The Solar System - Its Origin

and Early Development

Sun and eddy

 Solar System
The Solar System consists of the Sun and the other
celestial objects gravitationally bound to it: the eight
planets, three dwarf planets and their 165 known
moons.

 4 terrestrial planets or inner planets

 The Asteroid Belt
 4 gas giants or outer planets
 The Kuiper Belt
 The Oort Cloud
 Three dwarf planets scattered thru the solar
system
General Characteristics of the Solar System
• Planetary orbits and rotation
– Planet and satellite orbits are in a common plane
– Nearly all planet and satellite orbital and spin
motions are in the same direction
– Rotation axes of nearly all planets and satellites are
roughly perpendicular to the plane of the ecliptic
 General Characteristics of the Solar System
• Chemical and physical properties of the planets
– The terrestrial planets are small, have a high density,
and are composed of rock and metallic elements
– The Jovian planets are large, have a low density, and
are composed of gases and frozen compounds
General Characteristics of the Solar System

• The three dwarf planets are Pluto, the

largest known Kuiper belt object; Ceres, the
largest object in the asteroid belt; and Eris,
which lies in the scattered disc.
 Planetary Distances: In order of
their distances from the Sun

• Mercury 0.4 AU • Light travels through

• Venus 0.7 AU space at 300,000-km/s.
• Earth 1.0 AU • So it takes about 8
• Mars 1.5 AU minutes for light from
the sun to travel 1 AU
• Jupiter 5.0 AU and reach us.
• Saturn 10.0 AU • How long would it take
• Uranus 19.0 AU light from the sun to
• Neptune 30.0 AU reach Pluto?
• Pluto (dwarf planet) 39.0 AU • 39 x 8 = 312 minutes, or
5.2 hours!
 Mass of the Solar System
• Almost all the mass in our
solar system is in the sun.

• Mass of the Solar System

• Sun 99.80%
• Jupiter 0.10%
• Comets 0.05%
• Other 7 planets 0.04%
– Total of Sun + Planets +
Comets = 99.99%
 Planets
A planet is any body in orbit around the Sun
that
a) has enough mass to form itself into a
spherical shape and
b) has cleared its immediate neighborhood of
all smaller objects.

There are eight known planets that meets

this qualification: Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune.
 Dwarf Planets
• On August 24, 2006 the
International
Astronomical Union
defined the term "planet"
for the first time,
excluding Pluto and
Images of the Asteroid Ceres As It
Rotates One Quarter

reclassifying it under the

new category of dwarf
planet along with Eris
and Ceres.
 Dwarf Planets

• A dwarf planet is not required to clear its

neighborhood of other celestial bodies. Other
objects that may become classified as dwarf
planets are Sedna, Orcus, and Quaoar.
 Small Solar System Bodies
• Natural satellites, or moons, are those
objects in orbit around planets, dwarf
planets and SSSBs, rather than the Sun
itself.
 The Solar System
• The eight bodies officially categorized as
planets are often further classified in several
ways:
• Chemical Composition
• Size
• Position Relative to the Sun
• Position Relative to the Earth
• By History
 Chemical Composition
• Terrestrial or rocky planets: Mercury, Venus,
Earth, and Mars:
• The terrestrial planets are composed primarily of
rock and metal and have relatively high densities,
slow rotation, solid surfaces, no rings and few
satellites.
• Jovian or gas planets: Jupiter, Saturn, Uranus, and
Neptune:
• The gas planets are composed primarily of
hydrogen and helium and generally have low
densities, rapid rotation, deep atmospheres, rings
and lots of satellites.
 Size
• Small planets: Mercury, Venus, Earth, Mars.
The small planets have diameters less than 13000
km.

