The Mars Phoenix Lander has started to shut itself down as the Martian winter approaches. With the days becoming shorter, it's getting less and less power from its solar panels that powers its electronics and its five heaters. To conserve power, it has shut down operation of its first survival heater, which had been keeping some of the lander's electronics within a reasonable temperature range.
All except one of the survival heaters will be switched off one by one as the available power decreases, with more and more instruments being exposed to temperature extremes. NASA will be stretching it out as much as possible to keep the lander operational. However, we are already seeing operations deteriorate as a power fault has forced the lander to switch to using backup systems.