If you look at a hand grenade, it looks a bit like an egg. It's got a hard metal shell around the outside and it'' packed with high level explosives. At the top there's a trigger, and on the trigger is a really big spring. The spring pushes down on a hammer which pushes down inside the hand grenade. When you hold the handle closed and the pin is in it, it's compressed and can't go anywhere. As soon as you pull the pin out and let the handle up, it drives the hammer down inside the core of the hand grenade. In the bottom of the core is a detonator and it fires that off and lights a fuse. The fuse burns slowly for however long the grenade has been designed to burn for and that fuse detonates the main detonator and charge. This occurs a certain time later. The idea is that you know roughly how long it takes to go of, because when you lob it, it doesn't give the enemy an opportunity to pick it up and throw it back to you.

Asteroids are tumbling in space and spinning around and an interesting thing is that they're all spinning rather slowly. That is consistent with them being loose piles of rubble. They're not solid objects. When meteorites come to Earth, they tend to travel pretty fast, around twenty kilometres per second, although the maximum is seventy. The net result of that is that they make this wonderful fireball effect. If a big one comes, the atmosphere doesn't slow it down, and that's when trouble happens. It will come all the way down to the surface and explode. On eof the nest studied meteor craters is in Arizona and it's just over a kilometre wide. The object there was about thirty metres wide. The estimate for the asteroid that wiped out the dinosaurs is ten kilometres.

It could vary. Communication is big business in terms of satellites, so that could have a very large impact. I wouldn't be so upset about losing some of the television channels! In terms of other impacts, I think we could usually work around them. As a scientists I spend my life trying to figure out ways of working around problems so I don't think it would be the end of civilisation but I think money changers would be brought to its knees for a while, but we would definitely recover.

It's more likely to be a planet. When planets travel through a large depth of atmosphere, they appear to twinkle. Sometimes they twinkle very bright colours. You will eventually lose sight of it as it's orbiting around the sun.

The reason why we send dogs into space is because they are so intelligent. You can train a dog to do all sorts of things, and so that's why we want a dog to go up there and give us feedback. They're very bright!