MadSci Network: Astronomy

Re: Is it possible to change a metheorit's rate, avoiding colision with earth?

Date: Fri Oct 30 17:43:58 1998
Posted By: Richard Goode, Secondary School Teacher Physics, Porterville High School, CA
Area of science: Astronomy
ID: 909223421.As

"If the earth is at a meteorite's rate (course), how could we avoid the colision (in case it's possible...). I heard that in 2013 (?) there are a big chance of the earth colid with a meteorite; i would like to know what chances do we have to change it's rate, and, if we do, can we predict the new rate (the new course)?"

Asteroids that cross the orbit of the earth are a very real hazard. Unfortunately, we are not spending a lot of effort looking for them. The earth will again be hit by an object from space. This fact became more real a few years ago when Comet Shoemaker-Levy 9 hit Jupiter. The earth does get hit every day by small objects as we orbit the sun. Most of these are very small [about the size of a grain of sand] and we see them as "shooting stars" or meteors. Larger objects strike the earth less often.

[There are two kinds of objects that could cause damage to the Earth: asteroids and comets.] Astronomers have cataloged only a handful of the asteriods that could do considerable damage to the earth. These objects range in size from a few hundred meters in diameter to a few kilometers in diameter. Solid objects this size are hard to detect. It is estimated that we have located less than ten percent of these bodies. Comets might be easier to spot because they emit gasses which can make them easier to see at a greater distance.

In order to change the course of an object we have to find it first. The earlier we find it, the better chance we have to alter its path. Recently, astronomers found an asteroid that appeared to cross the orbit of the earth. It appeared that it was going to be near enough that it might hit the earth in the next century. Other astronomers searched old pictures, located the same asteroid, and were able to calculate a more accurate orbit. They found that it will still come close but miss the earth by several hundred thousand kilometers. [However, this episode illustrates the importance of searching for hazardous objects now. We can predict asteroid and comet orbits years, decades, even centuries in advance. If we find an object now, we may have several decades to a century to figure out what to do about it.]

There is no known object that is in danger of hitting the earth at any time in the near future. Of course, a new object could be discovered or a currently known object could have its orbit changed [by gravitational interactions with other planets].

Once we have determined that an object is in danger of hitting earth, there are several ways that we could possibly change its path and keep it from hitting the earth. These include nuclear weapons, laser beams, and attaching rockets to the object. There are problems with each and right now none of these are practical. [However, the objective of each method is to change the course of the object, not try to destroy it. Trying to destroy an object, by exploding a nuclear weapon on its surface might cause more problems.] The nuclear blast might not deflect it but break it up into smaller pieces. Instead of one large object we would have several smaller objects hitting earth. [Another reason for trying to detect objects now is that it would not take much of a deflection to make the object miss the earth. Think about being in a car: Is it easy for the driver to avoid hitting an object if the driver sees the object when it is a kilometer away or when it is a meter away?]

[Changing the course of an object by putting rockets on it seems pretty obvious. Using a nuclear blast or a laser to change the course of an object would probably be done in the following manner.] The laser would heat a small place on the comet and cause a jet of gas that could change the course of the comet; [the nuclear blast would be designed to occur just above the surface of the object, heating the surface, and again causing a small jet of gas.] Using a laser would require a more powerful laser than we currently have and the ability to target it over possibly millions of kilometers.

Of the various methods, attaching rockets would probably be the easiest to do. We would need small thrusting type rockets to attach themselves to the body and gently change the orbit. Again we would need to develop a system to deliver the thrusters to the body when it is far enough away to save earth.

Once the path of an object is changed, it is a very easy task to measure it's new orbit and calculate it's position several years into the future.

Can we change the path of a large object threatening earth? It depends on how much warning we have. Comet Hale Bopp gave us about two years warning. We might be able to solve that one if it threatened. Comet Hyakutaki gave us a few months warning. We most likely would not have been able to solve that one in time.

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