A dust storm has reduced sunlight and visibility at the rover's location.
For two weeks, the storm has smothered the Mars Opportunity rover, turning day to night and blocking almost all light from reaching the robot's solar arrays.
A dust storm at Mars is now global, keeping NASA's Opportunity rover out of touch with Earth. NASA engineers think the rover is in a low-power mode, waking up only periodically to check if its batteries have recharged enough to phone home.
But a storm can't keep the Curiosity rover down.
It's unknown how long this dust storm will last, though previous Martian dust storms have persisted for weeks to months. The last tau for Opportunity's site was over 11. The atmosphere is so thick with dust, "accurate measurements are no longer possible for Mars' oldest active rover".
Nasa's Curiosity rover has beamed back pictures of a dust storm that has engulfed much of Mars over the last two weeks and prompted Nasa's Opportunity rover to suspend science operations, the United States space agency said today. Without a steady supply of sunlight, the biggest risk for Opportunity would be freezing in the Martian cold.
In the meantime, NASA scientists are maintaining a full-court press the Martian dust storm. The European Space Agency also has two spacecraft in orbit (Mars Express and the ExoMars Trace Gas Orbiter).
"We don't have any good idea", said Scott Guzewich, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Curiosity, a car-sized rover, runs on nuclear energy. NASA said Wednesday the storm now encircles the red planet, with only tall volcano peaks and the poles exposed to the sun. At left is an image from Curiosity's Mast Camera (Mastcam) taken on May 21, 2018, before the storm.
Though Curiosity is on the other side of Mars from Opportunity, dust has steadily increased over it, more than doubling over the weekend, NASA said.
Daily photos are being captured by the Curiosity rover's Mast Camera, or Mastcam, show the sky getting hazier.
You can get updates about the dust storm, and Opportunity's status, at NASA's Mars Storm Watch page.