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.

You've got the same problem as a car on Earth on a sheet of ice. There is very little friction between the wheels and the surface.

It's an interesting object and it's raised some interesting issues, but a worrisome threat? No. We've got plenty of time.

It takes 7 1/2 minutes for a signal to get from Earth to the spacecraft and another 7 1/2 minutes to get back. So, we can't joystick this spacecraft like a video game.

There's a certain amount of nervousness at present. ... It's a harsh environment out there and this is not easy. We don't really know what to expect, frankly. ... It could be anything from a crater the size of a football stadium to something that's far more modest. Or the spacecraft could simply bury itself into the comet.

Comets are far more than an intellectual interest. These things affect us, and may have even enabled us [to exist].

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.

We hope to get 15 centimeters resolution. That's unprecedented resolution.

They could be the watering holes and fuel stations for future interplanetary exploration.