Transcript Universe 8e Lecture Chapter 8 Origin of Our Solar System

Roger A. Freedman • William J. Kaufmann III
Universe
Eighth Edition
CHAPTER 8
Comparative Planetology II
The Origin of Our Solar System
HW – Chapter 8 Online Quiz due Monday 10/11
By reading this chapter, you will learn
8-1 The key characteristics of the 8-5 How the solar nebula
solar system that must be
model explains the
explained by any theory of its
formation of the terrestrial
origins
planets
8-2 How the abundances of
chemical elements in the solar 8-6 Two competing models
for the origin of the Jovian
system and beyond explain
planets
the sizes of the planets
8-3 How we can determine the
8-7 How astronomers test the
age of the solar system by
solar nebula model by
measuring abundances of
observing planets around
radioactive elements
other stars
8-4 Why scientists think the Sun
and planets all formed from a
cloud called the solar nebula
A.Overestimate of
the true age
B. Underestimate
of the true age
Key Ideas
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Models of Solar System Formation: The most
successful model of the origin of the solar system is
called the nebular hypothesis. According to this
hypothesis, the solar system formed from a cloud of
interstellar material called the solar nebula.
This occurred 4.56 billion years ago (as determined by
radioactive dating).
Key Ideas


The Solar Nebula and Its Evolution: The chemical
composition of the solar nebula, by mass, was 98%
hydrogen and helium (elements that formed shortly after
the beginning of the universe) and 2% heavier elements
(produced much later in the centers of stars, and cast
into space when the stars died).
The heavier elements were in the form of ice and dust
particles.
Key Ideas
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Formation of the Planets and Sun: The terrestrial
planets, the Jovian planets, and the Sun followed
different pathways to formation.
The four terrestrial planets formed through the accretion
of dust particles into planetesimals, then into larger
protoplanets.
In the core accretion model, the four Jovian planets
began as rocky protoplanetary cores, similar in character
to the terrestrial planets. Gas then accreted onto these
cores in a runaway fashion.
Key Ideas
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In the alternative disk instability model, the Jovian
planets formed directly from the gases of the solar
nebula. In this model the cores formed from
planetesimals falling into the planets.
The Sun formed by gravitational contraction of the center
of the nebula. After about 108 years, temperatures at the
protosun’s center became high enough to ignite nuclear
reactions that convert hydrogen into helium, thus forming
a true star.
Key Ideas
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Extrasolar Planets: Astronomers have discovered
planets orbiting other stars.
Most of these planets are detected by the “wobble” of the
stars around which they orbit.
A small but growing number of extrasolar planets have
been discovered by the transit method, by microlensing,
and direct imaging.
Most of the extrasolar planets discovered to date are
quite massive and have orbits that are very different from
planets in our solar system.