Chapter 9 Remnants of Rock and Ice Asteroids, Comets, and Pluto

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Chapter 9Remnants of Rock and IceAsteroids,
Comets, and Pluto

• Chapter Outline
• Asteroids and Meteorites
• Comets
• Pluto Lone Dog or Part of a Pack?
• Cosmic Collisions Small Bodies Versus the Planets

Comet Wild 2's Nucleus from Stardust
3/21/2006 1039 AM
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9.1 Asteroids and Meteorites

• 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
• Probably over a million with diameter gt1 km.
• Small asteroids are more common than large
  asteroids.
• All the asteroids in the solar system wouldnt
  add up to even a small terrestrial planet.

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Asteroids Are Cratered and Non-Spherical
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Main Asteroid Belt

• 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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Orbital Resonances With Jupiter
Gravitational interactions (orbital resonances)
with Jupiter have ejected asteroids into certain
orbits specified by the ratio of orbital period
to that for Jupiter.
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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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Meteors and Meteorites
Primitive Meteorite Primitive rocky material
embedded with shiny metal flakes
Stony primitive meteorite
Carbon-rich primitive meteorite
Rocky processed meteorite from asteroid mantle or
crust
Iron processed meteorite from asteroid core
Processed Meteorite Pieces of large asteroids
that underwent chemical differentiation
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9.2 Comets

• How do comets get their tails?
• Where do comets come from?

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Comet Facts

• Formed beyond the frostline, comets are icy
  counterparts to asteroids leftover material.
• 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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Comets Passage by the Sun
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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Anatomy of a Comet
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Comet Approaching the Sun
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Meteor Showers
Comets eject small solid particles that follow
the comet around in its orbit and cause meteor
showers when Earth crosses the comets orbit.
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Dynamics of Meteor Showers
Driving in heavy rain
Earth crossing comet orbit
Meteor shower
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Major Annual Meteor Showers
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Sources of Comets
Only a tiny number of comets enter the inner
solar system - most stay far from the Sun
Oort cloud On random orbits extending to about
50,000 AU
Kuiper belt On orderly orbits from 30-100 AU in
disk of solar system
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9.3 Pluto Lone Dog, or Part of a Pack?

• What is Pluto like?
• Is Pluto a planet or a Kuiper belt comet?

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Pluto will never collide with Neptune because of
a 32 orbital resonance.
Plutos Orbit
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Pluto - The Exception

• Neither a gas giant like the other outer planets
  nor a misplaced terrestrial planet.
• Has a very elliptical, highly inclined, and
  eccentric orbit.
• By far the smallest planet, and smaller than
  several natural satellites.
• Has a surprisingly large satellite Charon,
  probably formed by a huge comet collision with
  Pluto.
• Several objects similar to Pluto found in Kuiper
  Belt.

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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 orbital
  resonances with Neptune.
• Kuiper Belt comets can have moons.
• Triton (a suspected captured moon) is even larger
  than Pluto.

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9.4 Cosmic Collisions Small Bodies Versus the
Planets

• 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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Crater Chain on Callisto
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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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Comet Shoemaker-Levy 9 Impacting Jupiter
Infrared
Visible
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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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65 Million Year Old Sediment Layer
No dinosaur fossils in these rock layers
Thin layer containing iridium from impactor
Dinosaur fossils in lower rock layers
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Iridium Probable 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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Yucatan Impact
An iridium-rich sediment layer and an impact
crater on the Mexican coast show that a large
impact occurred at the time the dinosaurs died
out, 65 million years ago.
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Yucatan Impact Responsible for Extinction of
Dinosaurs
Responsible for world-wide habitat change leading
to extinction of the dinosaurs
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Size and Impact Frequency
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Jovian Planets Influence on Earth Impacts
Jovian planets determine where asteroids and
comets are today. They might protect Earth from
most of bombardment.
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The Big Picture

• The smallest bodies in the solar systemasteroids
  and cometsare our best evidence of how the solar
  system formed.
• The small bodies are subjected to the
  gravitational whims of the planets, particularly
  the Jovian planets. The subtleties of resonances
  play a major role in sculpting the outer solar
  system.
• The interplay of large and small bodies brings us
  meteorites to teach us our origins, comets and
  meteor showers to light up the sky, and impacts
  that can alter or obliterate life as we know it.
• Pluto is called the ninth planet, but it bears
  much more similarity to the thousands of
  Kuiper-belt comets than to the other eight
  planets.