Remnants of Rock and Ice

1

• Remnants of Rock and Ice

• Asteroids
• Meteoroids (meteorites, meteor)
• Comets

2
Remnants of the Solar Nebula

• Small bodies remain virtually unchanged since
  their formation 4.5 billion years ago
• They carry history of the Solar system in their
  compositions, locations, and numbers.

Asteroid means starlike, a rocky
leftover Meteoroid small rocky material in
space Meteor in the atmosphere (falling
star) Meteorite any piece of rock than fell to
the ground from the sky Comet means hair (Greek),
an icy leftover
3
Asteroids (minor planets)

• Most abundant between the orbits of Mars and
  Jupiter
• Largest is Ceres, 800 km diameter
• Most are much smaller, irregular

4
Asteroids
The first asteroid Ceres was discovered by
Piazzi on January 1, 1801 in an attempt to find
the missing planet between Mars and
Jupiter Ceres has a diameter of half of
Pluto There are more than 100,000 asteroids
larger than 1 km in diameter
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Asteroid Eros
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Asteroids (minor planets)
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Evolution of the Belt
Early in the history of the Solar system, the
belt contained enough planetesimals to form a
planet.
Gravitational tugs from Jupiter created the gaps.
Two stable zones along Jupiters orbit host two
families of asteroids (Trojans).
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Jupiters Trojan Asteroids
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Meteorites
Meteorites are pieces of rock that fell from the
sky. Seen as fireballs (sometimes with
sound) May cause damage, but most fall into
oceans
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Meteorites
Meteor showers result of the Earths passing
through a comet orbit Meteors are single pieces
of comet dust 25 million meteoroids enter
Earths atmosphere every day Meteor showers get
their names after constellations from which they
appear to radiate
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Meteor
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Meteor Showers
(These occur when earth passes through cloud of
debris along a comets orbit.)
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Leonid Meteor Shower
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Meteor Trail Recorded During Leonid Meteor
Shower, 1998
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Ionized Trail Generation by Meteor Crossing
Eastern US, 1992
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The Origin of Meteorites
Primitive meteorites may be either rocky or
carbon-rich
Processed meteorites can be removed from the
surface of a planet by an impact. There are
meteorites from Moon and Mars found on Earth.
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Primitive Meteorites
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Processed Meteorites
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Comets

• Chunks of rock and ice in highly eccentric orbits
• Near sun, ice evaporates to produce tail
• A couple have been visited by robotic craft

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Comet Structure
Comets are basically dirty snowballs where ice
mixes with rocky dust. Their mean size is a few
kilometers across.
The comet body is called nucleus. Sublimating
ices create coma. A tail pointing away from the
Sun appears. There are two tails plasma tail and
dust tail.
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Nucleus of Comet Borrelli
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Comets
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Comet Orbits
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Comets
Comets contain information about the outer solar
system Most of them visit the inner part only
once, a few are regular guests
One of the most famous comets is Halleys comet.
It was discovered by Edmund Halley in 1682. Its
orbital period is 76 years. The last appearance
in 1986.
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Halleys Comet
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Comet Halley
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Comet Hale-Bopp
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Comet Hale-Bopp
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Sun Grazing Comets
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Comet Shoemaker-Shoemaker-Levy 9
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Earth impacts

• Do we ever get hit?
• Yes! The questions are when and by what?
• Classify events by size
• Small
• Medium
• Large

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Impacts
The larger the impactor, the more rare the impact
In 1908, an unusual explosion occurred in
Siberia. Meteor crater in Arizona formed 50,000
years ago. A large impact occurred 65 million
years ago perhaps caused the dinosaur extinction.
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Earth impacts small

• Small less than 50 m across at top of atmosphere
• Happening all the time
• Will burn up or break up in the atmosphere
• Most are very tiny (pea sized)
• Meteors! (Shooting stars, Falling stars)
• Can see 3 - 5 per hour on a typical night
• 25 million every day!
• 100 tons per day

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Earth impacts medium

• Medium 50 m - 1 km across at top of atmosphere
• Only one every century or millennium
• Causes severe local damage
• Two great examples from recent history

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Earth impacts medium

• The Tunguska event - Siberia, Russia
• Happened in 1908
• Flattened a forest
• Knocked people over 200 km (140 miles) away
• No crater (exploded just above ground)
• The impactor?
• A stony meteorite (?) Size 30 m across

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The Tunguska event
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The Tunguska event
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Earth impacts medium

• The Berringer Crater, in Arizona
• Happened 50,000 years ago
• The crater
• 1,200 m across
• 200 m deep

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Earth impacts medium

• The impactor?
• An iron meteorite
• 100 m across (50 m on impact)
• Going 40,000 mph!
• Explosion 20 million tons of TNT
• A moderate atomic bomb
• 2 Mt. Saint Helens

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The Berringer crater, Arizona
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Meteor Crater in Arizona
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Earth impacts large

• Large more than 1 km across at top of atmosphere
• One every few million years
• Severe global effects
• More than 2 km can cause mass extinction
• Most recent 65 million years ago

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Earth impacts large

• The K/T extinction event
• Some history
• K/T Cretaceous / Tertiary
• 60 of all species on Earth disappeared,
  including the dinosaurs
• One explanation (there are several) Earth was
  hit by a large impactor

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Earth impacts large

• The K/T extinction event
• Evidence for an impact
• Iridium found at that geologic level
• A crater near the Yucatan, in Mexico

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The K/Textinctionevent
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Earth impacts large

• The K/T extinction event
• The impactor
• Probably a comet
• Size 10 km across
• Energy released
• 100 million million tons of TNT
• 5 million atomic bombs
• 10 million Mt. Saint Helens

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How often is there an impacted?
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How often do impacts occur?
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• http//astro1.panet.utoledo.edu/anatoly/astr1010/
  materials/324,41,Slide 41
• http//campus.pari.edu/sara/arecibo/presentations/
  fields/294,13,Meteor Trail Recorded During
  Leonid Meteor Shower, 1998
• http//departments.weber.edu/physics/schroeder/ast
  ro/lectureslides/356,8,Kuiper Belt objects (other
  stuff near Pluto)
• http//www.phys-astro.sonoma.edu/people/faculty/ca
  rico/A100/367,2,Earth impacts