NASA's Mars Spirit Rover has overcome the memory glitch and would be rolling again this weekend. However, the scientists are still trying to find out what caused memory loss in Mars.

On its 1800th day on Mars, rover Spirit failed to carry out directions it received. It also did not save the day's activities to the rover's long-term memory.

But three days hence the rover seemed to have recovered from the glitch on its own and is responsive to commands from Earth.

The Jet Propulsion Laboratory (JPL) team operating Spirit will begin diagnostic tests to determine the cause of Sunday's glitches.

"We don't have a good explanation yet for the way Spirit has been acting for the past few days," said JPL team leader Sharon Laubach.

One possible theory that explains the anomalies is that the rover's electronics could have been damaged by a cosmic ray - a fast-moving particle from the sun or elsewhere in the galaxy.

But whatever caused it, the problem appears to have corrected itself. And the rover Spirit is back to normal.