Shortly before the loss of communications with Hitomi, the U.S. military’s space tracking radars detected five objects in the vicinity of the satellite. The Joint Space Operations Center, the U.S. military command charged with monitoring objects in orbit, said the debris came off the Hitomi spacecraft around 0520 GMT (1:20 a.m. EDT) Sunday.
It's not clear exactly what happened to the satellite, but scientists have a few guesses. Orbital debris might have smacked into Hitomi and knocked a few pieces loose, or the satellite itself might have suffered some sort of explosion from the inside.
Although communications are down, JAXA did receive a brief signal from Hitomi after the debris was detected. Hope is not lost yet, and the agency is working to recover communications.