• Giant planets: Jupiter, Saturn, Uranus and

Neptune.
The giant planets have diameters greater than 48000
km.
The giant planets are sometimes also referred to as
gas giants.
 Relative the the Sun
• Inner planets: Mercury, Venus, Earth and
Mars.
• Outer planets: Jupiter, Saturn, Uranus,
Neptune.
• The asteroid belt between Mars and Jupiter
forms the boundary between the inner solar
system and the outer solar system.
 Relative the the Earth
• Inferior planets: Mercury and Venus.
• closer to the Sun than Earth.
• The inferior planets show phases like the Moon's
when viewed from Earth.
Earth.
• superior planets: Mars thru Neptune.
• farther from the Sun than Earth.
• The superior planets always appear full or nearly
so.
 History
• Classical planets: Mercury, Venus, Mars, Jupiter, and
Saturn. Known since prehistorical times. Visible to
the unaided eye
• Modern planets: Uranus, Neptune. Discovered in
modern times. Visible only with optical aid
(telescopes)

• The IAU has recently decided that "classical" should

refer to all eight planets (Mercury thru Neptune,
including Earth but not Pluto). This is contrary to
historical usage but makes some sense from a 21st
century perspective.
Origin of the Solar System
• The Solar System is believed to have
formed according to the nebular hypothesis,
first proposed in 1755 by Immanuel Kant
and independently formulated by Pierre-
Simon Laplace.
Origin of the Solar System

• This theory holds that 4.6 billion years ago

the Solar System formed from the
gravitational collapse of a giant molecular
cloud. This initial cloud was likely several
light-years across and probably birthed
several stars.
Origin of the Solar System
• About 4.5 billion years ago it is believed that the Solar
System consisted of a large cloud of gas and dust,
called a nebula.
• This cloud started rotating, and the dust particles
combined to form planetesimals. As the cloud rotated
faster, it flattened, and the planetesimals formed.
• The Sun is at the center, and secondly, the planets in
orbit around the Sun. This model explains
qualitatively many features of the Solar System,
including the fact that the planets essentially all
revolve around the Sun in the same plane.
Nebular Hypothesis of Solar System Formation.
The Solar System – the Relative Sizes of the Planets
 The Terrestrial Planets
• Terrestrial planets seem to have experienced a
similar early history, with extensive volcanism,
cratering, and internal differentiation

• Each has a metallic core and a silicate mantle

crust, and shows evidence of continuing lava
flows and meteorite impact

• Outgassing produced an atmosphere as light

gases from the interior rose to the surface
during volcanism
 MERCURY
Mercury, the planet nearest the Sun, is the
second smallest planet in our solar system.
It is only slightly larger than the Earth's
moon. The surface is covered with craters.
This tiny planet does not have any rings or
moons.

Evidence of
craters
 MERCURY

• Diameter: one third the size of Earth

• Distance: 0.4 AU
• Atmosphere: no atmosphere
• Features: Craters with smooth plains and
most extreme temperature range
• No life because of atmosphere
• No moons or satellites
 Mercury
• Closest to the sun.
• Temperature ranges
from 427°C in
daylight to -173°C at
night.
• Revolves slowly, in
two Mercury years
three Mercury days
will have passed.
• One third the size of
the Earth.
•Period of Rotation = 88 days
•Period of Revolution = 59 days
 Mercury Missions
• Environment,
Geochemistry,
and Ranging
(MESSENGER)
is the first
mission sent to
orbit the planet
closest to the sun.
•On Oct. 6, 2008, the probe flew by Mercury for the
second time this year, using the planet’s gravity for a
critical assist needed to keep the spacecraft on track for its
orbit insertion around the planet three years from now.
 lava flows
VENUS
impact craters
Venus is one of the brightest
objects in our sky, so it is clearly
visible to the naked eye. It can
be tricky to spot because it is
always near the Sun.

It rises and sets with the Sun

each day.

Ancient civilizations believed

Venus was actually two different
objects, so they called the one
that rose the Morning Star, and
the one that set the Evening
Star.
 VENUS
•Period of Rotation = 108.2 days
•Period of Revolution = 243 days

• Almost same size as the Earth.

