The Phoenix mission just issued a statement announcing that, in response to a "low power fault," the spacecraft went into safe mode yesterday. This much was actually expected to happen because of the instructions sent yesterday to the spacecraft to turn off the heater that once kept the robotic arm and TEGA instruments warm. However, the spacecraft evidently surprised mission control by taking more self-protective activities than were anticipated, switching unexpectedly to the "B" side of its electronics. (Like Hubble and indeed most spacecraft, Phoenix basically has two brains, one of them kept unused until and unless its first brain fails. I wish I had that.) It also shut down one of its two batteries.
While in safe mode, the spacecraft quits executing any science plans and other non-critical activities, and waits for instruction from Earth. Within hours, mission controllers had brought the spacecraft out of safe mode and restarted battery charging. Although little if any battery power was lost, the mission is, conservatively, not performing any science activities for "several days to allow the spacecraft to recharge and conserve power. Attempts to resume normal operations will not take place before the weekend."
Although there is nothing wrong with the spacecraft's communication systems, communication does draw power, so all communications were canceled this morning; the next communication will take place this evening.
The energy conservation plan outlined yesterday hasn't changed, but the statement goes on to say that the mission has decided to turn off the second of five survival heaters, the one that served the lander's pyrotechnic initiation unit.
Again, I know I need to catch up on what Phoenix has done to date -- but I've got MESSENGER's science results to cover and I haven't even mentioned yet that Cassini has an image-rich flyby of Enceladus planned for Friday, so it may be a while.