Will an asteroid hit the Earth?

StarChild Question of the Month for July 1999

Question:

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Answer:

A number of recent movies have been about this subject. It is important to remember that they are just movies and often times do not represent good or true science. Sometimes, however, there is a tiny seed of truth behind a movie, although it may be hard to tell what is true and what is fiction. This is the case for the movies about asteroids hitting the Earth.

Let us say right away that at this moment, we know of nothing currently on a collision course with Earth. Last year, it was announced in the news that an asteroid was on a collision course with Earth and would hit in the year 2028. We now know that the calculations were in error and that asteroid will miss the Earth completely. You can read more about this at http://impact.arc.nasa.gov/news_detail.cfm?ID=60.

Keep in mind that the Earth has been hit before by asteroids and will be again someday. We don't know when, but we do know it is not in the immediate future.

Why are the chances of us being hit small?

Our solar system is very big compared to the size of the Earth, which means that the chance that the Earth will be hit by another solar system object such as an asteroid is very small. Once in awhile, it happens. But not very often.

Think about this, most of the asteroids in our solar system are located in the asteroid belt. Yet we have been able to send spacecraft such as Voyager I and II, as well as others, through this belt without any problems. Why? There is more "empty space" in the belt than asteroids!

How often do we expect the Earth to be hit?

The asteroids capable of causing a global disaster if they hit the Earth are extremely rare. They probably would need to be about a kilometer or more in diameter. Such bodies impact the Earth only once every 100,000 years on average. Other objects of a similar size, such as comets, impact even less frequently, perhaps once every 500,000 years or so.

If we discover an object that will collide with Earth's, what could be done about it?

If astronomers find such an object, there would be plenty of time to track it, measure its orbit precisely, and plan a system for deflecting it from its current orbital path. There would be no great hurry and no great panic. It would be a project for all the world's nations to take part in. Because we will have found it long before it actually intersects the Earth's orbit, it probably would take only a small push (perhaps from chemical rockets we land on the surface of the asteroid) to divert it from a threatening path.

Who is watching the skies?

There are agencies, NASA among them, which realize that although the Earth is in no immediate danger, an asteroid impact is something that will pose a problem sometime in the future. It is in the world's best interest not to ignore this, but to be watchful in order to provide the maximum warning time. You can find out more about some of the groups watching the sky for potentially threatening objects at:

The Near Earth Asteroid Tracking Team - http://neat.jpl.nasa.gov/
SpaceWatch - http://www.lpl.arizona.edu/spacewatch/
The Asteroid and Comet Impact Hazard Group - http://impact.arc.nasa.gov/

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