Comets, Asteroids, and Meteoroids

Learning Objectives

By the end of this unit, you will be able to explain the characteristics of comets, asteroids, and meteoroids, including their composition, orbits, and their impact on Earth.

Comets

Comets are made of frozen rock, dust, and gases. Like asteroids, comets are made of the leftovers after planets of the solar system are formed.

Comets orbit the Sun, as asteroids do.

Click here to watch a video on comets.

Comets can sometimes get so close to the Sun that they become hotter and bigger—even the size of a planet. When that happens, the comet has a "tail" of dust and gas up to tens of thousands of miles long.

Some comets do not survive when they get close to the Sun, and they fall apart into the Sun.

Scientists believe that comets may have brought materials needed to help life get started back when Earth first formed.

Comets do not crash into Earth as often as asteroids, but scientists still want to know if a comet might hit Earth.

There are two places in our solar system where comets are formed:

• The Kuiper Belt is around Neptune. It has the shape of a disk.
• The Oort Cloud is around our solar system.

Comets Have Three Parts

1. Nucleus - the solid core of the comet

2. Coma - the outer layer of dust and gas around the comet

3. Tail - as a comet orbits past the Sun, the solar winds from the Sun push the gas (bluish color) and dust (white) from the comet away, forming the comet's tail. A comet's tail is its most distinctive feature. As it approaches the Sun, it develops an enormous tail of luminous material that extends millions of kilometers away from the Sun. When far from the Sun, a comet's nucleus is very cold, and its material is frozen.

Asteroids

Asteroids are rocky and made of metals. Like Earth, asteroids orbit the Sun. But they are much smaller than planets and have a rockier surface.

Asteroids are made of materials left over when other objects in the solar system are formed.

Asteroids have gravity but no atmosphere. Some asteroids have small moons. The asteroid Ida, which is 19 miles across, has a moon called Dactyl, one mile wide.

Click here to watch a video of the Asteroid Belt.

A ring of asteroids, called the Asteroid Belt, can be seen in the sky between Mars and Jupiter.

Scientists study the orbits of asteroids to predict if they will crash into Earth. When an asteroid is located in space, scientists track where it goes over time. It is possible to tell if an asteroid moved from one place to another, but nobody knows how it got there. Many orbits are possible. Even after watching an asteroid for a full orbit around the Sun, scientists cannot say where it will go. The gravity of nearby objects and unexpected collisions could change its course.

Meteoroids

Have you ever seen a shooting star at night? Shooting stars are not stars. They start as meteoroids made of space debris, rock, iron, and/or nickel.

When asteroids hit planets, the pieces that result are called meteors.

Click here to watch a video on Meteoroids, Meteors, and Meteorites.

Meteors are meteoroids that hit the atmosphere of a planet. Meteors are called meteorites when they hit a planet's surface.

Because they are made of metal, meteoroids work like magnets.

Scientists study meteorites to learn more about how the universe formed and what makes up Earth.

Click here to complete an interactive from New Path Learning.