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Meteorites, Asteroids,
and Comets
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Meteorites
• Meteoroid = small body in space
Distinguish
between:
• Meteor = meteoroid colliding with Earth and
producing a visible light trace in the sky
• Meteorite = meteor that survives the plunge
through the atmosphere to strike the ground
Which one of those objects would
appear as a “shooting star”?
1.
2.
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7.
:10
Only meteoroids.
Only meteors.
Only meteorites.
Meteors and meteoroids.
Meteors and meteorites.
Meteoroids and meteorites.
All three.
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Meteorites
Sizes from microscopic dust to a few centimeters.
About 2 meteorites
large enough to
produce visible
impacts strike the
Earth every day.
Statistically, one
meteorite is expected to
strike a building
somewhere on Earth
every 16 months.
Typically impact onto the atmosphere with 10 – 30 km/s
(≈ 30 times faster than a rifle bullet).
Meteor Showers
Most meteors appear in showers, peaking
periodically at specific dates of the year.
Meteoroid Orbits
Meteoroids contributing
to a meteor shower are
debris particles, orbiting
in the path of a comet.
Spread out all along the
orbit of the comet.
Comet may still exist or
have been destroyed.
Only few sporadic meteors are not associated with comet orbits.
What kind of pattern would you expect to see,
comparing the tracks of various meteors of one shower?
1.
The tracks should have random
directions.
The tracks should all be parallel.
The tracks should all appear to
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come from the same point in space.
The tracks should all appear to
move toward the same point in
space.
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25%
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Radiants of Meteor Showers
Tracing the tracks of meteors in a shower backwards,
they appear to come from a common origin, the radiant.
↔ Common
direction of
motion
through
space.
The Perseid Meteor Shower
The Leonid Meteor
Shower in 2002
Would you expect a meteor shower
to be equally intense each year?
1.
:10
Yes, because all the meteors should orbit the
sun in about 1 year, so there should be no
fluctuations from year to year.
Yes, because the meteors are evenly
distributed over the entire former comet orbit.
25%
No, because the meteors should be
concentrated around the former location of the
comet, which orbited around the sun with a
longer period than 1 year.
No. In fact, they should only be visible in one
year at all.
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Meteorite Impacts on Earth
Over 150 impact craters found on Earth.
Famous
example:
Barringer
Crater near
Flagstaff, AZ:
Formed ~ 50,000 years ago by a
meteorite of ~ 80 – 100 m diameter
The Origins of
Meteorites
Planetesimals cool and differentiate;
Collisions eject material from
different depths with different
compositions and temperatures.
Meteorites can not have been broken
up from planetesimals very long ago
→ Remains of planetesimals
should still exist.
→ Asteroids
Asteroids
Last remains of
planetesimals
that built the
planets 4.6
billion years
ago!
Where do we find most
asteroids in the solar system?
1.
2.
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In a belt between the Earth and Mars.
In a belt between Mars and Jupiter.
20%
In a belt far outside the orbits of the
planets.
On highly elliptical orbits, coming as
close to the sun as Mercury’s orbit,
and reaching as far out as Pluto’s orbit
or beyond.
In elliptical orbits around Jupiter.
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The Asteroid Belt
Most asteroids
orbit the sun in a
wide zone
between the
orbits of Mars
and Jupiter.
(Distances and times reproduced to scale)
The Asteroid Belt
Small, irregular
objects, mostly in the
apparent gap
between the orbits of
Mars and Jupiter.
Thousands of
asteroids with
accurately
determined orbits
are known today.
Sizes and shapes of the largest
asteroids, compared to the moon
What causes the divisions (e.g., Cassini
Division) in the rings of Saturn?
1.
Orbital resonances with moons orbiting
Saturn outside the ring system.
Material close to an orbit of a moon
inside the ring system being swept up by
the moon.
Random fluctuations causing some
regions around Saturn to be empty.
Orbital resonances with moons orbiting
Saturn inside the ring system.
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Kirkwood Gaps
The asteroid orbits are not evenly distributed throughout
the asteroid belt between Mars and Jupiter.
There are several gaps where no asteroids are found:
Kirkwood gaps
These correspond
to resonances of
the orbits with the
orbit of Jupiter.
Example:
2:3 resonance
Non-Belt Asteroids
Not all asteroids orbit within the asteroid belt.
Apollo-Amor
Objects:
Asteroids
with elliptical
orbits,
reaching into
the inner
solar system.
Some
potentially
colliding with
Mars or Earth.
Trojans:
Sharing stable
orbits along
the orbit of
Jupiter.
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Comets
Comet Ikeya-Seki in
the dawn sky in 1965
Throughout history, comets have been considered
as portants of doom, even until very recently:
Appearances of comet Kohoutek (1973), Halley
(1986), and Hale-Bopp (1997) caused great concern
among superstitious.
Comet Hyakutake in 1996
3
Where on its
orbit does a
comet spend
most of its
time?
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Two Types of Tails
Ion tail: Ionized gas
pushed away from the
comet by the solar wind.
Pointing straight away
from the sun.
Dust tail: Dust set free
from vaporizing ice in
the comet; carried away
from the comet by the
sun’s radiation pressure.
Lagging behind the
comet along its
trajectory
Where is the sun
Enter
with respect
to
this comet?
question text...
20%2) 20%
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Gas and Dust Tails of
Comet Mrkos in 1957
Comet HaleBopp in 1997
Fragmentation of Comet Nuclei
Comet nuclei are very fragile and are easily fragmented.
Animation 1
Animation 2
Comet Shoemaker-Levy was disrupted by tidal forces of Jupiter
Two chains of impact
craters on Earth’s
moon and on Jupiter’s
moon Callisto may
have been caused by
fragments of a comet.
Fragmenting Comets
Comet Linear
apparently completely
vaporized during its
sun passage in 2000.
Only small rocky
fragments remained.
The fragments of a comet can
produce a new …
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Moon of Jupiter.
Moon of Mars.
Planet.
Meteor shower.
Group of asteroids.
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The Geology of Comet Nuclei
Comet nuclei contain ices of water, carbon dioxide, methane, ammonia, etc.
(Materials that should have condensed from the outer solar nebula).
Not solid ice
balls, but fluffy
material with
significant
amounts of
empty space.
“Dirty
snowballs”
The Deep Impact Mission
Video 1
Video 2
Placing a probe into the path of Comet Tempel 1
and documenting the result of the impact
Impact: July 4, 2005
The Origin of Comets
Comets are believed to originate in the Oort cloud:
Spherical cloud of several trillion icy bodies,
~ 10,000 – 100,000 AU from the sun.
Gravitational influence
of occasional passing
stars may perturb some
orbits and draw them
towards the inner solar
system.
Oort Cloud
Interactions with
planets may perturb
orbits further,
capturing comets in
short-period orbits.
The Kuiper Belt
Second source of small, icy bodies in the outer solar system:
Kuiper Belt, at
~ 30 – 100 AU
from the sun.
Pluto and Charon
may be captured
Kuiper-Belt objects.
Beyond the Solar System