NASA scientists said today they have lost contact with the robot rover Spiriton Mars and were unsure what had caused the problem.
Mission controllers say they last heard from the probe early yesterday. Since then, it has returned just random, meaningless data - and only then sporadically.
Initially, the scientists said they believed weather problems on Earth caused the glitch.
They now said they believe the rover was experiencing hardware or software problems.
"This is a serious problem. This is an extremely serious anomaly," project manager Mr Pete Theisinger said.
Spiritis one half of a €650 million mission. It landed on Mars on January 3rd on a planned three month mission to explore the geologic history of the planet. Its twin, Opportunity, is scheduled to land on Mars on Saturday.
NASA last heard from Spiritas it prepared to continue its work examining its first rock, just a few yards from its lander. Since then, Spirithas transmitted just a few beeps to Earth in response to attempts to communicate with it.
It has also skipped several scheduled communications opportunities, either directly with Earth or by way of two NASA satellites in orbit around Mars. Engineers at NASA's Jet Propulsion Laboratory are working to pinpoint the yet-unknown problem.