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Solar System Solar System DebrisDebris
Asteroids, Comets, Meteors, Oh My!
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Asteroids• Asteroids are small,
irregular, rocky bodies that orbit the sun
• Most are located between he orbits of Mars and Jupiter in the asteroid belt
• Some are located in the same orbit as Jupiter, but are separated by 60º - Trojans
• Some asteroids are in highly elliptical orbits that pass earth – Earth-crossing asteroids, Near-earth asteroids (NEAs), Near-earth objects (NEOs)
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What do asteroids look like?
• Too small to be seen with the naked eye – need large telescopes
• Appear as streaks because of their motion
• Three fly-bys of asteroids:– Gaspra by Galileo in 1998– Ida by Galileo in ????– Mathilde by NEAR in 1999
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What are asteroids made of?• Asteroids are classified into a number of types
according to their spectra (and hence their chemical composition) and albedo:1. C-type, includes more than 75% of known
asteroids:– extremely dark (albedo 0.03)– approximately the same chemical
composition as the Sun minus hydrogen, helium and other volatiles
2. S-type, 17%– relatively bright (albedo .10-.22)– metallic nickel-iron mixed with iron- and
magnesium-silicates3. M-type, most of the rest
– bright (albedo .10-.18)– pure nickel-iron
4. There are also a dozen or so other rare types
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Asteroids
• How many are there?– Some 5000 with
well-determined orbits– Probably >500,000 larger
than 1 km
• How big are they?– Largest (Ceres) is 940 km in diameter– Three larger than 500 km– About a dozen larger than 250 km– Number increases rapidly with decreasing
size
• Total mass of all asteroids ~ 5% of the moon
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Comets• Comets are small
bodies of ice and dust that form tails as they near the sun.
• What way is this comet moving?
• Recall Kepler’s second law. Where do comets spend most of their time?
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What are comets made of?
• When they are near the Sun and active, comets have several distinct parts: – nucleus: relatively solid and stable,
mostly ice and gas with a small amount of dust and other solids;
– coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus;
– hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen;
– dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye;
– ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.
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Where do comets live?
• Short period comets come from the Kuiper belt
• Long period comets from the Oort cloud
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What happens when comets loose their
tails?• Meteor showers
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MeteoritesThree main types:• Stony
– Look like ordinary earth rocks at first glance. If you were to look closely, you would see that the outsides of the rocks look melted. Most meteorites (93%) striking the earth are stony
• Irons– These dark grey, metallic, and very
dense meteorites are unlike any earth rocks that you have ever seen. Five percent of meteorites striking the earth are irons
• Stony-Irons– These meteorites have clumps of both iron
and stone
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Asteroid – Meteorite Connection
• Iron– similar to type M asteroids
• Stony Iron– like type S asteroids
• Stony– Chondrite
• by far the largest number of meteorites fall into this class;similar in composition to the mantles and crusts of the terrestrial planets
– Carbonaceous Chondrite• similar to type C asteroids
– Achondrite• similar to terrestrial basalts
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Finding Meteorites
• Finds– Found on earth, often long after they landed– usually noticed because of their unusual appearance
or their unusual location
• Falls– These meteorites are seen falling, making a fireball
in the sky. By following the trail, the landing site and meteorite can be found. Most of these are stony meteorites
Peekskill, NY 1994
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Impacts
• What happens when a meteor hits the ground?– Usually
nothing– Occasionally,
large pieces make it to the ground and create impact craters
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Impact Hazards• No person has ever been killed by a
meteorite hitting earth• However, a large impact killed the
dinosaurs• A smaller impact in remote Russia in 1908
knocked down trees and could have caused severe damage in a populated area
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Earth Sterilizing Impact
Mass Extinction Impact
Civilization Threatening Impact
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Terrestrial Impact Frequency
year
century
million yr.
billion yr.
ten thousand yr.
100 millionmillion10,00010010.01
Hiroshima
Tunguska
K/T
TNT equivalent yield (MT)
Global catastrophe
Tsunami danger