Last week, NASA's Curiosity rover on Mars suffered from an issue with one of its on-board computers, and had to be put into safe mode while the problem was resolved. Earlier this week, the rover was brought back fully online. Now, once again Curiosity is in sleep mode after NASA decided to put it into sleep mode due to the threat of a giant solar flare due to hit Mars later this week.
The solar flare, which is called a coronal mass ejection, or CME, was spotted by NASA just a couple days ago. The CME is heading towards Mars, and Curiosity is in the hot zone, so NASA decided to put the over into sleep mode to help protect against the potential damage from radiation. Fortunately, the radiation from CMEs is not typically harmful to rovers.
The first time that Curiosity faced a solar flare was in 2012 during its trip to Mars when it was blasted with a class M1 ejection. There is a possibility that Curiosity could be damaged, but there isn't much that can be done other than wait and see.
This latest setback is the second of Curiosity's mission, with the first being the main computer failure last week. The on-board computer became corrupted, which forced NASA to use the backup secondary computer instead. They put the rover into Safe Mode temporarily while working on the issue.