Chapter 8
By reading this chapter, you will learn
8-1 The key characteristics of the 8-6 Two competing models for the
solar system that must be
origin of the Jovian planets
explained by any theory of its 8-7 How astronomers test the solar
origins
nebula model by observing
8-2 How the abundances of
planets around other stars
chemical elements in the solar
system and beyond explain the
sizes of the planets
8-3 How we can determine the
age of the solar system by
measuring abundances of
radioactive elements
8-4 Why scientists think the Sun
and planets all formed from a
cloud called the solar nebula
8-5 How the solar nebula model
explains the formation of the
terrestrial planets
What triggered the formation of the
solar system?
• Go to: youtube, search for “Birth of the
Solar System” from NationalGeographic
(http://www.youtube.com/watch?v=B1AXbpY
ndGc&feature=related)
Take notes on how the solar system formed.
Formation of
the solar
system
The abundances of the
chemical elements are
the result of cosmic
processes
The vast majority of the atoms in the universe are hydrogen and helium atoms produced
in the Big Bang
Where did all the heavier elements come
from?
1.
2.
3.
Nuclear fusion is a process by which (a)
the nuclei
of lighter elements combine together into heavier
elements. (b) grains of dust and ice collide and stick
together to form the nuclei (inner cores) of
planetesimals. (c) the nuclei of heavier elements split
apart into lighter elements.
The two most common substances in the Universe are
(a)
hydrogen and helium. (b)
hydrogen and
nitrogen. (c) carbon and oxygen.
The fact that all the planets orbit the Sun in the same
direction is strong evidence that a) the solar system
formed from a rotating cloud of gas that collapsed. b) the
planets were formed elsewhere in the Galaxy and were
later captured by the Sun. c) after the planets formed,
collisions between them eventually caused them all to
move in the same direction. d) None of the above. We
do not have any idea yet how our solar system may have
formed.
Click on “enter” to review your answers
1, a, 2. a, 3. a
Nebulosity
• The interstellar
medium is a
tenuous collection of
gas and dust that
pervades the spaces
between the stars
The abundances of radioactive elements reveal
the solar system’s age
• Each type of radioactive nucleus decays at its own
characteristic rate, called its half-life, which can be
measured in the laboratory
• This is the key to a technique called radioactive age
dating, which is used to determine the ages of rocks
• The oldest rocks found anywhere in the solar system
are meteorites, the bits of meteoroids that survive
passing through the Earth’s atmosphere and land on
our planet’s surface
• Radioactive age-dating of meteorites, reveals that they
are all nearly the same age, about 4.56 billion years
old
The Sun and planets • Nebular hypothesis: the solar
formed from a solar nebula system formed from a cloud of
interstellar material called the
solar nebula
• This occurred 4.56 billion years
ago (as determined by
radioactive age-dating)
• The chemical composition; by
mass, 98% H & He and 2%
heavier elements ( where did
these heavier element come from?)
• The nebula flattened into a disk:
Accretion disk
• The Sun formed by gravitational
contraction of the center of the
nebula -> Protosun.
• After about 108 years,
T protosun > 10 million : started H
fusion, became “Sun”.
The planets formed by the
accretion of planetesmals
and the accumulation of
gases in the solar nebula
Formation of the solar system
1. Planetesimals collide and stick together to form protoplanets
because a) of their mutually attractive gravitation. b) they are
weakly charged and can attract each other. c) chemical bonds
hold them together if they happen to collide. d) Both b and c
2. The terrestrial planets formed close to the Sun because a) this
was where most of the silicates in the solar nebula were
located. b) silicates could only condense close to the Sun. c) it
was too hot for the large protoplanets forming here to capture
any significant amounts of hydrogen or helium. d) there was no
hydrogen or helium in the inner solar nebula where these
planets formed.
3. The Jovian planets formed in the outer solar system far from
the Sun because a) this was where most of the hydrogen and
helium in the solar nebula was located. b) there were no
silicates in the outer solar system.c) it was cool enough for the
protoplanets forming here to capture significant amounts of
hydrogen or helium. d) there was no hydrogen or helium in the
inner solar nebula to form Jovian planets.
Click on “enter” to review your answers
1, a, 2. c, 3. c
Astronomers have discovered
planets orbiting
other stars
• Geoff Marcy is using the
10-meter Keck telescope
in Hawaii to measure the
Doppler effect in stars
that wobble because of
planets orbiting around
them
• So far, he and other
teams have found more
than 300 extrasolar
planets
Extrasolar Planets
Most of the extrasolar planets discovered to date are quite massive and
have orbits that are very different from planets in our solar system
•Extra solar planet question:
Extrasolar planets are not seen directly. An observation that has been
used to indirectly show they exist is a) the regular back and forth
movement of the position of spectral lines of the parent stars. b) the
change in luminosity of the parent star when a planet moves in front of
it.c) detection of methane, which can only exist in planetary
atmospheres. d) detection of faint oxygen lines which can only exist in
planetary atmospheres.
Click on “enter” to review your answers
a
Future
plans
SIM PlanetQuest (in the next decade)
The two Terrestrial Planet
will measure the distances and
Finder obs will be detecting and
positions of stars several hundred
characterizing Earth-like up to
times more accurately than any
45 lys away. Atmospheric
previous observations. SIM's precision http://planetquest.jpl.nsignatures (such as H2O, CO2,
will allow us to determine the distances
and O3) of habitable or even
asa.gov/missions/mis
to stars throughout the galaxy and to
inhabited planets.
sions_index.cfm
detect evidence of planets just slightly
larger than Earth.
The Keck Interferometer
combines the light of the
world's largest optical
telescopes to measure
the emission from dust
orbiting nearby stars and
to directly detect and
characterize hot gas
giant planets in other
solar systems.