Transcript What are Asteroids, Meteors and Comets? How are they similar

Small Bodies In Space:
Asteroids, Comets
and Meteors
Small Bodies in Space?
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Besides the sun, 8 planets and their moons there
are also:
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Asteroids
Comets
Meteors
…or space leftovers?!
Asteroids
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Asteroid: A rocky object in space that can be a
few feet wide to several hundred miles wide.
Asteroids are fragile, inactive objects
Majority orbit the sun
Are found in the asteroid belt between the orbits
of Mars and Jupiter
Asteroids: Size
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Range in size: from 1 km across to over 100 km
across
The first and largest asteroid Ceres; was
discovered in 1801
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933 km in diameter
The smallest asteroid 1991 BA was discovered in
1991
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6 meters across
Asteroids: Composition
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Astronomers classify asteroids based on what
they are made of:
Carbon
 Minerals
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Asteroids: Measurement
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In 1991 the USA created and launched the first
space probe for close range observation of
asteroids
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Named Galileo
First asteroid photographed; Gaspra
Asteroids: Measurement
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In 1996 National Aeronautics and Space
Administration (NASA) launched the probe
NEAR (Near Earth Asteroid Rendezvous)
Flew by Mathilde in 1997
Flew by Eros in 1998
Landed on Eros in 2001
In 2000 it was renamed NEAR-Shoemaker after
an American Astronomer
Asteroids: Orbit
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Orbit: the path a moon, planet, or small body in
space takes as it travels around another body in
space
Most follow an oval-shaped orbit in the asteroid
belt
Asteroids: Orbit
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Some follow orbits outside the asteroid belt and
follow the same orbit as Jupiter; known as
Trojans
Some asteroids are known as near-Earth
asteroids, they orbit in the inner solar system
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Can cross the orbital path of Mars and Earth
Asteroids: Collisions with Earth
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Many scientists believe that a near-Earth
Asteroid collided with Earth around 65 million
years ago, which triggered global environmental
changes that led to the extinction of the
dinosaurs.
Asteroids: Gravitational Force
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The gravitational pull from Jupiter and other large
planets causes asteroid orbits to slowly change
Orbital changes can lead asteroids to collide with one
another; increasing the likelihood of further collisions
Collisions create smaller asteroids and fragments.
Some small fragments reach the earths surface as
meteorites.
Group Discussion
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Why are there asteroids between Mars and
Jupiter instead of a planet?
Why do you think the asteroid belt is located
where it is?
Do you think that there is a high or low
probability that the Earth will be hit by another
large asteroid? Why?
Comets: Dirty Snowballs from Space
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Comet: A small object made up of ice, dust and
gas that orbit the sun. Jets of gas and dust form
long tails that reflect sunlight and can be seen
from Earth
Consist of a solid nucleus core that is
surrounded by a cloudy atmosphere called a
coma and has one or two tails
Comets are usually only seen through a
telescope
Comets:
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Astronomers believe that comets are the left
over debris from 4.6 billion years ago when the
outer planets were first formed
Comets: Classification
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Astronomers classify comets according to how
long they take to orbit the sun
Short-Period comets need less than 200 years to
complete one orbit
 Long-Period comets takes 200 years or more to
complete one orbit
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Comets: The Kuiper Belt
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Scientists think that short-period comets come
from a band of objects called the Kuiper belt;
which lies beyond the orbit of Pluto
Within the Kuiper belt comets are inactive
The gravitational pull of the outer planets can
shift objects out of the Kuiper belt and into the
inner solar system where they become active
comets
Comets: The Oort Cloud
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Long-period comets come from the Oort cloud;
a nearly spherical collection of icy bodies about
1,000 times farther away from the sun than
Pluto
Within the Oort cloud comets are inactive
Gravitational interactions with passing stars can
cause the icy bodies in the Oort cloud to enter
the inner solar system and become active comets
Comets
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Comets move in long, oval shaped orbits that
can cross the almost circular orbit of the
planets.
Sometimes comets collide with planets and their
moons; the majority of impact craters across the
galaxy are a result of comet collisions
Comets: Life
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Comets lose ice and dust each time they return to the
inner solar system; leaving behind trails of dusty debris
When Earth travel through on of these trails the debris
become meteors that burn up into the Earths
atmosphere.
Eventually a comet will lose all of its ice, it will then
break up and dissipate into clouds of dust or turn into
fragile, inactive objects (similar to asteroids)
Comets: Halley’s Comet
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Originally discovered in 1682 by Sir Edmund
Halley
Passes earth every 76 years
Most famous comet
When it passed near Earth in 1986, five
spacecraft flew past the comet and gathered
information about its appearance and chemical
composition
Group Discussion
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If Halley was discovered in 1782, and Halley
takes 76 years to orbit the sun, roughly when
will Halley pass earth again? How old will you
be?
Do you think there will be visible differences in
Halley’s comet the next time it appears? What
differences would you expect to see?
How many more times do you predict Halley
will pass by earth again? Why?
ANSWER
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The next time the Halley comet will pass earth
will be in 2062
Meteors:
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Meteor: Appear when a chunk of metallic or
stony matter called a meteoroid enters the
Earths atmosphere from outer space
A bright streak of light that appears briefly in
the sky: can be seen with the unaided eye
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Often called falling/shooting stars
Meteoroids come from broken, disintegrated
pieces of comets and asteroids
Meteors
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Air friction heats up the meteoroid chunk and
causes it to glow and create a shining trail of
gases and melted particles
Most glow for about a second,
Most disintegrate long before touching the
Earths surface
Meteoroids that reach the Earths surface are
called meteorites
Meteors
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Millions of meteors occur in the Earths
atmosphere every day – most are no bigger than
a pebble
Meteoroids travel around the sun in a variety of
orbit shapes and velocities
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Fastest ones move 42 km per second
Meteors
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The earth encounters a number of streams (trails) or
swarms (clusters) of tiny meteoroids at certain times of
the year.
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Streams and swarms have oval-shaped orbits like comets
The most brilliant meteor shower took place in
November 12-13 1833. Since then this meteor shower
continues to take place every November and seems to
come from the direction of the constellation Leo
(Leonid Shower)
Meteors: Types
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There are three kinds of meteors:
Stony: consist of minerals rich in silicon and oxygen
and come from the outer crust of a comet/asteroid
 Iron: consist mostly of iron and nickel and comes
from the metallic core of a comet/asteroid
 Stony-iron: Consists of equal amounts of
silicon/oxygen and iron/nickel and come from the
inner crust of a comet/asteroid
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Meteors: Size
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Meteor size varies; most are relatively small
Larger bodies like asteroids and comets can also strike
the earth and become meteorites.
Meteors will only strike the earth surface when they are
just the right size, if they are too small they disintegrate
into the atmosphere, if they are too big they will often
explode when they hit the atmosphere – raining down
much smaller pieces
Thousands of small meteorites have been found in
Antarctica, which have provided scientists with clues to
the types of materials that form planets
Meteors: Impact Craters
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Scientists have found more than 120 impact
craters/basins on earth from meteors, comets,
asteroids.
Most famous: Meteor Crater in Arizona
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1, 275 meters across and 175 meters deep
Formed nearly 50, 000 years ago when an iron meteorite
weighing 330, 000 metric tons struck the Earth
Most impact points larger than the meteor crater have
been worn away by time and surface changes
Group Discussion
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Why do people confuse a falling meteor with a
falling star?
When you think about or see a falling meteor
how does it make you feel?
Do you really think it is possible to know what
small body a meteor came from?