Asteroid, Meteor, Comets
Transcript of Asteroid, Meteor, Comets
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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 wouldnt add up toeven 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
theirpredicted
locations for
Jan 1 2004
On this
scale,
asteroids are
muchsmaller than
the dots used
to represent
them
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Why are there very few asteroids
beyond Jupiters orbit?
A. There was no rocky material beyond Jupiters
orbit.B. The heaviest rocks sank towards the center of the
solar system.
C. Ice could form in the outer solar system.
D. A passing star probably stripped away all ofthose asteroids, even if they were there at onetime.
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Why are there very few asteroids
beyond Jupiters orbit?
A. There was no rocky material beyond Jupiters
orbit.B. The heaviest rocks sank towards the center of the
solar system.
C. Ice could form in the outer solar system.
D. A passing star probably stripped away all ofthose asteroids, even if they were there at onetime.
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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 asteroidshappened 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 asteroidshappened to survive. But WHY didnt they
form a little planet?
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Rocky planetesimals
survived in the asteroid
belt between Mars andJupiter because they did
not accrete into a planet.
Jupiters 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 - orsometimes 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 Earths surface
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Peekskill, NY:
October 9, 1992
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Pieces of Asteroids:Meteorite
Types1) Primitive: Unchanged in composition
since they first formed 4.6 billion years
ago.
2) Processed: Younger, have experienced
processes like volcanism ordifferentiation.
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Primitive Meteorites: simple, all
ingredients mixed together
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Processed Meteorites:
shattered fragments of larger objects
Iron
from acore
Volcanic rock from a cru
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 asteroidsare like on the inside.
Processed meteorites provide direct proof
that differentiation and volcanism happenedon 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 andMars rocks.
One Mars meteorite generated a stir when scientists
claimed evidence for microscopic life in it.
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What have we learned? Why is there an asteroid belt?
Orbital resonances with Jupiterdisrupted the orbits of
planetesimals, preventing them
from accreting into a planet.
Those that were not ejected
from this region make up the
asteroid belt today. Most
asteroids in other regions of the
inner solar system accreted into
one of the planets.
How are meteorites related toasteroids?
Most meteorites are pieces of
asteroids. Primitive meteoritesare essentially unchanged sincethe birth of the solar system.Processed meteorites arefragments of larger asteroids
that underwent differentiation.
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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 icycounterparts 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 theinner solar system, where they can growtails.
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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
comets orbit.
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Meteors in a shower appear to emanate from the same area of skybecause of Earths 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 orbitsextending to about
50,000 AU
Only a tiny number
of comets enter the
inner solar system -
most stay far fromthe 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 thesolar system by the gravity from jovian
planets: random orbits
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What have we learned? How do comets get their tails?
The vast majority of comets donot have tails. Only those fewcomets that enter the solarsystem grow tails. As the cometapproaches the Sun its nucleusheats up. Some of the cometsice sublimates into gas, and theescaping gases carry alongsome dust. The gas and dustform a coma and two tails: a
plasma tail of ionized gas and adust tail. Larger particles canalso escape, becoming theparticles that cause meteors andmeteor showers on Earth.
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What have we learned? Where do comets come from?
Comets that enter the solarsystem come from one of tworeservoirs in the outer solarsystem: the Kuiper belt and theOort cloud. The Kuiper belt
comets still reside in the regionbeyond Neptune in which theyformed during the birth of thesolar system. The Oort cloudcomets are thought to have
formed in the region of thejovian planets, and were kickedout to the great distance of theOort cloud by gravitationalencounters with the planets.
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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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Pluto will never collide with Neptune because
of a 3:2 orbital resonance.
http://orbits_neptune_pluto.htm/ -
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What is Pluto like?
1978 discovery of Plutos moon Charon:
Plutos mass from Newtons orbital law.
It has a thin nitrogen atmosphere that willrefreeze onto the surface as Plutos orbit
takes it farther from the Sun.
Pluto is the largest Solar System object thathas not been visited by spacecraft.
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HSTs 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 Beltcomets.
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 Plutos size.
Kuiper Belt comets have similar orbitalresonances with Neptune.
Kuiper Belt comets can have moons.
Triton (a captured moon) is even larger thanPluto.
What have we learned?
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What have we learned? What is Pluto like?
Pluto is much smaller than
any other planet, with an orbitmore elliptical and moreinclined to the ecliptic planethan that of any other planet.It is made mostly of ices andhas a very thin atmosphere ofgases that are expected tofreeze onto the surface asPluto moves farther from the
Sun in its 248-year orbit. Ithas a moon, Charon, with aslightly lower density thanPluto, suggesting that Charonmay have been formed in a
giant impact.
Is Pluto a planet or a Kuiper
belt comet?
Whether Pluto should be
called a planet is a matter
of opinion, but its properties
suggest that it is a Kuiper belt
comet. Its composition andorbital properties match those
of other Kuiper belt comets
and do not fit in with the
other planets. It is the largest
known Kuiper belt comet
today, but there may be larger
ones still awaiting discovery.
9 4 C i C lli i ll
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9.4 Cosmic Collisions: small
bodies vs. the planets
Our Goals for Learning
Have we ever witnessed a major impact?
Did an impact kill the dinosaurs?
Is the impact threat a real danger or just media
hype?
How do other planets affect impact rates and life
on Earth?
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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 Jupiters
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 rocklayers
No dinosaur
fossils in theserock layers
Thin layer
containing iridiumfrom 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 worldwidelayer 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 onthe Mexican coast
65 million years
ago.
shows that a largeimpact 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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An object 1km in size would produce a mile-high tidal wave
This slide is placeholder in case you would like to
download and show the movie noted below (notes
field).
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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 havent 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 killercomet
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What are we doing about it?
Stay tuned to
http://impact.arc.nasa.gov
http://impact.arc.nasa.gov/http://impact.arc.nasa.gov/ -
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How do other planets
affect impact ratesand life on Earth?
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Gravity from
Jovial planets
can influencethe path of
comets and
Asteroids.
They couldprotect us or
steer one in
our direction
Fig 9.20
W J it f lif
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Was Jupiter necessary for life
on Earth?
Impacts can extinguish
life.
But were they
necessary for life as
we know it?
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What have we learned? Have we ever witnessed
a major impact? In 1994, we observed
the impacts of comet
ShoemakerLevy 9 on
Jupiter. The comet had
fragmented into a string
of individual nuclei, so
there was a string of
impacts that left
Jupiters atmosphere
scarred for months
What have we learned?
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What have we learned? Did an impact kill the
dinosaurs? We are not certain whether animpact was the sole cause, buta major impact clearlycoincided with the mass
extinction in which thedinosaurs died out, about 65million years ago. Sedimentsfrom the time show clearevidence of an impact, and an
impact crater of the right agehas been found near the coastof Mexico.
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What have we learned?
Is the impact threat a
real danger or just
media hype?
Impacts certainly posea threat, though the
probability of a major
impact in our lifetimes
is fairly low.
What have we learned?
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What have we learned?
How do other planets affect impact rates and lifeon Earth?
Impacts of asteroids and comets are always linked in at
least some way to the gravitational influences of
Jupiter and the other jovian planets. Thesegravitational influences have shaped the asteroid belt,
the Kuiper belt, and the Oort cloud, and sometimes
still help determine when an object is flung our way.