Vagabonds of the Solar System

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CHAPTER 9 Vagabonds of the Solar System
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WHAT DO YOU THINK?

• Are the asteroids a planet that was somehow
  destroyed?
• How far apart are the asteroids on average?
• Why do comets have tails?
• In which direction does a comets tail point?
• What is a shooting star?

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• You will discover
• that asteroids and meteroids are pieces of
  interplanetary rock and metal
• that comets are bodies containing large amounts
  of ice and rocky debris
• space debris that fall through the Earths
  atmosphere
• that impacts from space have affected past life
  on Earth

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Most asteroids orbit the Sun in the asteroid belt
between the orbits of Mars and Jupiter.
Relative sizes of the Earth, Moon and the
asteroid Ceres
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• Asteroids are classified by their orbits.
• Belt asteroids orbit in the asteroid belt.
• Trojan asteroids orbit the Sun at special points
  in Jupiters orbit.
• Apollo asteroids have highly elliptical orbits in
  the inner solar system.

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Discovering Asteroids Using Time Lapse
Photographs
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Jupiters gravitational attraction produces gaps
(Kirkwood gaps) in the asteroid belt, where the
orbital period of the asteroid is a simple
fraction of Jupiters.
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Close-Up Views of Asteroids Show They Also Have
Impact Craters
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Asteroids also orbit the Sun at Lagrange points,
located 60 ahead and 60 behind Jupiter in its
orbit.
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Highly Elliptical Orbits of the Apollo Asteroids
Cross Earths Path
This asteroid came closer than half the distance
to the Moon.
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MALTHIDE
Near Earth Asteroid Rendezvous
ASTEROID EROS
Looking into a Crater
Just before landing
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Many Objects Exist Far Out in the Solar System
Just outside Plutos orbit is a doughnut-shaped
region of the solar system called the Kuiper
Belt. Beyond this is a spherically-shaped region
called the Oort Cloud, which contains billions of
comets.
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Minor Body Orbits in the Solar System
Because of its size and orbit, some scientists
consider Pluto to be one of the Kuiper Belt
objects instead of a planet.
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Discovery of Kuiper Belt Objects
These white lines show the movement of the Kuiper
Belt objects. There are at least 938 known
objects orbiting in the Kuiper Belt.
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Sedna is the object with the largest known orbit
in our solar system. Its orbit extends outside
the Kuiper belt, approaching the Oort cloud.
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Comets originate from the Far Outer Solar System.
Images of Comet Nuclei
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Comet Kohoutek and Its Hydrogen Envelope
When a comet approaches the Sun, liberated gases
from the surface create a tiny atmosphere called
a coma, as well as a hydrogen envelope that
cannot be seen in visible light.
In visible light
In ultraviolet
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Comets Produce Tails Streaming from the Nucleus
These tails, pushed by the solar wind, point away
from the Sun regardless of the direction the
comet is moving.
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Comets produce two tails, a gas tail (also called
an ion tail), which points directly away from the
Sun, and a dust tail, which curves.
GAS TAIL
DUST TAIL
These images show dramatic changes in the gas
tail, but the dust tail remains the same.
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STRUCTURE OF A COMET
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Comet Brooks had an exceptionally large head.
While Comet Ikeya-Seki has a very small coma, its
tail stretched to a length of more than 1AU.
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Comets are on highly elliptical orbits which, if
undisturbed, will have orbital periods of
hundreds of millions of years. These are called
long-period comets. However, a close encounter
with a large planet can deflect the comet into a
smaller orbit around the Sun. These comets are
called short-period comets.
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Some comets, like Comet Linear, which passed
within 0.74AU of the Sun, fragment into many
pieces.
Comet Hale-Bopp was observed to eject 7 to 10
times more mass than usual during its approach of
the Sun in 1997.
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Meteoroids pulled into our atmosphere by Earths
gravity heat the surrounding gases, causing them
to glow. Thus, they become meteorites.
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During certain predictable times, Earth passes
through sections of its orbit containing debris
from a comet, resulting in a meteor shower.
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Recent Impact Sites on the Moon
On average, 300 tons of mass (the mass of the
obelisk shown above) is added to the Earth from
meteorites each day.
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Different Types of Meteorites
Stony Meteorites
Iron Meteorites
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Stony-Iron Meteorites are the Most Exotic of All
Space Debris Found on Earth
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In 1969, the Allend meteorite created a dazzling
blue display in the skies near Chihuahua, Mexico,
before impact.
SLICED OPEN
The dark blue color is due to carbon in the
meteorite.
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Trees flattened over an area 30km in diameter by
the Tunguska Impact in 1908
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Confirming an Extinction-Level Impact Site
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WHAT DID YOU THINK?

• Are the asteroids a planet that was somehow
  destroyed?
• No. Jupiters gravitational pull prevented
  planets from forming in the asteroid belt, and
  the total mass of the asteroids is much less than
  even that of Pluto.
• How far apart are the asteroids on average?
• 10 million kilometers
• Why do comets have tails?
• Gas and dust evaporate from a comets nucleus,
  and these tails are pushed away from the Sun by
  sunlight and solar wind.
• In which direction does a comets tail point?
• Directly away from the Sun.
• What is a shooting star?
• A piece of space debris plunging through the
  Earths atmosphere.

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Key Terms
amino acid Apollo asteroid asteroid (minor
planet) asteroid belt belt asteroid carbonaceous
chondrite coma (of a comet) comet dust tail (of a
comet) gas (ion) tail hydrogen envelope impact
crater iron meteorite Kirkwood gaps Kuiper
belt long-period comet
meteor meteor shower meteoroid nucleus (of a
comet) Oort cloud radiation (photon)
pressure short-period comet stable Lagrange
points stony meteorite stony-iron meteorite tail
(of a comet) Trojan asteroid Widmanstatten
patterns