Summary: Despite the rover not being turned on again, astronomers are still learning new things about the chosen comet. For instance, it's changing rotation speed. The comet takes approximately 12.4 hours to complete one rotation, only that rate seems to be slowing down by one second per day. It seems like a small change but that is big in astronomical terms. It is actually a faster rate of change than in September. Back then it was slowing down by 33 milliseconds per day. (And right there is a differential equation for those who are so inclined.)
Scientists know the reason for this. The comet 67P is becoming more active which means there are gas jets shooting out of the rock and serving as propulsion, much like a rocket, only in the opposite direction of rotation, thus slowing it down. The jets actually shoot out of the comet at 800 meters per second and extend a few kilometers off the surface.
Astronomers found this out thanks to Rosetta still being in orbit around the rock. In order to keep the satellite in the correct trajectory, the navigators were using a system of landmarks on the surface to keep track of position. Only the landmarks were coming into view at a different time than expected.
BBC News
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