chapter 8 vagabonds of the solar system. what do you think? were the asteroids a planet that was...
TRANSCRIPT
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Chapter 8 Vagabonds of the Solar System
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What do you think?
• Were the asteroids a planet that was somehow destroyed?
• How far apart are the asteroids on average?
• Why do comets have tails?
• In which direction does a comet tail point?
• What is a shooting star?
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Most asteroids orbit the Sun between Mars and Jupiter
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In general, asteroids are small
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Asteroids are found by looking for moving objects (streaks) in long exposure photographs
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Asteroid Ida and its tiny moon, Dactyl
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A Short History of Asteroids• 1000 km Ceres was discovered in 1801
• 600 km Pallas was discovered in 1802
• Juno and Vesta were discovered in the 19th Century -- all the rest in the 20th Century
• Officially, there are about 7000 known asteroids, most tiny and less than 100 km across, but as many as 100,000 might be out there
• Even 100,000 spread out over an 18,000,000 mile orbit means that they are rather rare
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Was the asteroid belt once a planet that has since been destroyed?
• If all the asteroids were assembled into a planet, it would have a tiny diameter of only 1500 km, or about 12% Earth’s diameter.
• The combination of the pull of the Sun’s gravity and Jupiter’s gravity keeps the asteroids “stirred up” enough to keep anything from coalescing.
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Jupiter’s gravity creates wide
gaps in the
asteroid belt
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Asteroids exist outside the asteroid
belt
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Asteroids exist outside the asteroid belt
• Trojan asteroids in front and behind Jupiter
• Apollo asteroids which cross Earth’s orbit about the Sun
• Kuiper asteroids (Kuiperoids) exist beyond the orbit of Neptune– these Kuiperoids might not be rocky asteroids
at all, but rather, icy comets
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Comets seem to come from two possible places
• Oort Cloud– Reservoir of long period comets that might only
come through the solar system once in billions of years and can come from any direction
• Kuiper Belt– Reservoir of short period comets that come
through the solar system regularly and only come in along the plane of the ecliptic
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The Kuiper Belt of comets spreads from Neptune out 500 AU from the Sun
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Kuiper Belt Object 1993SC - these images were taken 4.6 hours apart
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Comet Kohoutek and Comet West
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Comets lack tails until they enter the inner solar system
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Comets often have two tails:
a thin ION tail and a curving DUST tail
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Anatomy of a comet
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15 km long by 8 km
wideComet Halley nucleus
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Comets don’t last forever
Fragmentation of Comet West shortly after passing near the Sun in 1976
(sequence of photos is from March 8 to March 24)
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Comet orbits are altered by
gravitational interactions with
planets
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Small rocky debris peppers the solar system
• meteors
• falling stars
• shooting stars
• bolides
• fireballseach are caused by small
rocks colliding with Earth’s atmosphere and heating up due to friction with the air
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Meteorites are space debris that land intact
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Meteorite Types
• Stony meteorites – look much like ordinary rocks
• Iron meteorites – heavy and composed on iron and nickel minerals
• Stony-iron meteorites– contain roughly equal amounts of rock and iron– rare ones are carbonaceous chondrites which have
never melted and contain amino acids - one of the building blocks of life
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Impact craters and meteor showers mark remnants of space
debris on Earth
Arizona crater is some 50,000 years old
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The 1908 Siberean Tunguska mystery provides evidence of catastrophic collisions
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A large asteroid’s impact with Earth may well have killed off the dinosaurs
some 65 million years ago
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What did you think?• Were the asteroids a planet that was somehow destroyed?
No, the gravitational pull from Jupiter prevented a planet from ever forming there.
• How far apart are the asteroids on average?The distance between asteroids averages ten million kilometers.
• Why do comets have tails?Gas and dust that evaporate from the comet nucleus are pushed away from the Sun by sunlight
and the solar wind.
• In which direction does a comet tail point?Comet gas tails point directly away from the Sun; comet dust tails make arcs pointing away
from the Sun.
• What is a shooting star? A shooting star is a piece of space debris plunging through the Earth’s atmosphere -- a meteor.
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Self-Check1: Sketch the location of the asteroid belt in the solar system and
explain the nature and origin of the Kirkwood gaps.
2: Describe the relationships among meteoroids, meteorites, meteors, and meteor showers.
3: List the principal classes of meteorites; compare and contrast their compositions and frequencies in space and on Earth.
4: Compare and contrast asteroids, meteoroids, and comets in terms of orbital characteristics, chemical composition, size, and structure.