Download Our Solar System

Our Solar System
Origins of the Solar System
Astronomy 12
Learning Outcomes (Students will…)
-Explain the theories for the origin of the solar system
-Distinguish between questions that can be answered by science and those
that cannot, and between problems that can be solved by technology and
those that cannot with regards to solar system formation.
-Estimate quantities of distances in parsec. Estimate the age of the solar
system.
-Describe and apply classification systems and nomenclature used in the
sciences. Classify planets as terrestrial vs. Jovian, inner vs. outer, etc.
Classify satellites. Classify meteoroid, asteroid, dwarf planet, planet.
Classify comets as long period vs. short period. etc
-Formulate operational definitions of major variables. Given data such as
diameter and density describe the properties that divide the planets and
moons into groups.
-Tools and methods used to observe and measure the inner and the outer
planets and the minor members of the solar system
Our Solar System
Our solar system is made
up of:
 Sun
 Eight planets
 Their moons
 Asteroids & Meteroids
 Comets
Inner Planets
The inner four rocky planets
at the center of the solar
system are:
Mercury
Venus
Earth
Mars
Mercury
Planet nearest the sun
 Second smallest planet
 Covered with craters
 Has no moons or rings
 About size of Earth’s moon

Venus
Sister planet to Earth
 Has no moons or rings
 Hot, thick atmosphere
 Brightest object in sky besides sun and
moon (looks like bright star)
 Covered with craters, volcanoes, and
mountains

Earth
Third planet from sun
 Only planet known to have life and
liquid water
 Atmosphere composed of Nitrogen
(78%), Oxygen (21%), and other gases
(1%).

Mars
Fourth planet from sun
 Appears as bright reddish color in the
night sky
 Surface features volcanoes and huge
dust storms
 Has 2 moons: Phobos and Deimos

Asteroid Belt
Separates the inner, terrestrial planets
from the outer, Jovian planets
 Contains ~100,000 asteroids.
 Largest known asteroid: 4 Vesta
 Largest object : Ceres (dwarf planet)

Outer Planets
The outer planets composed
of gas are :
Jupiter
Saturn
Uranus
Neptune
Jupiter
Largest planet in solar system
 Brightest planet in sky
 At last count, 65 moons: 5 visible from
Earth
 Strong magnetic field
 Giant red spot
 Rings have 3 parts: Halo Ring, Main
Ring, Gossamer Ring

Saturn






6th planet from sun
Beautiful set of rings
62 moons
Largest moon, Titan,
Easily visible in the night
sky
Voyager explored Saturn
and its rings.
Uranus





7th planet from sun
Has a faint ring system
27 known moons
Covered with clouds
Uranus sits on its side with the north
and south poles sticking out the
sides.
Neptune
8th planet from sun
 Discovered through math
 12 known moons
 Triton largest moon
 Great Dark Spot thought to be a
hole, similar to the hole in the
ozone layer on Earth

A Dwarf Planet

Pluto is a small solid icy
planet is smaller than the
Earth's Moon.
Pluto



Never visited by
spacecraft
Orbits very slowly
Charon, its moon, is
very close to Pluto
and about the same
size
Two Types of Planets: Terrestrial and Jovian
Why?
Asteroids
Small bodies
 Believed to be left over
from the beginning of
the solar system
billions of years ago
 100,000 asteroids lie in
belt between Mars and
Jupiter
 Largest asteroids have
been given names

Comets
Small icy bodies
 Travel past the Sun
 Give off gas and dust as
they pass by

