LOS ANGELES -- NASA is ending attempts to regain contact with the long-lived Mars exploration rover Spirit, NASA's Jet Propulsion Laboratory (JPL) announced Tuesday.

According to the JPL, engineers' assessments in recent months have shown a very low probability of recovering communications with Spirit.

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"We no longer believe there is a realistic probability of hearing from Spirit," the JPL said, adding that it would make one last attempt on Wednesday.

NASA said that with inadequate energy to run its survival heaters, critical components on the rover probably failed from extremely cold temperature during the past Mars winter, because the internal temperature was colder last year than in any of its prior six years on Mars.

The rover's motors worked far beyond their design life. It lost use of drive motors on two of its six wheels eventually, leaving it unable to obtain a favorable tilt for solar energy during the fourth Martian winter, which began last May.

NASA is currently preparing for the launch of another Mars rover. "We're now transitioning assets to support the November launch of our next generation Mars rover, Curiosity," said Dave Lavery, NASA's program executive for solar system exploration.

Spirit landed on Mars on January 3, 2004, for a mission designed to last three months. It has made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life.