As I write this Cassini is conducting it's closest flyby yet of Saturn's mysterious moon Iapetus.
Iapetus is a mystery for two reasons; firstly it has one dark hemisphere and one light hemisphere (visible at the top is this photo) giving it the nickname of the Ying-Yang moon, secondly it has a massive mountain range around it's equator. This mountain range makes it look as if the moon is constructed from two hemispheres joined together (a bit like an easter egg). This of course is highly unlikely to be the real reason, but that's one of the things this current encounter should help to solve.
During this encounter Cassini will fly within 1,000 miles of the surface of the moon, much closer than the previous closest approach of 80,000 miles in 2004. Emily Lakadawala has posted an article with all the details on the Planetary Society website and will be giving regular updates on her blog.