Universe Tenth Edition Chapter 15 Vagabonds of the Solar System Roger Freedman Robert Geller William Kaufmann III

Comet Hale-Bopp, the Great Comet of 1997

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 By reading this chapter, you will learn

Ceres Compared with Earth and Moon

The Trail of an Asteroid 15-1: A search for a planet between Mars and Jupiter led to the discovery of asteroids

The Asteroid Belt

The Kirkwood Gaps 15-2: Jupiter’s gravity helped shaped the asteroid belt

The Kirkwood Gaps

A Hubble Space Telescope View of a Large Asteroid

A Radar View of a Medium-Sized Asteroid 15-3: Astronomers use a variety of techniques to study asteroids

A Spacecraft View of a Small Asteroid

Sample Returned from Itokawa

Vesta

Impact on Vesta

An Asteroid with Two Satellites

Asteroid Collisions

Asteroids Outside the Belt

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

A Meteor

A Meteorite “Fender Bender”

Stony Meteorites 15-5: Meteorites are classified as stones, stony irons or irons depending on their composition

Stony Meteorites

A Stony Iron Meteorite

Iron Meteorites

A Piece of the Allende Meteorite 15-6: Some meteorites retrain traces of the early solar system

Comet Hyakutake 15-7: A comet is a chunk of ice and dust that partially vaporizes as it passes near the Sun

The Structure of a Comet

Comet Nuclei and Jets

Comet Wild 2

Comet Tempel 1

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

The Kuiper Belt and the Oort Cloud 15-8: Comets originate either from the Kuiper belt or from the Oort Cloud

Transforming a Comet Orbit

The Fragmentation of Comets

Comet Shoemaker-9 and Its Encounter with Jupiter

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.