Space 'scope Kepler is running in emergency mode and NASA doesn't know why.
Kepler's status was discovered during a routine communication, NASA said.
The agency announced a spacecraft emergency on April 9, and says it believes Kepler entered emergency mode around 36 hours before that.
Declaring a spacecraft emergency gives Kepler's personnel priority access to the Deep Space Network while they try to communicate with the craft and work out what's wrong.
Mission operations were preparing to point Kepler at the centre of the Milky Way, as part of a campaign to collect microlensing observations.
As NASA notes: “The spacecraft is nearly 75 million miles from Earth, making the communication slow. Even at the speed of light, it takes 13 minutes for a signal to travel to the spacecraft and back.” ®