Transcript Remnants of Rock and Ice - Physics & Astronomy | SFASU

Remnants of Rock and Ice:
Asteroids, Comets, and Pluto
Remnants of Rock and Ice
Remnants
Birth
• Comets,
Asteroids andfrom
Meteorites
carry the
history of our solar system encoded in their
compositions, locations, and numbers.
• Asteroid:
– a rocky leftover planetesimal orbiting the Sun.
• Comet:
– an icy leftover planetesimal orbiting the Sunregardless of its size or whether or not it has a tail.
• Meteor:
– a flash of light in the sky caused by a
particle entering the atmosphere, whether
the particle comes from an asteroid or a
comet.
• Meteorite:
– any piece of rock that fell to the ground from
the sky, whether from an asteroid, a comet,
or even another planet.
Asteroids
• The main Asteroid Belt lies between 2.2
and 3.3 AU from the Sun.
• Origin and Evolution of the Asteroid
belt:
– The Asteroid belt probably formed as a result of orbital
resonance. Resonance occurs whenever one object’s
orbital period is a simple ratio of another object’s
period.
– These resonances with Jupiter probably prevented a
planet from ever forming in the region of the Asteroid
Belt.
• Another effect of the resonance is to form gaps
in the orbits of the Asteroids as they orbit the
Sun.
• These are called the Kirkwood Gaps.
The Kirkwood Gaps
Asteroids are recognizable in
telescope images because they move
relative to the stars in just a short
time.
See SFA Observatory
SFA Observatory Asteroid
Discoveries
Gaspra (16 km across) Galileo
Ida(53 km) and its
tiny moon Galileo
Mathide(59 km)
NEAR
Eros (40 km) NEAR
Meteorites
• Primitive Meteorites: Most primitive
meteorites are composed of rocky
minerals with an important difference
from Earth rocks.
• The Primitive Meteorites are our best
source of information about conditions
in the solar nebula.
Processed Meteorites
• A smaller group of meteorites appears
to have undergone substantial change
since the formation of the solar system.
• These “Processed Meteorites”
apparently were once part of a larger
object that modified the original
material into another form.
Carbon-rich primitive
meteorite
Primitive
Stony primitive meteorite
Differential iron
meteorite
Differential stony
meteorite
Processed
Origin of Meteorites
• Carbon –rich meteorites came from the
outer portion of the asteroid belt.
(> 3AU)
• Carbon – poor meteorites formed in the
inner warmer part of the asteroid belt.
• The processed meteorites have
compositions similar to the cores,
mantles, or crusts of the terrestrial
worlds. These are fragments of the
terrestrial worlds.
• Processed meteorites with
basaltic compositions must have
come from lava flows.
Comets
• Icy Planetesimals that have been left over
from the formation of the Solar System.
“Sun Grazing” comet observed by The
Solar and Heliospheric Observatory
(SOHO).
Anatomy of a Comet
Comets exist as bare nuclei
over most of their orbits
and grow a coma and tails
only when they approach
the Sun
The
Kuiper
Belt and
the Oort
Cloud
Pluto
• Pluto was discovered in 1930 by an American
Astronomer named Clyde Tombaugh.
• Pluto has long been seen to be a misfit among
the planets, fitting into neither the terrestrail
nor the jovian category.
• It has a 248 year orbit that is unusually
elliptical and significantly tilted relative to the
ecliptic.
• Pluto has a moon – Charon.
Cosmic Collisions
• The numbers of small bodies
orbiting the solar system have
diminished significantly since the
days of early bombardment, when
most impact craters were formed.
• However, there are still plenty of
fragments left and collisions between
these fragments and the planets still
occur on occasion.
Comet
Shoemaker
-Levy 9
Comet Shoemaker-Levy 9
The End.
Comet Shoemaker-Levy 9
• Was shatter by Jupiter’s gravity in 1992.
• All pieces hit Jupiter in the summer of 1994
leaving dark impact scars.
Images obtained by Dan Bruton in 1994
Meteor Shower
Minor Body Comparisons
Property
___Asteroids
_________ Comets
Orbit Shape
Circular to
elliptical
Highly
elliptical
Size
0.5 km to 625 km
Nucleus
1 to 10 km
Composition
Named?
Iron or Rocky
Named by their
discoverers
Ice and Rock
Named after their
discoverers
Earth Impacts and Near Misses
• Arizona Meteor Crater
– measures 1 mile across
– from an impact 50,000 years ago
– by a 50 meter meteoroid
• Tunguska Event
– in 1908
– an asteroid broke up in our atmosphere
– leveled trees for some 30 kilometers
Frequency of Impacts versus impactor size & Effects
• Chicxulub Event /cheek-shoo-loob/
– 65,000,000 years ago
– 10 kilometer asteroid
– is thought to have caused a mass extinction of
dinosaurs
The End...
Live long and prosper.