1. Comets are probably left over from the time when the planets formed.
Small Bodies in the Solar System
Comets
A small body of ice, rock, and cosmic dust loosely packed together is called a comet. Some scientists refer to comets as “dirty snowballs.”
Comets are probably left over from the time when the planets formed.
Comet Tails When a comet passes close enough to the sun, solar radiation heats the ice so that the comet gives off gas and dust in the form of a long tail.

2. Small Bodies in the Solar System
Comets, continued
Comet Orbits The orbits of all bodies that move around the sun are ellipses. Ellipses are circles that are somewhat stretched out of shape.
A comet’s ion tail always points away from the sun due to solar wind. Dust tails do not always point away from the sun.
Comet Origins Scientists think that comets come from the Oort cloud that surrounds the solar system. Comets also exist in the Kuiper belt beyond Neptune.

3. Comets come in a wide range of sizes
Comets come in a wide range of sizes. The largest nucleus observed is about 25 miles, or 40 kilometers, in diameter. The dust and ion tails can be enormous.
Small Bodies in the Solar System
Comets, continued

4. Small Bodies in the Solar System
Asteroids
What Are Asteroids? Small, rocky bodies that orbit the sun are called asteroids. They range in size from a few meters to more than 950 km in diameter.
Most asteroids exist in the asteroid belt, a region of the solar system between the orbits of Mars and Jupiter.

5. Small Bodies in the Solar System
Asteroids, continued
Types of Asteroids. The outermost asteroids are richer in organic material, while the innermost asteroids are more stony and metallic.

6. Small Bodies in the Solar System
Meteoroids
A meteoroid is a small, rocky body that revolves around the sun. They are similar to but much smaller than asteroids.
Meteor Showers You can see a large number of meteors when the Earth passes through the dusty debris of comets.
A meteor is a bright streak of light caused by a meteoroid falling through Earth’s atmosphere. These “shooting stars” are dust- to pebble-sized particles burning up from friction.

7. Small Bodies in the Solar System
Meteoroids, continued
Types of Meteorites A meteoroid that falls through the atmosphere without burning up completely and strikes the ground is called a meteorite.
Like asteroids, meteorites have different compositions. There are three major types of meteorites: stony, metallic, and stony-iron.

8. The Role of Impacts in the Solar System
Small Bodies in the Solar System
The Role of Impacts in the Solar System
An impact occurs when two bodies collide in space. Often the result is an impact crater.
Planets and moons that do not have an atmosphere receive many more impacts. Earth’s atmosphere burns up many meteors that might otherwise result in impacts.

9. http://www. universetoday