A vast dust storm blanketing about a quarter of the surface of Mars has threatened NASA’s Opportunity rover, plunging the solar-powered vehicle into what the space agency has described as a “dark, perpetual night.”

With its primary energy source obscured, the rover, which sits in the Perseverance Valley of Mars near the center of the storm, appears to have automatically entered a power-saving mode in which it will remain until the sun re-emerges, agency officials said.

“We’re concerned, but we’re hopeful that the storm will clear and the rover will begin to communicate with us,” John Callas, the Opportunity project manager, told reporters on a Wednesday conference call with other NASA officials.