• Hottest surface in our solar
system. The average daytime
surface temperature is 464°C,
compared to the Earth’s 15°C.
• This is hot enough to melt lead.
• Named for the Roman goddess
of love and beauty. Originally
the Greek goddess Aphrodite.
 • Venus is covered by a thick
layer of clouds that extends
VENUS Missions between 45 and 70 km above
the surface. These rapidly-
Venus Express is ESA’s first moving clouds are mainly
composed of micron-sized
mission to Venus. Launched in droplets of sulphuric acid and
November 2005, the spacecraft other aerosols (fine solid or
arrived at the planet on 11 April liquid droplets suspended in a
gas), the origin of which is
2006 and began science unknown.
observations within a month.
Since then, it has continuously
been making new discoveries
and revising our knowledge of
Venus.
EARTH and MOON
What similarities and
differences do you notice
between the Earth and the
Moon?

Why do they have such

different surface features?
 MARS
Mars is very bright, which makes it easy to spot in the night sky. It was named after
the Roman god of war because its reddish color reminded the people of blood.

Olympus Mons
is the largest
volcano in our
solar system!

Although people have

never landed on Mars,
we have sent robotic
explorers there.

Martian crater
 Mars

• Mars is the Latin name for

Ares, the Greek god of war.
•Mars has an atmosphere that is mainly carbon dioxide.
•It is very thin, only 0.01 atmosphere’s at the surface.
•Mars even has clouds, but they are thin also.
•The winds can create dust storms that cover much of the
planet and last for months.
A surprising find made
by Mariner 9 was the
existence of several
canyons that are much
larger than Earth’s
Grand Canyon. The
largest, Valles
Marineris, is thought to
have formed by
slippage of material
along huge faults in the
crustal layer. In this
respect, it would be
comparable to the rift
valleys of Africa.
 Mars
• Mars has two very
small moons, Phobos
and Diemos.
• They are named after
the horses that pulled
Mars’s chariot.
• The larger Deimos is
only 23-km in
diameter.
•Mars is about half the size of the Earth.
•A 100 pound sixth grader would weigh 39 pounds on Mars.
•It is very cold on Mars, with the average temperature ranging
from -140° C to 20° C.
•Period of Rotation = 108.2 days Mars
•Period of Revolution = 243 days
• Mars surface has a
wide variety of
landscapes.
• Olympus Mons is the
largest volcano in our
solar system. Its base
would cover the state
of Colorado.
• It is three times taller
than Mt. Everest.
• There are many other
volcanoes on Mars, but
none seem to be active
at this time.
 Mars Missions

• There have been many missions to

Mars, starting with the Viking
craft in 1976.
• There are currently two orbiters
and two rovers collecting data on
Mars.
• Manned missions are also
currently being planned, around
2025 or so.
 Mars Missions
• Next NASA Mars Mission
Rescheduled For 2011
NASA's Mars Science
Laboratory will launch two
years later than previously
planned, in the fall of 2011.
The mission will send a
next-generation rover with
unprecedented research
tools to study the early
environmental history of The composition and markings of some
Mars. Martian rocks indicate that liquid water
was once present on Mars’s surface. The
marking shown in the center of the rock,
however, was created by a NASA rover
during chemical analysis.
 ASTEROID BELT
Most asteroids can be found in the Asteroid Belt, which is located between
Mars and Jupiter. Asteroids are rocky and metallic objects that orbit the Sun,
but are too small to be considered planets. They are known as minor planets.
Asteroids range in size from Ceres, which has a diameter of about 1000 km,
down to the size of pebbles.
The main
asteroid belt
occupies the
orbit between
Mars and
Jupiter,
between 2.3
and 3.3 AU
from the Sun.
Asteroid Belt: Ceres

• Ceres (2.77 AU) is the largest body in the

asteroid belt and its only dwarf planet. It has a
diameter of slightly under 1000 km, large enough
for its own gravity to pull it into a spherical
shape. Ceres was considered a planet when it was
discovered in the 19th century, but was
reclassified as an asteroid in the 1850s as further
observation revealed additional asteroids. It was
again reclassified in 2006 as a dwarf planet.
 Gas Giants
• Separated from the 1st
zone by the asteroid
belt, the 2nd Zone
contains the gas giants.
• Made of the lightweight
elements Hydrogen,
Helium, Carbon,
Oxygen, and Nitrogen.

