Download Asteroids and Meteors

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Lecture 17
Asteroids and Meteors
January 8b, 2014
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Asteroids
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Bodies of rock (some iron)
Irregular shape
Typically 0.1 - 600 km
Total number of visible asteroids may be
100,000.
• Detected by movement with respect to stars.
• Average distance between asteroids
~1,000,000 km
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Path of Asteroid
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Toutatis -- Radar Image
Size:
4.6 × 2.4 × 1.9 km
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Vesta -- HST Image
Diameter:
530 km
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Orbits of Asteroids
• Most orbit Sun in Asteroid Belt between Mars
and Jupiter
• Debris that was not able to form a planet due
to pull from Jupiter.
• Apollo Asteroids
– high orbital eccentricities.
– Cross the orbit of the Earth
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Resonances (optional material)
• Jupiter’s pull disrupts orbits of some
asteroids.
• Trojan asteroids -- share orbit with Jupiter.
• Kirkwood gaps
– orbits in the asteroid belt where few asteroids
are found.
– Orbits correspond to fraction of Jupiter’s
period.
– Continual tug of Jupiter when it lines up with
asteroids in same place in their orbit pulls them
to a different orbit.
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Gaspra and Ida
• Two asteroids observed by Galileo on the
way to Jupiter.
• Irregular shape.
• Many craters.
• Ida has its own “moon”
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Gaspra -- Galileo Image
Size: 19 x
12 x 11 km
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Ida and Dactyl -- Galileo Image
Size: 58 x 23 km
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Eros -- NEAR Image
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Meteoroids
• Meteoroids -- small debris in space, usually
< 100 m in diameter
• Meteor -- meteoroid falling through Earth’s
atmosphere.
– Friction with air causes it to heat and burn up.
– Seen as “shooting star”
– Most burn completely, only largest make it to
the Earth
• Meteorite -- meteoroid that makes it to the
surface of the Earth.
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Meteor Showers
Quadrantids
Date of Maximum
intensity
January 3
Lyrids
April 22
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Lyra
Eta Aquarids
May 4
20
Aquarius
Delta Aquarids
July 30
20
Aquarius
Perseids
August 12
80
Perseus
Orionids
October 21
20
Orion
Taurids
November 4
15
Taurus
Leonids
November 16
15
Leo Major
Geminids
December 13
50
Gemini
Ursids
December 22
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Ursa Major
Shower
Typical
Constellation
hourly rate
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Boötes
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Meteor Showers
• Some cometary
orbits cross orbit of
the Earth.
• When they break up
they leave debris in
orbit.
• Earth passes through
debris, many
meteors are seen.
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Meteor Shower
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Meteorites
Iron
Stony-Iron
Stony
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Earth Impacts
• Earth is continually being bombarded.
Barringer Meteor Crater, Arizona
Diameter: 1.2 km
Age: ~50,000 years
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Tunguska Event -- Siberia (1908)
• Asteroid
destroyed in
atmosphere.
• Leveled trees
for over 20 km
from
explosion.
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Chicxulub Crater -- Yucatan
Peninsula, Mexico
• Dinosaurs -- possibly destroyed by asteroid
impact ~65 million years ago
– Alvarez & Alvarez found iridium rich layer of
clay
Chicxulub
Diameter ~170 km
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Risks of Impact
20m
Diameter
200m
2km
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© The New Yorker Collection 1998 Frank Cotham from cartoonbank.com. All Rights Reserved