Chapter 9 Remnants of Rock and Iceascsscience.weebly.com/uploads/3/8/4/1/38417447/asteroid... ·...
Transcript of Chapter 9 Remnants of Rock and Iceascsscience.weebly.com/uploads/3/8/4/1/38417447/asteroid... ·...
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Chapter 9
Remnants of Rock and IceAsteroids, Comets, and Pluto
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9.1 Asteroids and Meteorites
Our Goals for Learning
• Why is there an asteroid belt?
• How are meteorites related to asteroids?
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Asteroid
Facts
• Asteroids are rocky leftovers of planet formation.
• Largest is Ceres, diameter ~1,000 km
• 150,000 in catalogs, and probably over a million with diameter >1 km.
• Small asteroids are more common than large asteroids.
• All the asteroids in the solar system wouldn’t add up to even a small terrestrial planet.
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Asteroids are cratered and not round
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Why is there an asteroid belt?
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More than
150,000
asteroids at
their
predicted
locations for
Jan 1 2004
On this
scale,
asteroids are
much
smaller than
the dots used
to represent
them
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Which explanation seems to be
the most plausible?
A. The belt is where all the asteroids
happened to form.
B. The belt is the remnant of a large
terrestrial planet that used to be between
Mars and Jupiter.
C. The belt is where all the asteroids
happened to survive.
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Which explanation seems to be
the most plausible?
A. The belt is where all the asteroids
happened to form.
B. The belt is the remnant of a large
terrestrial planet that used to be between
Mars and Jupiter.
C. The belt is where all the asteroids
happened to survive. But WHY didn’t they
form a little planet?
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Rocky planetesimals
survived in the asteroid
belt between Mars and
Jupiter because they did
not accrete into a planet.
Jupiter’s gravity, stirs
up the asteroid orbits
and prevents their
planet formation.
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How are meteorites related to
asteroids?
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How are meteorites related to
asteroids?
Meteorites are pieces of asteroids - or
sometimes planets or the Moon.
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Meteor: The bright tail of hot debris from the rock
Meteorite: A rock from space that reaches Earth’s surface
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Peekskill, NY:
October 9, 1992
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Pieces of Asteroids:Meteorite
Types
1) Primitive: Unchanged in composition
since they first formed 4.6 billion years
ago.
2) Processed: Younger, have experienced
processes like volcanism or
differentiation.
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Primitive Meteorites: simple, all
ingredients mixed together
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Processed Meteorites: shattered fragments of larger objects
Iron
from a
core
Volcanic rock from a crust
or mantle
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What do we learn from
meteorites?
• primitive meteorites tell us when solar
system formation began.
• Processed meteorites tell us what asteroids
are like on the inside.
• Processed meteorites provide direct proof
that differentiation and volcanism happened
on asteroids.
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Meteorites from Moon and Mars
• A few meteorites arrive from the Moon and Mars
• Composition differs from the asteroid fragments.
• A cheap (but slow) way to acquire moon rocks and
Mars rocks.
• One Mars meteorite generated a stir when scientists
claimed evidence for microscopic life in it.
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9.2 Comets
• Our Goals for Learning
• How do comets get their tails?
• Where do comets come from?
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How do comets
get their tails?
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Comet Facts
• Formed beyond the frostline, comets are icy counterparts to asteroids.
• “Dirty snowballs” = the nucleus
• Most comets do not have tails.
• Most comets remain perpetually frozen in the outer solar system. Only a few enter the inner solar system, where they can grow tails.
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When a comet nears the Sun, its ices can sublimate into
gas and carry off dust, creating a coma and long tails.
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Draw This
Picture
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Comets eject small particles that follow the comet around
in its orbit
This can cause meteor showers when Earth crosses the
comet’s orbit.
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Meteors in a shower appear to emanate from the same area of sky
because of Earth’s motion through space
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Where do comets come from?
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Kuiper belt:
On orderly orbits
from 30-100 AU in
disk of solar
system
Oort cloud:
On random orbits
extending to about
50,000 AU
Only a tiny number
of comets enter the
inner solar system -
most stay far from
the Sun
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How did they get there?
• Kuiper belt comets align with the plane of
planet orbits
• Oort Cloud Comets were kicked out of the
solar system by the gravity from jovian
planets: random orbits
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9.3 Pluto: Lone Dog
or Part of a Pack?
• Our Goals for Learning
• What is Pluto like?
• Is Pluto a planet or a Kuiper belt comet?
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Pluto: the exception
• Not a gas giant like the other outer planets.
• Has a very elliptical, inclined orbit.
• By far the smallest planet, and smaller than
several moons.
• Has a surprisingly large moon Charon, probably
formed by a huge comet collision with Pluto.
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What is Pluto like?
• 1978 discovery of Pluto’s moon Charon:
Pluto’s mass from Newton’s orbital law.
• It has a thin nitrogen atmosphere that will
refreeze onto the surface as Pluto’s orbit
takes it farther from the Sun.
• Pluto is the largest Solar System object that
has not been visited by spacecraft.
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HST’s view of Pluto & Charon
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Brightness variations during eclipsing orbits showed
dirty ice - like comets.
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Is Pluto a planet or a Kuiper Belt
comet?
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Is Pluto a planet or a Kuiper Belt
comet?
• Pluto is well beyond Neptune, in the Kuiper
Belt.
• Inclined orbit is typical of Kuiper Belt
comets.
• Composition is typical of Kuiper Belt
comets, but not any of the other planets.
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Is Pluto a planet or a Kuiper Belt
comet?
• Kuiper Belt objects have been found that
approach Pluto’s size.
• Kuiper Belt comets have similar orbital
resonances with Neptune.
• Kuiper Belt comets can have moons.
• Triton (a captured moon) is even larger than
Pluto.
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Have we ever witnessed a major
impact?
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Comet SL9 caused a string of
violent impacts on Jupiter in 1994,
reminding us that catastrophic
collisions still happen.
Tidal forces tore it apart during
previous encounter with Jupiter
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Impact plume rises
high above Jupiter’s
surface
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Did an impact kill the dinosaurs?
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Mass Extinctions
• Large dips in total species diversity in the
fossil record.
• The most recent was 65 million years ago,
ending the reign of the dinosaurs.
Was it caused by an impact?
How would it have happened?
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Dinosaur fossils
in lower rock
layers
No dinosaur
fossils in these
rock layers
Thin layer
containing iridium
from impactor
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Iridium - evidence of an impact
• Iridium is very rare in Earth surface rocks
but often found in meteorites.
• Luis and Walter Alvarez found a worldwide
layer containing iridium, laid down 65
million years ago.
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Comet or
asteroid about
10km in
diameter
approaches
Earth
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An iridium-rich
sediment layer and
an impact crater on
the Mexican coast
65 million years
ago.
shows that a large
impact occurred
at the time the
dinosaurs died out,
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The Impact Threat:
Real danger or media hype?
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Facts
• Asteroids and comets have hit the Earth.
• A major impact is only a matter of time: not IF but
WHEN.
• Major impact are very rare.
• Extinction level events ~ millions of years.
• Major damage ~ tens-hundreds of years.
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Tunguska, Siberia: June 30, 1908
The ~40 meter object disintegrated and exploded in the
atmosphere
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Meteor Crater, Arizona: 50,000 years ago (50 meter object)
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Impacts will certainly occur in the future, and while the
chance of a major impact in our lifetimes is small, the
effects could be devastating.
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The asteroid with our name on it
We haven’t seen it yet.
Deflection is more probable with years of advance warning.
Control is critical: breaking a big asteroid into a bunch of little asteroids is unlikely to help.
We get less advance warning of a killer comet…