•All are much larger than the Earth, with 15-300 times the mass,
and 4-11 times the diameter.
•Not believed to have solid surfaces.
•Have rings and many satellites.
 JUPITER
Jupiter, the fifth planet from the Sun, is the largest planet in our solar system.
Jupiter is so big that over 1,000 planets the size of Earth could fit into it.
It has over 60 moons and 2 rings.  Can life exist on Jupiter's moon, Europa?

The “Great Red Spot”

Is actually a huge
Storm system!

Here are a few of Jupiter’s moons

 Jupiter
• Named for Jove, the
King of the Roman
Gods.
• Roman name for the
Greek god Zeus.
• Often the term Jovian
is used to describe
things pertaining to
Jupiter. Example: the
Jovian moons.
 Jupiter
• Believed to be a failed
star, lacking the mass
to become a small star.
• Most massive planet in
solar system.
• Has over 60 satellites.
• Density is 1.33g/cm3.
• Rotates every 10 hours.
• Takes 12 years to orbit
the sun.
• Gravity almost 2.5
times that of the Earth.
 Jupiter
• The red spot is a huge
storm that has been
continuously going on
Jupiter for over 400
years.  Winds inside
this storm reach speeds
of about 270 mph. 
With a diameter of
15,400 miles, this storm
is almost twice the size
of the entire Earth.
Period of Rotation = 778.3 days
Period of Revolution = 11.86 years
 Moons of Jupiter
• The New Horizons Long Range
Reconnaissance Imager
(LORRI) captured these two
images of Jupiter's outermost
large moon, Callisto, as the
spacecraft flew past Jupiter in
late February. New Horizons'
closest approach distance to
Jupiter was 2.3 million
kilometers (1.4 million miles),
not far outside Callisto's orbit,
which has a radius of 1.9 million
kilometers (1.2 million miles).

•However, Callisto happened to be on the

opposite side of Jupiter during the spacecraft's
pass through the Jupiter system, so these
images, taken from 4.7 million kilometers (3.0
million miles) and 4.2 million kilometers (2.6
million miles) away, are the closest of Callisto
that New Horizons obtained.
 SATURN
Saturn, the sixth planet from the Sun, is the second largest planet in our solar system.
It is often called the ringed planet because many rings of dust and rocks surround it.
Saturn also has over 31 moons. Saturn with some of
its moons

Some of Saturn’s rings

Titan is a moon of Saturn that may have some

Conditions necessary for life! The picture on
the right shows an artist’s drawing of how Titan
might have looked when the Cassini-Huygen’s
probe dropped into its atmosphere in Dec., 2004.
 Saturn
• Saturn was the Roman God of
the Harvest and of Time.
• Father of Jupiter, Neptune, and
Pluto.
• The Roman name for the Greek
god Cronos.
• Saturnalia was the mid-winter
festival in Saturns honor. It
lasted seven days, and there
was much merrymaking. Public
business was suspended and
schools were closed. Parents
gave presents to their children.
• 2nd largest planet in solar
system.
Saturn
• A “day” on Saturn is a little
over 10 hours long!
• It takes 29 years to orbit the
sun.
• Almost 10 times larger than
Earth.
• Most visible rings of any
planet.
• Density is 0.69 g/cm3.
• If a large enough ocean could
be found, Saturn would float in
it!

