Asteroids
Printable
version
April
6, 2000
Announcements
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Quiz
#2 in discussion section next week
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Covers
Chapters 18.1-18.6, 10,11,12
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Homework
5 due next Tuesday
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Observing
project:
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Daylight
savings time this past weekend
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Next
Honors section:
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THIS
Wed April 5 (weather permitting) at 8:00 pm
Asteroids
Preview
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Discovery
of asteroids
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Naming
convention
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Distribution
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Up
close and personal
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When
astroids land on Earth
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Types
of metorites
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The
big one
Discovery
of Asteroids
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Gap
in planets between Mars and Jupiter
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Missing
planet?
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No,
asteroids
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In
late 1700's, search for planet
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German
"Celestial Police"
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Sicilian
Giuseppe Piazzi beat them to it
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Had
been looking at stars
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saw
one move over the course of a few days
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Called
it Ceres after patron goddess of Sicily
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Ceres
is the largest asteroid but not the missing planet
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minor
planet
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P =
4.6 years
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a =
2.77 AU
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r =
918 km
Early
Asteroid Work
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Second astreroid discovered
1802 by Heinrich Olbers
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Juno 1804
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Vesta 1807
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A couple 100 by mid 1800s
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Max Wolf 1891 started using
photographs
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asteroids leave streaks
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discovered 228 asteroids
Naming
Asteroids
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If you discover an asteroid,
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First you get a provisional
name, e.g.: 2000 GA
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2000 Year
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G for first half of April,
B would be second half of Jan
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A for first one discovered
in that time period
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If it is seen again on four
successive opositions, it is real
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You get an official number
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You get to name it
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1 Ceres
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2 Palas ...
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3834 Zappafrank (found in
1980)
Distribution
of Asteroids
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Most
asteroids found between Mars and Jupiter
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Once
though to be remenant of "missing planet"
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Probably
just left over from formation of solar system
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All
asteroids put together would be only 1500 km in diameter
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Computer
simulations: Jupiter influcenced formation of asteroid belt
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without
Jupiter, another Earth-sized planet may have formed
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Jupiter's
gravity disrupts orbits, throws asteroids out if they get to close
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crack
the whip phenomenon
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A Mars-sized
planet may have formed
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kicked
1862 Apollo, 1566 Icarus out of belt but not out of solar system
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What
happened to Mars-sized object?
Lagrange
and Kirkwood
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In 1772 Joseph Louis Lagrange
predicted special stable points at intervals around a planet's orbit
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In 1906 clumps of asteroids
were discovered at Jupiter's L4 and L5
points.
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In 1867 Daniel Kirkwood discovered
gaps in the asteroid belt
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P2 = a3
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Gaps in distance (a) correspond
to gaps in period (P)
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Gaps in period are simple
fractions of Jupiter's period
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e.g. 1/3
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asteroids with these orbits
are disturbed so much, they get kicked out of the solar system
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WHY?
Asteroids
up close and personal
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Asteroids are less than 1000
km wide
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There is an average of 106
km between asteroids
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space probes don't need to
worry about hitting asteroids
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More asteroids earlier in
history of solar system, lots of time
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Ateroids to collide
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Chunks stay around in Hirayama
families
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To get a good view of an
asteroid, you have to visit
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Rotate every 5-20 hours
Ida and its mini moon
Eros
Asteroids
hitting the Earth
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Small
asteroids are called Meteroids
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If
they make it to Earth they usually burn up in the atmosphere
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Meteors
that land on the ground are called Meteorites
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Result
of impact is usually an impact crater
Barringer
Crater, Arizona
Types
of Meteorites
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Stony
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rock
+ small amounts of iron
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Stony
Iron
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rock
+ large amounts of iron
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Iron
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Widmanstatten
Patterns
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Iron
that cools over a long period of time
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Carbonaceuos
Chondrite
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source
of organic compounds
Stony
Stony
Iron
Iron
Widmanstatten
paterns in iron meteorite
Carbonaceuos
Chondrite
The
BIG ONE
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Layer
of iridium clay around world deposited 65 million years ago
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Many
iron meteorites contain irridium
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2/3
of all living species became extinct 65 million years ago
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A very
large meteorite may have struck the near the Yucatan peninsula
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impact
may have kicked up dust that obscured the sun
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plants
died
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large,
cold blooded animals died
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mammals
survived
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Can
it happen again?
Irridium
rich clay
Asteroids
Summary
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Discovery
of asteroids
-
Naming
convention
-
Distribution
-
Up
close and personal
-
When
astroids land on Earth
-
Types
of metorites
-
The
big one