Universe 8e Lecture Chapter 8 Origin of Our Solar System

1
The Origin of Our Solar System II
2
(No Transcript)
3
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?

4
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?

5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
The Solar Nebular Theory
Interstellar Cloud (Nebula)
(depends on temperature)
15
Major Physical Processes in Solar Nebular Theory

• 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.

16
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.

17
(No Transcript)
18
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.

19
Major Physical Processes in Solar Nebular Theory

• Heating
• Spinning
• Flattening
• This process explains the orderly motion
• of most of the solar system objects!

20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
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

33
Disk Instability Model for Jovian Planet Formation

• Gases rapidly accrete and condense to form Jovian
  planets without a solid core

34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
Extrasolar Planets
An extrasolar planet, or exoplanet, is a planet
beyond our solar system, orbiting a star other
than our Sun
41
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
42
Types of Extrasolar Planets
Pulsar Planet A type of extrasolar planet that
is found orbiting pulsars, or rapidly rotating
neutron stars Example PSR B125712 in the
constellation Virgo
43
Types of Extrasolar Planets
Gas Giant A type of extrasolar planet with
similar mass to Jupiter and composed on
gases Example 79 Ceti b
44
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
45
OGLE-2005-BLG-390Lb
46
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
47

• Gliese 581 b

48
(No Transcript)
49
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.

50
(No Transcript)
51
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.

52
(No Transcript)
53
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

54
(No Transcript)
55
(No Transcript)
56
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 pulse-timing observations can then
  reveal the geometry of that orbit

57
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.

58
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.

59
http//exoplanets.org/
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64
(No Transcript)
65
(No Transcript)
66
(No Transcript)
67
-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
68
Key Ideas

• 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).

69
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.

70
Key Ideas

• 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.

71
Key Ideas

• 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 protosuns
  center became high enough to ignite nuclear
  reactions that convert hydrogen into helium, thus
  forming a true star.

72
Key Ideas

• 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.

73
Key Ideas

• Types of Extrasolar Planets
• Hot Jupiters
• Gas Giants
• Super Earths
• Hot Neptunes