By analyzing the returned signal and how the radio waves are reflected and scattered back as they travel through the comet, scientists will be able to study the interior of C-G's nucleus.
The craft has spent another 10 years in flight as we've waited for it to reach its prime target, Comet C-G, this August.
We hope that C-G's activity level is still low when Rosetta arrives, so that the spacecraft can get close to the comet to do detailed mapping, select a landing site, and deploy Philae safely.
The mission will spend an unprecedented amount of time close to C-G, studying how its activity turns on, how much of the surface is active or if that activity is primarily from discrete jets, how the nucleus interacts with the "collisional region" (the inner part of the coma where the gas density is high enough for collisions between atoms and molecules), and how all of that forms and drives the coma and tail.
Depending on C-G's activity level, Rosetta might only have a few months in which to orbit the comet at distances less than 50 km.
Comet C-G is a Jupiter-family comet, meaning that its orbit is "controlled" mostly by Jupiter.
C-G has a short orbital period of about 6.5 years and a rotation period of about 12.4 hours.