Anatomy of a Comet
Anatomy of a Comet
Anatomy of a Comet
How was the Solar System
Formed?
A viable theory for the formation of the solar
system must be:
• based on physical principles (angular
momentum, the law of gravity, the law of
motions)
• able to explain all (at least most) the
observable facts with reasonable
accuracy
• able to explain other planetary systems
How was the Solar System
Formed?
A viable theory for the formation of the solar system
must account for 4 characteristics:
1.
2.
3.
4.
Patterns of motion
Two types of planets
Asteroids & comets
Exceptions to patterns
Patterns of Motion
•
•
•
All the planets orbit the Sun in the same direction
The rotation axis of most of the planets and the Sun are
roughly aligned with the rotation axis of their orbits.
Orientation of Venus, Uranus, and Pluto’s spin axes are
not similar to that of the Sun and other planets.
Why do they spin in
roughly the same
orientation?
Why are they
different?
What does the solar system look like
from far away?
•
Sun, a star, at the center
•
Inner (rocky) Planets
(Mercury, Venus, Earth,
Mars) ~ 1 AU
•
Asteroid Belt ~ 3 AU
•
Outer (gaseous) Planets
(Jupiter, Saturn, Neptune,
Uranus) ~ 5-40 AU
•
Kuiper Belt ~ 30 to 50 AU
-includes Pluto
•
Oort Cloud ~ 50,000 AU
Bode’s Law
•A rough rule that predicts the spacing of the planets in the Solar System
•To find the mean distances of the planets, beginning with the following simple sequence of
numbers:
0 3 6 12 24 48 96 192 384
•With the exception of the first two, the others are simple twice the value of the preceding
number.
•Add 4 to each number:
4 7 10 16 28 52 100 196 388
•Then divide by 10:
0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 38.8
Planet
Actual Distance (AU)
Bode’s Law
Mercury
0.39
0.4
Venus
0.72
0.7
Earth
1.00
1.0
Mars
1.52
1.6
Jupiter
5.20
5.2
Saturn
9.54
10.0
Uranus
19.2
19.6
Neptune
30.1
38.8
Works
for
moons
too!
Where are the asteroids?
Most asteroids are
located in two regions:
•Asteroid belt
•Orbit of Jupiter… the
Hildas (the orange
"triangle" just inside the
orbit of Jupiter) and the
Jovian Trojans (green).
The group that leads
Jupiter are called the
"Greeks" and the trailing
group are called the
"Trojans"
Where are the comets?
Kuiper Belt
A large body of small
objects orbiting (the short
period comets <200 years)
the Sun in a radial zone
extending outward from the
orbit of Neptune (30 AU) to
about 100 AU. Pluto maybe
the biggest of the Kuiper
Belt object.
Oort Cloud
Long Period Comets
(period > 200 years) seems
to come mostly from a
spherical region at about
50,000 AU from the Sun.
Exceptions to Patterns
•Uranus has different axial tilt
•Some moons larger than others
•Some moon have unusual orbits
Planetary Nebula or Close
Encounter?
Historically, two hypothesis were put forward to explain the formation of the solar
system….

#1 - Gravitational Collapse of Planetary Nebula
Solar system formed form gravitational collapse of an interstellar cloud of gas

#2 - Close Encounter (of the Sun with another star)
Planets are formed from debris pulled out of the Sun during a close encounter
with another star. But, it cannot account for


The angular momentum distribution in the solar system,
Probability for such encounter is small in our neighborhood…
Astronomers favour Hypothesis #1
The Nebular Theory* of Solar System
Formation
Interstellar Cloud (Nebula)
*It
is also called the
‘Protoplanet Theory’.
Gravitational Collapse
Protosun
Heating  Fission/Fusion
Sun
Leftover Materials
Asteroids
Protoplanetary Disk
Condensation (gas to solid)
Metal, Rocks
Gases, Ice
Accretion
Nebular
Capture
Terrestrial
Planets
Jovian
Planets
(depends on temperature)
Leftover Materials
Comets
Collapse of the Solar Nebula
Gravitational
Collapse
Denser region in a interstellar cloud, maybe compressed
by shock waves from an exploding supernova, triggers
the gravitational collapse.
1.
2.
3.
Heating  Protosun  Sun
In-falling materials loses gravitational potential energy, which were converted into kinetic
energy. 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.
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.
Flattening  Protoplanetary disk.
The solar nebular flattened into a flat disk. Collision between clumps of material turns the
random, chaotic motion into a orderly rotating disk.
This process explains the orderly motion of
most of the solar system objects!
The Solar
Nebula
Hypothesis
Basis of modern theory
of planet formation.
Planets form at the
same time from the
same cloud as the star.
Planet formation sites
observed today as dust
disks of T Tauri stars.
Sun and our solar system
formed ~ 5 billion years ago.
Beta Pectoris dust disk
Planetesimals forming planets
Evidence
for Ongoing
Planet
Formation
Many young
stars in the Orion
Nebula are
surrounded by
dust disks:
Probably sites of
planet formation
right now!
Dust Disks
around
Forming
Stars
Dust disks around
some T Tauri stars
can be imaged
directly (HST).
The Story of Planet Building
Planets formed from the same protostellar material
as the sun, still found in the sun’s atmosphere.
Rocky planet material formed from clumping
together of dust grains in the protostellar cloud.
Mass of less than ~ 15
Earth masses:
Planets can not grow by
gravitational collapse
Earthlike planets
Mass of more than ~ 15
Earth masses:
Planets can grow by
gravitationally attracting material
from the protostellar cloud
Jovian planets (gas giants)
Extrasolar Planets
An extrasolar planet,
or exoplanet, is a
planet beyond our solar
system, orbiting a star
other than our Sun
Information obtained primarily from wikipedia.org
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
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.