Comet's Tale:  Their Place in Space
 Where do Comets fit in? 

By now you know a lot about comets: where they come from, what they're made of, what they look like, and why they look that way.  But there are other objects in space that are not planets or moons.  What do comets have in common with them? How are they different? For example:

Are Comets and Meteors the same thing?

Have you ever seen a shooting star? Shooting stars are also called meteors, and we know that they are not stars at all. In fact, they look like very fast moving comets. A meteor may in fact have once been part of a comet.

As a comet travels near the Sun, developing its coma and dust tail, it can lose several hundred million tons of dust and vapor. The closer it gets to the Sun, the more solids and gases are released. This material remains in orbit about the Sun, and the solid pieces themselves are called meteoroids. A meteoroid becomes a meteor when it falls through the atmosphere, and we see it shoot across the sky.

Most of the meteors left behind by comets are very small.  These small objects hurl through the atmosphere so fast that they heat up and actually burn very brightly. This is similar to what happens to spaceships as they re-enter the atmosphere --they get very hot, and the astronauts must be protected from the heat. Most meteoroids are completely burned up in the earth's outer atmosphere.  But every now and then, large meteors make it all the way to the groundóthen they are called meteorites.  A meteorite type called Chondrite

An Iron type meteorite

Cross section of another type of meteorite

Meteor Showers: space weather from comets

When Earthís orbit passes through a trail of comet debris, there are many meteors visible in a single night--a meteor shower.  The Earth passes through the meteoroids from the comet in the same place each year as it goes around the Sun, so meteor showers occur annually. For example, every August we can see the beautiful Perseid meteor shower, caused by the dusty trail that Comet Swift-Tuttle left behind. meteoroids along a comet's orbit, crossing the earth's orbit


A high density Leonid Shower, 1998, photograhed from a plane

Photo by Lorenzo Lovato

The picture of the Leonid Meteor shower to the right was taken in 1998 from an airplane.  The Leonid meteors appear every November, and seem to come out of the constellation Leo, the lion. They are pieces left behind by comet Tempel-Tuttle.  


  Are Comets and Asteroids the same thing?

Ida-- a mid-sized asteroid at 58 x 23 km, has its own satellite asteroidAsteroids are sometimes called minor planets.  They are small, rocky worlds. Most of them orbit the Sun between Mars and Jupiter in what is known as the asteroid belt.  Since they are not made of frozen gases like comets, asteroids donít form a coma of bright, heated gas.  Since they donít have a coma, they canít form glowing plasma tails or dust tails that reflect light. Asteroids are very difficult to observe, even with a telescope, because they reflect only tiny amounts of sunlight, but they are now being studied using satellites.

This is the end of our comet overview. But wait--do you think really big meteorites, asteroids, or even comets ever hit the earth? What would that be like? Click Continue to go on to "Killer Comets?" 

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