We haven't found a single impact crater on this image. Pluto is being bombarded by other objects in the Kuiper belt; craters happen. Eyeballing it, we think it has to be under 100 million years old; it might even be active right now. Mountains are up to [3500 meters] high. We know the surface of Pluto is covered with nitrogen and methane and other volatile ices; you can't make mountains out of that stuff. We are seeing the bed-ice of Pluto. Water ice is strong enough to hold up big mountains, and that's what we think we are seeing here.

What's particularly exciting to me about this is that this is the first time we've seen an icy moon that isn't orbiting a giant planet. We usually attribute strange features on icy worlds to tidal heating. That can't happen on Pluto. There is no giant body that can be deforming Pluto on a regular basis; Charon is too small to do that. This is telling me that you do not need ongoing deformation from a giant planet to power deformation on an icy body. That's a really important discovery that we just made this morning.

We will have more of this mosaic to show you on Friday.

We have no idea at this point how mountains formed. Triton doesn't have this kind of rugged terrain. It has a lot of strange materials, but it doesn't look at all like this.

The terrain to the lower right looks really strange. It's like piles of stuff with grooves on it. It's baffling in a very interesting and wonderful way. I don't think it looks like the surface of a lava flow, but perhaps a similar process happening on a much larger scale.

[In response to a question about how Pluto and Charon could retain heat for so long]: We have a couple of options. We know there's radioactive material inside Pluto and Charon; radioactive heat is powering geology inside the Earth. It may be telling us that even small bodies, if they're icy, can store heat. Maybe they can store heat for a long period of time.