We hope to get 15 centimeters resolution. That's unprecedented resolution.
Comets are far more than an intellectual interest. These things affect us, and may have even enabled us to exist.
It's an interesting object and it's raised some interesting issues, but a worrisome threat No. We've got plenty of time.
We're trying to understand the structure of a comet and also its composition. Once we hit it, we will open up surface areas that are exposed to the sunlight and see new subsurface ices for the first time.
Goodness, no. The closest fragment will be about six million miles away--or twenty-five times farther than the Moon.
The spacecraft has to be smart enough on its own to observe the comet, determine whether it's headed in the right direction, if not, make its own course correction, and then fire its thrusters to achieve that course correction.
This is a rare opportunity to watch a comet in its death throes from very close range.