Structure & Formation of the
Solar System
• What is the Solar
System?
– The Sun and
everything
gravitationally
bound to it.
The planets to scale with a portion of the
Sun visible in the background.
• There is a certain
order to the Solar
System.
• This gives us
information on its
formation.
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Part 1: Structure of the Solar System
• All the planets orbit the
Sun in the same
direction.
• All the planets orbit
within nearly the same
plane. Like a disk.
• Two type of planets
– Solid, rocky, small
planets close to the Sun
(like Earth)
– Gaseous, large planets
far from the Sun (like
Jupiter)
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The Sun
• The Sun is a star.
• It is completely gaseous.
• It emits light and heat through
nuclear fusion in its core.
• It is by far the largest object in
the Solar System. 700 times
more massive than all of the
other objects in the Solar
System put together.
• It is composed mostly of
Hydrogen and Helium gas and
traces of many other elements.
• The Sun spins on its axis
counter-clockwise.
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The Planets
In order of
increasing
distance from the
Sun:
– Mercury
– Venus
– Earth
– Mars
– Jupiter
– Saturn
– Uranus
– Neptune
– Pluto
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The Planets
• All the planets
orbit in the
same direction
counterclockwise as
seen from
above Earth’s
North Pole.
• All the planets
spin counterclockwise too
except for
Venus, Uranus
and Pluto.
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The Inner or Terrestrial Planets
• Mercury, Venus,
Earth and Mars share
certain
characteristics:
– All are rocky bodies.
– All have solid
surfaces.
– Except for Mercury
all have at least a
thin atmosphere
• They are called
Terrestrial planets
because of their
resemblance to
Earth.
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The Outer or Jovian Planets
• Jupiter, Saturn,
Uranus and Neptune
share certain
characteristics:
– All are large, gaseous
bodies.
– All have very thick
atmospheres, with
possibly liquid
interiors and solid
cores
– All have rings
• They are called
Jovian planets
because of their
resemblance to
Jupiter.
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Pluto
• Pluto is unlike any of the
terrestrial or jovian
planets.
– much farther from the Sun
than the terrestrial planets.
– much smaller than any
jovian planet.
– composition is thought to
be a mixture of ice and
rock
• It is similar to some of the
satellites of the jovian
planets and similar to
some asteroids.
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Pluto
Artist’s conception of detected
TNOs.
• After more rocky/icy
bodies were
discovered beyond
Neptune’s orbit in the
early 2000s…
• Pluto’s classification
was changed from
planet to dwarf planet
by a vote of the
International
Astronomical Union in
2006.
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Current Planet Definition
1. Must orbit the Sun
2. Must be massive enough to form a sphere
by its own gravity
3. Must have cleared its orbit
A. Pluto fails this last criterion: its mass is only
7% of the total mass of objects in its orbit;
B. Compare to Earth, which is 1.7 million times
the mass of any debris in its orbit
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Satellites (Moons)
• Most of the planets
have satellites.
• Most of the satellites
orbit in the equatorial
plane of the planet.
• Most satellites orbit
counter-clockwise.
Ganymede, Callisto, Io, and Europa.
• The jovian planets
Four of Jupiter’s largest satellites.
have more than a
These were discovered by Galileo
dozen satellites each.
Galilei and together are called the
Galilean satellites of Jupiter.
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Comets and Asteroids
• The Solar System is
filled with millions of
smaller bodies.
• Comets - composed of
ice and rock
• Asteroids - composed of
rock and/or metal
• There is also dust in
space which can be seen
in meteor showers
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Comets and Asteroids
• Most of the estimated 1
trillion comet nuclei
originate in the spherical
Oort cloud
• The remainder likely
come from the Kuiper
belt, just beyond
Neptune’s orbit
• Most asteroids lie in the
Asteroid belt, between
the orbits of Mars and
Jupiter and beyond Pluto
(in the Kuiper Belt)
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