The twin Mars rovers are getting wiser with age. Engineers have transmitted new flight software to the rovers' onboard computers, just in time for the third anniversary of their landings. The software is aimed at boosting their intelligence and independence so that they can roll around the Red Planet with less help from humans.

"We're teaching an old dog new tricks," said John Callas, the mission project manager with the Jet Propulsion Laboratory, the NASA agency in charge of the rovers.

Among the rovers' new skills is the ability to automatically recognize and transmit to Earth photographs that they take of swirling dust devils or floating clouds. They can also independently decide whether it is safe to extend their robotic arms to sample rocks.

Advancement savestime for scientists

Before, scientists had to painstakingly dissect thousands of images just to find the frames they needed anddecide for the rovers whether to use their arms. The high-tech upgrades should help save timebecause scientists on Earth don't have to study a rock before sending commands to the robot to use science instruments on it.

If successful, the changes could get incorporated into future Mars missions.

Spirit and Opportunity were also fitted with a new navigation system that allows them to think several steps ahead when faced with an obstacle, allowing them to back out of a dead end or even navigate a maze on their own, Callas said. The robot geologists had previously tackled one problem at a time.

Spirit landed three years ago Wednesday and Opportunity on Jan. 24, 2004. Entering their fourth year of exploration, both golf cart-sized vehicles have long outlasted their primary missions, originally planned for about three months.

The rovers' biggest accomplishment is uncovering geologic evidence that water once flowed on Mars. Spirit is currently studying rocks and soil samples near a Martian ridge while Opportunity is circling the rim of a massive crater for possible ways into it.