Roger Freedman • Robert Geller • William Kaufmann III
Universe
Tenth Edition
Chapter 15
Vagabonds of the Solar System
Comet Hale-Bopp, the Great Comet of 1997
By reading this chapter, you will learn
• 15-1 What led to the
discovery of the asteroids
• 15-2 Why the asteroids
never formed into a planet
• 15-3 What asteroids look
like
• 15-4 How an asteroid led to
the demise of the dinosaurs
• 15-5 What meteorites tell
us about the nature of
asteroids
• 15-6 What meteorites may
reveal about the origin of
the solar system
• 15-7 What comets are and
why they have tails
• 15-8 How comets originate
from the outer solar system
Ceres Compared with Earth and Moon
15-1: A search for a planet between Mars and
Jupiter led to the discovery of asteroids
The Trail of an Asteroid
The Asteroid Belt
The Asteroid Belt
15-2: Jupiter’s gravity helped shaped the asteroid belt
The Kirkwood Gaps
The Kirkwood Gaps
A Hubble Space Telescope View of a Large Asteroid
15-3: Astronomers use a variety of
techniques to study asteroids
A Radar View of a Medium-Sized Asteroid
A Spacecraft View of a Small Asteroid
Sample Returned from Itokawa
Vesta
Impact on Vesta
Impact on Vesta
An Asteroid with Two Satellites
Asteroid Collisions
Asteroid Collisions
Asteroids Outside the
15-4: Asteroids are found outside the
asteroid belt – and have struck Earth
The Barringer Crater
Iridium-Rich Clay
Confirming an Extinction-Level Impact Site
Aftermath of the Tunguska Event
Russian Asteroid Impact of 2013
Russian Asteroid Impact of 2013
Russian Asteroid Impact of 2013
A Meteor
A Meteorite
“Fender Bender”
15-5: Meteorites are classified as stones, stony
irons or irons depending on their composition
Stony Meteorites
Stony Meteorites
Stony Meteorites
A Stony Iron Meteorite
Iron Meteorites
Iron Meteorites
Iron Meteorites
15-6: Some meteorites retrain traces of
the early solar system
A Piece of the Allende Meteorite
15-7: A comet is a chunk of ice and dust that
partially vaporizes as it passes near the Sun
Comet Hyakutake
The Structure of a Comet
Comet Nuclei and Jets
Comet Nuclei and Jets
Comet Wild 2
Comet Wild 2
Comet Wild 2
Comet Tempel
A Comet and Its Hydrogen Envelope
A Comet and Its Hydrogen Envelope
The Orbit and Tail of a Comet
The Two Tails of Comet Hale-Bopp
The Antitail of Comet Hale-Bopp
Comet Halley’s Eccentric Orbit
15-8: Comets originate either from the Kuiper
belt or from the Oort Cloud
The Kuiper Belt
and the Oort
Transforming a Comet Orbit
Transforming a Comet Orbit
The Fragmentation of Comets
The Fragmentation of Comets
Comet Shoemaker-9 and
Its Encounter with Jupiter
Meteoritic Storms
Meteoritic Storms
Asteroid 243 Ida and Its Tiny Moon Dactyl
Key Ideas
•
Discovery of the Asteroids: Astronomers first discovered the asteroids while
searching for a “missing planet.”
•
Thousands of asteroids with diameters ranging from a few kilometers up to
1000 kilometers orbit within the asteroid belt between the orbits of Mars and
Jupiter.
•
Origin of the Asteroids: The asteroids are the relics of planetesimals that
failed to accrete into a full-sized planet, thanks to the effects of Jupiter and
other Mars-sized objects.
•
Even today, gravitational perturbations by Jupiter deplete certain orbits
within the asteroid belt. The resulting gaps, called Kirkwood gaps, occur at
simple fractions of Jupiter’s orbital period.
•
Jupiter’s gravity also captures asteroids in two locations, called Lagrangian
points, along Jupiter’s orbit.
Key Ideas
• Asteroid Collisions: Asteroids undergo collisions with each other,
causing them to break up into smaller fragments.
• Some asteroids, called near-Earth objects, move in elliptical orbits
that cross the orbits of Mars and Earth. If such an asteroid strikes
the Earth, it forms an impact crater whose diameter depends on
both the mass and the speed of the asteroid.
• An asteroid struck the Earth 65 million years ago, possibly causing
the extinction of the dinosaurs and many other species.
Key Ideas
•
Meteoroids, Meteors, and Meteorites: Small rocks in space are called
meteoroids. If a meteoroid enters the Earth’s atmosphere, it produces a
bright trail called a meteor (or shooting star). A rock that does not burn up in
the atmosphere and reaches Earth’s surface is called a meteorite; most of the
meteoroids are too small to make it to Earth before becoming completely
vaporized.
•
Meteorites are grouped into three major classes, according to composition:
iron, stony iron, and stony meteorites. Irons and stony irons are fragments of
the core of an asteroid that was large enough and hot enough to have
undergone chemical differentiation, just like a terrestrial planet. Some stony
meteorites come from the crust of such differentiated meteorites, while
others are fragments of small asteroids that never underwent differentiation.
Key Ideas
• Rare stony meteorites called carbonaceous chondrites may
be relatively unmodified material from the solar nebula.
These meteorites often contain organic material and may
have played a role in the origin of life on Earth.
• Analysis of isotopes in certain meteorites suggests that a
nearby supernova may have triggered the formation of the
solar system 4.56 billion years ago.
Key Ideas
• Comets: A comet is a chunk of ice with embedded rock fragments
that generally moves in a highly elliptical orbit about the Sun.
• As a comet approaches the Sun, its icy nucleus develops a
luminous coma, surrounded by a vast hydrogen envelope. An ion
tail and a dust tail extend from the comet, pushed away from the
Sun by the solar wind and radiation pressure, respectively.
• Origin and Fate of Comets: Comets are thought to originate from
two regions, the Kuiper belt and the Oort cloud.
Key Ideas
• The Kuiper belt lies in the plane of the ecliptic at distances between 30
and 50 AU from the Sun. Its icy objects are thought to be the source of
short-period comets, whose periods are less than 200 years.
• The Oort cloud is thought to contain billions of icy objects in a
spherical distribution that extends out to 50,000 AU from the Sun. The
long period comets, with periods greater than 200 years are thought
to originate in the Oort cloud.
• Fragments of “burned out” comets produce meteoritic swarms. A
meteor shower is seen when the Earth passes through a meteoritic
swarm.