NASA scientists say they have lost contact with the robot rover Spirit on Mars and are unsure what caused the problem.

Spirit project manager Pete Theisinger told a news briefing that there was a "very serious anomaly" in communications with the six-wheeled craft, which landed on Mars on January 3 on a planned three-month mission to explore the geologic history of the planet. Theisinger said on Thursday scientists had been unable to communicate with Spirit for about 24 hours and had so far been unable to explain the source of the problem.

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