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Comets,
Asteroids, and
Meteors
Comets
• The word "comet" comes from the Greek
word, kome for "hair”. Kometes means
“long-haired star”
• Our ancestors thought comets were stars
with what looked like flowing hair trailing
behind.
Comets: “Dirty Snowballs”
• Comets are loose collections of ice, dust,
and small rocky particles whose orbits are
usually very long, narrow ellipses.
Structure of a Comet
A Comet’s Head
– Outer layer= Coma (water vapor,
CO2, and other gases)
– Solid inner core= Nucleus (frozen
ice, gas and dust )
Structure of a Comet
Ion Tail
Dust
Tail
Coma
To Sun
Comet’s Tail
• As a comet approaches the sun and heats
up, some of its gas and dust stream outward,
forming a tail.
• Most comets have 2 tails:
– gas (ion), tail
– dust tail
• Tails point away from the sun because of
the force of the solar wind.
• A comet’s tail can be more than 100 million
kilometers long.
Comet’s Tail
Comet’s Orbit
• Comets move in an elliptical shaped orbit.
Origin of Comets
• Most comets are found in 2 regions of the
solar system: Kuiper belt and Oort cloud.
• Kuiper belt-doughnut-shaped region that
extends beyond Neptune’s orbit to about
100 times Earth’s distance from the sun.
• Oort cloud-spherical region of comets that
surrounds the solar system out to more than
1,000 times the distance between Pluto and
the sun.
The Oort Cloud
 In
1950 Jan Oort noticed that
 no
comet has been observed with an orbit that
indicates that it came from interstellar space,
 there
is a strong tendency for aphelia of long period
comet orbits to lie at a distance of about 50,000 AU,
and
 there
is no preferential direction from which comets
come.
The Oort Cloud
Famous Comets
• Comet Halley is perhaps the most famous comet
in history.
• Each time this comet's orbit approaches the Sun,
its 15-km (9-mile) nucleus sheds about 6 m (7
yards) of ice and rock into space. This debris
forms an orbiting trail that, when falling to Earth,
is called the Orionids meteor shower.
• Halley’s comet reappears every 76 years. Its next
appearance is in 2061.
Comet Halley
Bayeaux Tapestry
Norman Invasion of 1066
Comet Hale-Bopp
• July 23, 1995- an
unusually large and bright
comet was seen outside of
Jupiter's orbit by Alan
Hale of New Mexico and
Thomas Bopp of Arizona.
• Exceptionally large size.
• It was visible even
through bright city skies,
and may have been the
most viewed comet in
recorded history.
• It will not appear again for
another 2,400 years.
Hale-Bopp
Other Famous Comets
• Comet Hyakutake-On January 30, 1996, Yuji Hyakutake
(pronounced "hyah-koo-tah-kay"), an amateur astronomer
from southern Japan, discovered a new comet using a pair
of binoculars.
• Comet Shoemaker-Levy 9-Between July 16 and July 22,
1994, more than 20 fragments of Comet Shoemaker-Levy
9 collided with the planet Jupiter. Astronomers Carolyn
and Eugene Shoemaker and David Levy discovered the
comet in 1993. It was the first collision of two Solar
System bodies ever to be recorded.
Comet Exploration
• The Deep Impact spacecraft was launched
in December 2004 and encountered comet
Tempel 1 on July 4, 2005-mission that
studied and impacted comet Tempel 1.
• http://spaceplace.jpl.nasa.gov/en/kids/deepi
mpact/index.shtml#air
• Click on image in center of page to see
animation
Asteroids
• A rocky space object.
• Large range of sizes, but are usually larger
than meteoroids.
• Most asteroids are found in the asteroid
belt.
• The asteroid belt is located between the
orbits of Mars and Jupiter.
How many asteroids are there?
• There are about 40,000 known asteroids that are
over 0.5 miles (1 km) in diameter in the asteroid
belt About 3,000 asteroids have been cataloged.
• There are many smaller asteroids (100,000).
• Asteroids are made of metals, silicate, iron, nickel,
and carbon.
• The first one discovered (and the biggest) is
named Ceres; it was discovered in 1801.
• Asteroids range in size from tiny pebbles to about
578 miles (930 kilometers) in diameter (Ceres).
ASTEROIDS BECOMING MOONS
• Asteroids can be pulled out of their solar
orbit by the gravitational pull of a planet.
They would then orbit that planet instead of
orbiting the Sun.
• Astronomers theorize that the two moons of
Mars, Phobos and Deimos, are captured
asteroids.
Asteroid Strike
• Scientists hypothesize that a large asteroid
hit Earth 65 million years ago and caused
extinction of many animal species on
Earth, including the dinosaurs.
• Scientists also hypothesize that the largest
mass extinction, 250 million years ago,
killing off 90% of all species was also
caused by a large asteroid.
Asteroid Exploration
• Near Earth Asteroid Rendezvous- (NEAR)
mission is the first of NASA's Discovery missions
and the first mission ever to go into orbit around
an asteroid (launched 1996).
• Studies were made of the asteroid Eros’ size,
shape, mass, magnetic field, composition, and
surface and internal structure (last data signals
sent in 2001)
Meteoroids
• Meteoroid- small chunk of rock or dust in
space.
• Meteoroids come from comets or asteroids.
Meteor
• When a meteoroid enters Earth’s atmosphere,
friction with the air creates heat and produces a
streak of light that you can see in the sky.
• A meteor is the streak of light that is produced
when a meteoroid enters Earth’s atmosphere and
burns up.
• A meteor shower occurs when many meteors can
be seen over a short period of time.
The Cause of Meteor Showers
Meteorites
• Meteoroids that pass through the
atmosphere and hit Earth’s surface are
called meteorites.
• Classified by composition: stony, iron ,or
stony-iron.
Near Earth Objects (NEO)
What can we do if a large comet, meteoroid or
asteroid is in Earth’s path?
• Unknown… Still experimenting with ideas.
• Scientist are calculating ways to use nuclear
energy to divert an incoming object.
• High energy x-ray pulses produce a shock
wave to push the NEO in the opposite
direction.