Historic Rosetta spacecraft images target comets halo - space - 15 May 2014 - New Scientist
Rosetta launched in 2004 and was woken up in January this year after a three year slumber. Now ESA is activating its instruments and putting the probe through its paces in preparation for the final approach to the comet in August.
The craft is still 2 million kilometres away from the comet, but the pictures it took of the comet "waking up" have helped researchers determine its rotation period. It turns out the comet completes a full turn every 12.4 hours, about 20 minutes shorter than previously thought.