Meteorites, Asteroids, and Comets

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Meteorites, Asteroids, and Comets
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Please pick up your transmitter and swipe your ID
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Meteorites
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• 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

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Which one of those objects would appear as a
shooting star?

1. Only meteoroids.
2. Only meteors.
3. Only meteorites.
4. Meteors and meteoroids.
5. Meteors and meteorites.
6. Meteoroids and meteorites.
7. All three.

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Meteorites
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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).
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Meteor Showers
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Most meteors appear in showers, peaking
periodically at specific dates of the year.
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Meteoroid Orbits

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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.
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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.
2. The tracks should all be parallel.
3. The tracks should all appear to come from the
   same point in space.
4. The tracks should all appear to move toward the
   same point in space.

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Radiants of Meteor Showers
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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
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The Leonid Meteor Shower in 2002
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Would you expect a meteor shower to be equally
intense each year?

1. Yes, because all the meteors should orbit the sun
   in about 1 year, so there should be no
   fluctuations from year to year.
2. Yes, because the meteors are evenly distributed
   over the entire former comet orbit.
3. 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.
4. No. In fact, they should only be visible in one
   year at all.

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Meteorite Impacts on Earth
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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
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The Origins of Meteorites
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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
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Asteroids
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Last remains of planetesimals that built the
planets 4.6 billion years ago!
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Where do we find most asteroids in the solar
system?

1. In a belt between the Earth and Mars.
2. In a belt between Mars and Jupiter.
3. In a belt far outside the orbits of the planets.
4. On highly elliptical orbits, coming as close to
   the sun as Mercurys orbit, and reaching as far
   out as Plutos orbit or beyond.
5. In elliptical orbits around Jupiter.

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The Asteroid Belt
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Most asteroids orbit the sun in a wide zone
between the orbits of Mars and Jupiter.
Mars
Jupiter
Pluto
Uranus
Saturn
Neptune
(Distances and times reproduced to scale)
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The Asteroid Belt
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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
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What causes the divisions (e.g., Cassini
Division) in the rings of Saturn?

1. Orbital resonances with moons orbiting Saturn
   outside the ring system.
2. Material close to an orbit of a moon inside the
   ring system being swept up by the moon.
3. Random fluctuations causing some regions around
   Saturn to be empty.
4. Orbital resonances with moons orbiting Saturn
   inside the ring system.

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Kirkwood Gaps
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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 23 resonance
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Non-Belt Asteroids
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Not all asteroids orbit within the asteroid belt.
Apollo-Amor Objects
Trojans Sharing stable orbits along the orbit
of Jupiter.
Asteroids with elliptical orbits, reaching into
the inner solar system.
Some potentially colliding with Mars or Earth.
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Comets
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Comet Ikeya-Seki in the dawn sky in 1965
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Throughout history, comets have been considered
as portants of doom, even until very recently
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Appearances of comet Kohoutek (1973), Halley
(1986), and Hale-Bopp (1997) caused great concern
among superstitious.
Comet Hyakutake in 1996
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Where on its orbit does a comet spend most of its
time?
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2

1. 1
2. 2
3. 3
4. 4

4
1
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Two Types of Tails
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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
suns radiation pressure. Lagging behind the
comet along its trajectory
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Enter question text...
Where is the sun with respect to this comet?

1. 1
2. 2
3. 3
4. 4
5. 5

2)
3)
1)
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4)
5)
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Gas and Dust Tails of Comet Mrkos in 1957
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Comet Hale-Bopp in 1997
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Fragmentation of Comet Nuclei
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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 Earths moon and
on Jupiters moon Callisto may have been caused
by fragments of a comet.
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Fragmenting Comets
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Comet Linear apparently completely vaporized
during its sun passage in 2000.
Only small rocky fragments remained.
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The fragments of a comet can produce a new

1. Moon of Jupiter.
2. Moon of Mars.
3. Planet.
4. Meteor shower.
5. Group of asteroids.

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The Geology of Comet Nuclei
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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
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The Deep Impact Mission
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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
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The Origin of Comets
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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.
40,000 100,000 AU
Interactions with planets may perturb orbits
further, capturing comets in short-period orbits.
Oort Cloud
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The Kuiper Belt
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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.
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Beyond the Solar System
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