MadSci Network: Astronomy
Query:

Re: should i be afraid of asteroids

Date: Thu Nov 9 13:01:41 2006
Posted By: Jim Guinn, Staff, Science, Georgia Perimeter College
Area of science: Astronomy
ID: 1162230596.As
Message:

Dear Rebecca,

I think that the arguments against being afraid of asteroids are much 
stronger than the arguments in favor of being afraid of them, so Iíll 
start with those.

Most of the asteroids in our solar system orbit the sun in between the 
orbits of Mars and Jupiter, which is very far away from us.  There are 
some asteroids, however, that may come near the Earth, but the chances of 
them actually hitting the Earth are very, very small.  Compared to the 
amount of space in our solar system, the Earth is really a tiny object, 
and so itís a very hard thing to hit.  In the early stages of the 
formation of our solar system, there was a lot more material flying around 
than there is now, and so, back then, a lot more collisions took place.  
We can see the results of some of these by looking at the cratered surface 
of the Moon.  But that sort of thing is just not happening much any more.  
Think about what an unusual event it was when Comet Shoemaker-Levi 9 
collided with Jupiter (see for example
http://antwrp.gsfc.nasa.gov/apod/ap990814.html
and remember that Jupiter has about 125x the surface area as the Earth does, and
over 300x the gravitational attraction!

On top of all that, rather than leaving it to chance, there are many 
astronomers who track all of the known asteroids to make sure they arenít 
going to come too close to the Earth.  Take a look at the PHA (Potentially 
Hazardous Asteroids) site created by the 
Harvard Center for Astrophysics.  There are also 
astronomers all over the world who look for new asteroids, and whenever 
something unknown is discovered, its orbit is determined to find out where 
it is and where itís going.

To be honest, having an asteroid come near the Earth offers a great 
opportunity to study it.  Of course, we donít want it to hit us, but 
having it come close enough to send a probe to it can be very exciting!

If, at some time in the future, it turns out that something is heading 
directly for the Earth, then there are things that can be done about it.  
For example, an asteroidís course can be changed by sending a rocket up to 
it and giving it a little nudge.  The earlier it gets pushed, the easier 
it would be to move the asteroid away from the Earth.  Adjusting its orbit 
just a little bit can keep it away from the Earth for millions of years.

So what are the arguments in favor of being scared of asteroids?  Well, if 
one really did hit us, it could cause a tremendous amount of damage.  It 
is quite possible that the extinction of the dinosaurs was caused by an 
asteroid impact.  With the current state of development of coastal regions, an
impact of even a small asteroid in the ocean would cause tidal waves that would 
devastate coastal communities.

Well, Rebecca, do I think you should be afraid of asteroids?  Definitely 
not!  There are plenty of astronomers who spend their nights making sure 
that none of them bother us.

I hope that answers your question.  Please let us know if you would like 
any more information.

Thank you for your interest.

Sincerely,

Jim Guinn
Georgia Perimeter College





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