Period of Rotation = 1,427 days

Period of Revolution = 29.46 years
 URANUS
Uranus is a very unusual planet because it sits on its side with north and south
poles sticking out the sides. It rotates around this axis, making it look like a ball
rolling around in a circle around the Sun.

some of Uranus’s moons

Black rings
 Uranus

• URANUS: Great
primeval God of
the Sky. Born of
GAIA, the Earth,
he covered the
world in the form
of a vast bronze
dome and ruled
over everything.
 Uranus
• Diameter is like 4 Earth’s.
• Mass is 14.5 Earth’s.
• Takes 84 years to revolve
around the sun.
• Day is a little over 17
hours long.
• Has more than 20 moons.
 • Uranus is considered
Uranus Axis unusual because the
planet is tipped on its
side. The poles actually
point towards the Sun.
This is due to the fact
that its magnetic field is
tilted 60 degrees from
the axis of rotation.
• It is believed that
Uranus was struck by a
large object that
knocked Uranus on its
side.
 NEPTUNE
Neptune, usually the eighth planet from the Sun, is a very cold place.
Occasionally, Pluto crosses Neptune’s orbit and becomes the eight planet.
Its bluish color comes from its atmosphere of methane gas.

Tiny Dark Moon

 Neptune
• Neptune is the Roman
god of the sea.
• The Romans modeled
him after the Greek god
Poseidon.
 Neptune
• Neptune revolves on
its axis every 18 hours.
• It takes 165 years to
revolve around the sun
once.
• Has the mass of 17
Earths.
• Has 13 moons.

•Diameter is almost 4 times larger than Earths.

•Blue-green color is from the methane in the atmosphere.
•At times it is the furthest planet from the sun.
 Neptune
• Diameter: 4 times the size of Earth
• Distance: 30 Au
• Atmosphere: 80% Hydrogen 19% Helium 1.5%
Methane
• Features: At times it is the furthest planet from the
sun. Icy clouds and enormous storms
• Life:possible life on one of its moons called Triton
 PLUTO
Pluto, usually the ninth planet from the Sun, is the smallest planet in our solar system.
Some scientists believe that Pluto once was one of Neptune’s moons, and that it
pulled out away from Neptune and made its own orbit.

Clearest view to date

Of Pluto and Charon
 Pluto
• Usually the furthest planet
from the sun.
• 2/3rds the size of our moon.
• Has one moon, Charon.
• So cold that oxygen and
nitrogen in its atmosphere is
frozen solid.
• Only planet not visited by a
spacecraft.
• Pluto takes 248 years to
make one orbit around the
sun!
 Pluto
• When Pluto comes close
enough to the sun, the
surface of solid Nitrogen
sublimates to produce a
substantial atmosphere with
winds and clouds.
• Because the planet is so
small, however, it does not
have enough gravity to bind
an atmosphere for very
long. Thus Pluto's
atmosphere is being rapidly
produced and rapidly lost at
the same time. •This means that the
atmosphere is not in
equilibrium.
• Pluto
(39 AU
Pluto
average), a
dwarf planet,
is the largest
known
object in the
Kuiper belt.

•When discovered in 1930 it was

considered to be the ninth planet; this
changed in 2006 with the adoption of
a formal definition of planet.
 New Horizons Pluto Kuiper Belt Flyby
•Pluto has a
relatively eccentric
orbit inclined 17
degrees to the
ecliptic plane and
ranging from
29.7 AU from the
Sun at perihelion
(within the orbit of
Neptune) to
49.5 AU at
The mission is expected to arrive
aphelion.
at Pluto sometime in 2015.
 COMETS
Comets are sometimes called dirty snowballs or "icy mudballs".
They are a mixture of ices (both water and frozen gases) and dust that for
some reason didn't get incorporated into planets when the solar system was formed.
This makes them very interesting as samples of the early history of the solar system.

Comets have
elliptical orbits.

When we see a comet, we

are seeing the tail of the comet
Comet Halley in 1910 as comes close to the Sun.
 Kuiper belt
• The Kuiper belt, the region's
first formation, is a great ring
of debris similar to the
asteroid belt, but composed
mainly of ice. It extends
•It is composed
between 30 and 50 AU from
the Sun. This region is mainly of small solar
thought to be the source of system bodies, but
short-period comets, such as many of the largest
Halley's Comet. Kuiper belt objects,
such as Quaoar,
Varuna, and Orcus,
may be reclassified as
dwarf planets.