Averting Armageddon - questions and answers

How many large impacts have there been since the Earth was formed?

The Earth itself was created from collisions between early solar-system material. When the Earth was young, huge asteroid impacts were constant. One of the biggest of these collisions is thought to have created the Moon. As time went on, and the planets formed from debris, fewer and fewer large chunks were available and the frequency of big impacts fell.

Since life evolved on Earth, large impacts are thought to have killed-off a significant share of life on the planet. The Earth has been hit countless times - it's just that mountain building, the sea and erosion mean that we can't see the vast majority of the craters.

Learn more about what killed the dinosaurs on the Walking with Beasts site.

Could a large asteroid impact change the orbit of the Earth?

There aren't any asteroids left from the formation of the Solar System that are big enough to do this. The entire asteroid belt put together adds-up to only about one-thousandth of the Earth's mass.

However, this could have happened in the early stages of the Solar System. The fact that Uranus spins on its side is probably because of a huge asteroid hit early in its existence.

If an asteroid landed on the other side of the world, how would this affect me?

If a large asteroid hit anywhere on the planet, it's not just people near the impact who would suffer the consequences. The blast would send huge clouds of dust and rock into the atmosphere. As this re-enters the Earth's atmosphere it would burn up and this would gently heat the Earth.

In addition, dust would hang in the air for years causing global darkness. Global agriculture could be wrecked and the world economy would be adversely affected. So even for the survivors life could become a great deal harder.

Would an impact in the sea be less dangerous than an impact on land?

It might be slightly better for humanity if an asteroid landed in the sea, and less debris was blasted into the atmosphere. However, it's unlikely to be much better. An impact could create huge tidal waves. Given that much of the world's population, and many of it's largest cities are on the coast, the consequences could be just as disastrous.

Why do most asteroids lie between Mars and Jupiter?

The huge mass of Jupiter is the critical factor as to why the asteroid belt is where it is. The asteroids in the belt are the remains of a 'failed' planet that never successfully formed because of gravitational interference from Jupiter. Since the beginning of the Solar System, most asteroids outside the main asteroid belt have either been flung out of the Solar System by interference from Jupiter's gravity or gathered together in the formation of the planets.

Explore the asteroids on the Space website

Is Britain doing anything to combat the threat of asteroids?

The UK Government did instigate a Near Earth Object Task Force. It concluded that the risk of impact was very real, and recommended that a global programme of telescopes be dedicated to searching the skies. So far, the recommendations have not been taken up.

Globally, it is very difficult to know what can be done to combat the threat of asteroids. Most eyes look to the United States but NASA is essentially a science organisation, not a defence body. Some feel the United Nations should also take charge.

Can I see asteroids through a pair of binoculars or a telescope? Can I see 1950 DA?

Occasionally - about once every 50 years - asteroids pass by the Earth close enough to be seen with a telescope or good pair of binoculars. 2002 NY40, which passed near Earth in August 2002, was one of them. It wasn't easy to spot, however: you had to know where in the sky to look and it appeared as a slow-moving dot of light fainter than any of the stars in the background.

1950 DA is too far away from Earth to see without using top of the range astronomical instruments. Most of what we know about it comes from radar.

Find out what you can see in the night sky tonight

Can I help look for dangerous asteroids?

The more eyes on the sky, the better. Many amateur asteroid hunters feed their information to the Minor Planet Centre, based at Harvard University Boston, USA. Researchers there use amateur observations from all over the world to help measure the orbit of asteroids, and hopefully, to rule out any threat to the Earth.