A huge dust storm has forced Nasa’s solar-powered Opportunity rover into a dormant state, space engineers say.
The unusually intense storm has blotted out the Sun over a quarter of the planet’s surface, Nasa said.
Agency officials say they are “concerned” after the nearly 15-year-old robotic explorer shut down almost all its functions.
They say they hope the rover will wake up once the storm has passed.
John Callas, Opportunity project manager, said the rover had “fallen asleep and is waiting out the storm” in an area called Perseverance Valley.
He said dust was accumulating in a thin layer and was not expected to completely bury the rover.
“We are concerned but we are hopeful that the storm will clear and the rover will be able to communicate with us,” he told a news conference.
“In this point we are in a waiting mode,” he added. “We are listening every day for possible signals from the rover.”
He likened the feeling among his colleagues to that of waiting for a loved one to emerge from a coma.
“If it was your 97-year-old grandmother you would be very concerned – and we are,” he said.
Mission engineers believe it will be several days before the rover will receive enough sunlight to charge back up.
Opportunity landed on Mars in January 2004 and Nasa says it has proved tougher than expected having been designed for only a 90-day mission.
Its discoveries include evidence that, at some point in the past, conditions in at least one area of Mars could have been suitable for sustaining microbial life.
Another Nasa rover, Curiosity, which has been exploring Mars since 2012, is not solar powered and has not been affected by the storm.