Amanda Adams asked:
I heard recently that there may be cryovolcanoes on Pluto. This was explained to me as ice-volcanoes where instead of magma, molten rock, there is water. But what is the difference between ice and rock? Ice is frozen water.... Rock is frozen magma. Right? Is there a fundamental difference?
Chris Smith put this to Professor Marian Holness, geologist from the University of Cambridge...
Marian - No, there isn't. Letís just step back a bit and talk about Pluto for a minute. These messages that are coming pixel by pixel for the last year or so. So Pluto is extremely cold. Its surface is about minus 200 degrees centigrade. So, what's the surface of Pluto got on it? Well, itís ice essentially. There's water ice which is fairly rigid. Itís like the bedrock of Pluto is water ice. And then there are some ices that move around a lot. There's nitrogen ice and there's carbon monoxide ice. And then moving around, they're sublimating and then they're condensing somewhere else.
The reason I'm telling you all of this is because if you look at the topography on Pluto, there are mountains and ridges and bumps, and lumps. If they're old, theyíve got craters on them. Thatís how we know they're old. They must be made of bedrock. There are these two mounds which they found. They're not mountain ranges. They're just isolated circular mounds and they're about 150 kilometres across and they're about 6 kilometres high. Now that's a pretty big mound. Weíve got some things vaguely similar to that like Hawaii on Earth Ė the biggest volcano on Earth.
Anyway, there are these things. Because they're really big, they must be made of something strong. So they're probably made of water ice. Theyíve got a central depression in the middle. They look just like a volcano, a really big hole in the middle which is what a volcano looks like. And their surface has not got many craters on it. so they're quite young, but itís got a very curious sort of hummocky texture. Thatís essentially all we know. Itís pure speculation. Weíre just saying the shape of these things looks like a volcano but we donít know any more than that. Itís just very exciting science.
Exploding plumes of material (a volcano) relies on material which is heated sufficiently to turn into a liquid and/or gas, but then cools down into a solid, close to the source.