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

The Origin of Our
Solar System II
By reading this unit, you will answer the
following questions…
What are the key characteristics of the
solar system that must be explained by
any theory of its origins?
 How do the abundances of chemical
elements in the solar system and beyond
explain the sizes of the planets?
 How we can determine the age of the
solar system by measuring abundances
of radioactive elements?
 Why do scientists think the Sun and
planets all formed from a cloud called the
solar nebula?

By reading this unit, you will answer the
following questions…
How does the solar nebula model explains
the formation of the terrestrial planets?
 What are the two competing models for
the origin of the Jovian planets?
 What are extrasolar planets and how are
they detected?
 How do astronomers test the solar nebula
model by observing extrasolar planets
around other stars?

The Solar Nebular Theory
Interstellar Cloud (Nebula)
Gravitational Collapse
Protosun
Heating  Fusion
Sun
Leftover Materials
Asteroids
Protoplanetary Disk
Condensation (gasliquidsolid)
Metal, Rocks
Gases, Ice
Accretion
Nebular
Capture
Terrestrial
Planets
Jovian
Planets
(depends on temperature)
Leftover Materials
Comets
Major Physical Processes in Solar
Nebular Theory
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Heating
 Protosun  Sun
-In-falling materials converts gravitational energy into
thermal energy (heat)  Kelvin- Helmholtz contraction
-The dense materials collides with each other, causing the
gas to heat up.
-Once the temperature and density gets high enough for
nuclear fusion to start, a star is born.
Major Physical Processes in Solar
Nebular Theory

Spinning  Smoothing of the
random motions
-Conservation of angular momentum causes
the in-falling material to spin faster and
faster as they get closer to the center of the
collapsing cloud.
Major Physical Processes in Solar
Nebular Theory

Flattening  Protoplanetary disk.
-The solar nebula flattened into a disk.
-Collision between clumps of material turns
the random, chaotic motion into a orderly
rotating disk.
Major Physical Processes in Solar
Nebular Theory

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Heating
Spinning
Flattening
This process explains the orderly motion
of most of the solar system objects!
Core Accretion Model for Jovian
Planet Formation
 Initially
core of Jovian planets formed
by accretion of solid materials
 Then,
gas accreted onto solid core to
form gas giant
Disk Instability Model for Jovian
Planet Formation
 Gases
rapidly accrete and condense
to form Jovian planets without a solid
core
Extrasolar Planets
An extrasolar planet,
or exoplanet, is a
planet beyond our solar
system, orbiting a star
other than our Sun
Types of Extrasolar Planets
Hot Jupiter
A type of extrasolar planet whose mass is close to or exceeds
that of Jupiter (1.9 × 1027 kg), but unlike in the Solar System,
where Jupiter orbits at 5 AU, hot Jupiters orbit within
approximately 0.05 AU of their parent stars (about one eighth
the distance that Mercury orbits the Sun)
Example: 51 Pegasi b
Types of Extrasolar Planets
Pulsar Planet
A type of extrasolar planet that is found orbiting pulsars, or
rapidly rotating neutron stars
Example: PSR B1257+12 in the constellation Virgo
Types of Extrasolar Planets
Gas Giant
A type of extrasolar planet with similar mass to Jupiter and
composed on gases
Example: 79 Ceti b
Types of Extrasolar Planets
-A super-Earth is an extrasolar planet with a
mass higher than Earth's, but substantially below
the mass of the Solar System's gas giants.
-term super-Earth refers only to the mass of the
planet, and does not imply anything about the
surface conditions or habitability. The alternative
term "gas dwarf" may be more accurate
OGLE-2005-BLG-390Lb
Types of Extrasolar Planets
A hot Neptune is an extrasolar planet in an
orbit close to its star (normally less than one
astronomical unit away), with a mass similar
to that of Uranus or Neptune

Gliese 581 b
Methods of Detecting Extrasolar
Planets
Transit Method
•If a planet crosses ( or
transits) in front of its parent
star's disk, then the observed
visual brightness of the star
drops a small amount.
•The amount the star dims
depends on the relative sizes
of the star and the planet.
Methods of Detecting Extrasolar
Planets
Astrometry
•This method consists of precisely
measuring a star's position in the
sky and observing how that position
changes over time.
•If the star has a planet, then the
gravitational influence of the planet
will cause the star itself to move in a
tiny circular or elliptical orbit.
•If the star is large enough, a
‘wobble’ will be detected.
Methods of Detecting Extrasolar
Planets
Doppler Shift (Radial Velocity)
•A star with a planet will
move in its own small orbit in
response to the planet's
gravity. The goal now is to
measure variations in the
speed with which the star
moves toward or away from
Earth.
•In other words, the
variations are in the radial
velocity of the star with
respect to Earth. The radial
velocity can be deduced
from the displacement in the
parent star's spectral lines
(think ROYGBIV) due to the
Doppler effect.
•A red shift means the star is moving away from Earth
•A blue shift means the star is moving towards Earth
Methods of Detecting Extrasolar
Planets
Pulsar Timing
•A pulsar is a neutron star: the small,
ultra-dense remnant of a star that has
exploded as a supernova.
•Pulsars emit radio waves extremely
regularly as they rotate. Because the
rotation of a pulsar is so regular, slight
changes in the timing of its observed
radio pulses can be used to track the
pulsar's motion.
•Like an ordinary star, a pulsar will
move in its own small orbit if it has a
planet. Calculations based on pulsetiming observations can then reveal
the geometry of that orbit
Methods of Detecting Extrasolar
Planets
Gravitational Microlensing
•The gravitational field of a star acts like a lens, magnifying the light of a
distant background star. This effect occurs only when the two stars are
almost exactly aligned.
•If the foreground lensing star has a planet, then that planet's own
gravitational field can make a detectable contribution to the lensing effect.
Methods of Detecting Extrasolar
Planets
Direct Imaging
•Planets are extremely faint light sources compared to stars and what little
light comes from them tends to be lost in the glare from their parent star.
•It is very difficult to detect them directly. In certain cases, however, current
telescopes may be capable of directly imaging planets.
http://exoplanets.org/
-The radial-velocity method and the transit
method are most sensitive to large
planets in small orbits.
-smaller planets more common than
larger & are in larger orbits
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 4.6 billion years ago (as determined by
radioactive dating).
Key Ideas
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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 (100 000 000) 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, astrometry, radial
velocity (Doppler), pulsar timing, gravitational
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.
Key Ideas

Types of Extrasolar Planets:
Hot Jupiters
 Gas Giants
 Super Earths
 Hot Neptunes
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