month adventure. Most notably, they were nearly destroyed in a severe dust storm this summer.

Spirit lost the use of one of its wheels more than a year ago, limiting its ability to climb on the Martian surface.