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Other Objects in the Solar
System
Chapter 24
Section 4
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.
Comets
• Parts of a comet:
– Head
• Core
– 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.
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.
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.
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.
Meteorite
• A meteor that does not burn up all the way
in the atmosphere and ends up hitting the
surface of the earth.
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.
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).
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.