1. Other Objects in the Solar System
Chapter 24
Section 4

2. Comets
Bodies of rock, dust, methane, ammonia, and ice that orbit the sun in long ellipses.
Examples:
Haley’s Comet
Passes by the earth every 76 years (last seen in 1986).
Comet Hale-Bopp
Discovered headed toward the sun in 1995 by two amateur astronomers.

3. Comets Parts of a comet: Head Tail Core Coma
Solid part of the comet.
Usually between 1 and 100 km in diameter.
Coma
Spherical cloud of gas and dust surrounding the nucleus.
Formed when heat vaporizes ices of water, methane, and ammonia as the comet approaches the sun.
Can extend up to 1 million km form the nucleus.
Sunlight reflecting off the coma gives a comet its bright appearance.
Tail
Consists of gas and dust that stream out from the head of the comet.
Formed when the solar wind (electrically charged particles from the sun) push gas and dust away from the head of the comet.
Always trails away from the sun.
Can be more than 80 million km long.

4. Comets Oort Cloud Proposed by Dutch astronomer Jan Oort.
A large collection of comets that surround the solar system outside the orbit of Pluto.
These comets are either pulled into smaller orbits by the gravity of the sun or are pulled out of the solar system by the gravity of nearby stars.

5. Meteoroids
Small bits of rock or metal which move throughout the solar system.
Most are less than 1 mm in diameter.
Can be dislodged from comets or broken off of colliding asteroids.

6. Meteor
A meteroid that is pulled into the atmosphere of the earth and burns up.
These meteroids enter the atmosphere of the earth at speeds of 15 km/s to 70 km/s
Meteor shower
Occurs when the Earth passes through the trail of an old comet.
Many meteors occur because of the particles left over from the passing of the comet.

7. Meteorite
A meteor that does not burn up all the way in the atmosphere and ends up hitting the surface of the earth.

8. Asteroids
Fragments of rock made of material similar to the material that formed the planets.
More than 50,000 asteroids have been found in our solar system.

9. Asteroids Asteroid Belt
Area between the orbits of Mars and Jupiter where most asteroids are found.
The asteroid belt extends about 150 million km between the two planets.
Asteroids might exist here because the massive gravity of Jupiter did not allow a planet to form at this position.
Asteroids in the asteroid belt range in size from tiny to 940 km in diameter (an asteroid named Ceres).

10. Asteroids NEAR Near Earth Asteroid Rendezvous
Went into orbit around the asteroid 433 Eros on Feb. 14th, 2000.
Indicates that the asteroid is similar in composition to the most common meteorites that strike the earth and has a surface with many craters.
On Feb 12th, 2001 it became the first spacecraft to land gently on as asteroid.