The simple answer is that we can. However the problem is that it uses loads and loads of energy. There are two ways of doing it. You can either boil up the water into steam and then recondense it into water. Obviously that's going to use loads of energy, as you can see how expensive it is to boil a kettle. The other way of doing it is something called reverse osmosis. This is when you take a really fine filter and push the water through it. The salt then stays on the other side. This is a lot more efficient than boiling it, but it's still very energy expensive. Considering that the greenhouse effect is a big problem because we're using too much energy already, if started producing water by desalination in one way or another, we'd really be in trouble. There's no such thing energetically as a free lunch and what you're trying to do is take salt water which has a great concentration of minerals in it and separate those minerals into a strong concentration of minerals and a strong concentration of water. In other words, you've got to do work to sort the wheat from the chaff. That work comes at a high price. If we do it, we have to burn a fossil fuel in some way or another. The sun does that almost all the time all around the Earth. The sun is hitting the surface of the ocean, evaporating some water and leaving behind the minerals in the sea. The water forms clouds and then comes to Earth as precipitation. So the sun is desalinating all the time, but then the sun has money to burn.

We've obviously got one natural satellite, our Moon. But we've actually launched around 8000 artificial satellites up into orbit around the Earth. However, that's not all there is orbiting around the Earth. As well as these 8000 solid lumps of whole satellite that are up there, we've got lots and lots of little bits of junk swirling around. Now that can be anything from a nut and a bolt that's been lost to astronaut gloves that have been lost during space missions. This stuff can actually be quite a problem, because as it's up there whizzing around at kilometres per second, if it hits another satellite it can seriously damage it and blow some more bits off. So all the time this stuff is accumulating, but there's no easy way to go up and remove it. Eventually all of it will slow down and fall into the Earth but it's up there for a long period of time.

In 3D glasses, one lens is one colour and the other is another colour. Now when they project the film, they have a very powerful projector that projects two images side by side. One of the images is very slightly displaced from the other one. The reason for this is that you've got two eyes looking at the world and so you're getting two images of the world reaching your brain. These are slightly overlapping but separated by a small amount, or by the distance your eyes are apart. On the screen, they're projecting these two images: one in one colour and the other in a slightly different combination of colours. What your glasses do is to screen out the colours of one of the images while allowing the colours of the other image through. When your brain recombines them, it's seeing two different sets of images overlapping each other in just the right way to recreate a three dimensional image. If you shut on eye and move your head from side to side, the world looks slightly different. Things close to you move differently from things far away and that's one of the ways your brain judges how far away things are. The way they make the films is that they have two film cameras maybe six inches apart and that produces the same effect as looking through two different eyes.

If you look at the Earth from above, then it's going around anticlockwise. Now the obvious question is 'which way is above in the vacuum of space'? How do you define that? Well if you're looking down on the Earth onto the North Pole it's going anticlockwise. The sun is also spinning. It goes around every few hours and is actually moving around through the galactic disk around the galactic centre. The galaxy is also spinning, so our sun is making a grand tour of the galaxy I think every few million years. Of course, the Milky Way is also moving through the Universe so everything is moving and it's all down to what you perspective is on that.

The Earth has been spinning ever since it was created. It could have been because the Moon was created after a big collision with the Earth. If the collision was just off centre, then it would have spun the Earth really fast. When the Moon was created, it was really close to the Earth. The tides are actually slowing the Earth down. In fact, two hundred million years ago there were about 400 days in a year. This is actually a legacy of how all our planets formed because there was a big disk of material going around the sun and everything was spinning. As everything coalesced and formed planets, the conservation of momentum meant that they carried on spinning. This is the same principle as when an ice skater spins and brings their arms in and spins faster.

Well that's actually a really good question but there are a few effects that you need to take into account here. The Earth and meteorites are going around the sun and in different directions and at different speeds. Every now and again, you get a crossing of paths and one hits the other so we get a meteorite landing on the Earth. It's this crossing of paths that is more important than the gravity of the Earth itself. There have been a few near misses that nobody knew about until someone took a photo of the night sky and saw a meteorite. There are millions of little meteorites that hit the Earth all the time.

I've just been doing a quick calculation. If a tyre lasts for about five years, I reckon it comes out at about 10 000 tonnes a year of rubber in the UK. Tyres are actually really bad polluters because they don't only contain rubber but also a lot of heavy metals too. That's why when people say let's just burn old tyres, it's really bad because the toxins go up into the atmosphere and drop out into the soil that animals eat. If we focus on the US, 300 million people live there. Let's assume that they all have two cars per family of four. A car has four wheels, which means that in the US at any given time there are probably roughly 600 million tyres in use in any given year. Let's assume that the tread on a rubber tyre is 10 centimetres wide, the circumference of the wheel is 3 metres, and the thickness of the tread is about a centimetre. That means that the volume of rubber on a wheel and rubbing out is about 3 litres. If there are 600 million tyres and you times that by 3 litres, and then convert that to metres cubed, that's a staggering 2 million metres cubed of rubber every single year just in America. The density of rubber is 1200 kilograms per metre cubed. That means that there are 2 billion kilograms of rubber in tyres in the US. If you assume that they last for four years, that means that roughly two billion kilos gets lost or worn out every four years. That's a staggering amount.

You're right for ice that's floating on water because it doesn't change the volume at all. But if you've got ice on Antarctica or the Greenland ice sheet where it's on rock and nowhere near the sea, when that melts, it will end up in the sea and increase the volume of the sea. Greenland is a massive ice sheet and there are tonnes and tonnes of water locked up as ice on land. The melting of ice on Greenland is raising the ocean depths by about half a centimetre every single year. If all that lot goes in the next 100 years, we could see a one metre rise in sea level.

It's actually requires a lot of power. We use huge big radio dishes and they are metres across, if not nearly kilometres. We use a large number of these in order to communicate with spacecraft. There is a large time delay. I was involved with the Huygens mission which was at Saturn and there was a delay of a few hours for the data to get back to us. Because of that we had to use everything on remote and we got the data afterwards. We had no direct control while it was actually happening.

The easy answer is never because the New Horizons spacecraft is actually going to go into orbit around Pluto so it's going to stop there and isn't going to go any further out. But the Voyager spacecraft are actually at an immense distance away now. They're actually outside our solar system and in interstellar space, so we will be really hard pressed to get something out that far again. They really are the furthest thing that we've ever sent out into space.

You would have to hold on but not because it's moving but because the gravity is so low on an asteroid. In fact we've launched the Rosetta mission that's going to land on CG, which is its short name, and that's going to have harpoons on it to lock itself onto the asteroid. If it didn't then it would just float away.

The reason why we use huge dishes is because the space probes use small dishes that send weak signals. They are even weaker by the time they get here, so we have to have big radar dishes to hear them.