Download The Outer Solar System

25.4
 Uranus was discovered
in 1781, but its rings
were not found until
1977. Like Uranus
itself, the rings were
discovered by
accident. This falsecolor infrared image
was taken by the
Hubble Space
Telescope.
Gas Giants
 The four gas giants are thought to have small, dense
cores and thick atmospheres that are mostly hydrogen
and helium.
Gas Giants
Jupiter, Saturn, Uranus, and Neptune are very different
from the terrestrial planets.
• They are much colder because of their distance from the sun.
• All four planets are much larger and more massive than the
terrestrial planets.
• They are often referred to as the gas giants because they are
composed mainly of hydrogen and helium.
Gas Giants
None of the gas giants have
solid surfaces.
If you tried to land a spaceship
on one, you would sink into the
planet until the intense pressure
of the atmosphere crushed the
ship.
 The pressure is so great inside
each planet that hydrogen and
helium exist mostly in liquid
form.
Gas Giants
 Gas giants have many moons, most of which revolve in
the same direction that the planets rotate.
 Each of the gas giants is surrounded by rings. A ring is
a disk made of many small particles of rock and ice in
orbit around a planet.
 Rings are so close to the planet that gravitational forces
are very large
Prevented the ring particles from clumping together to
form moons.
Gas Giants
 The outer planets consist of the four gas giants. Pluto,
formerly considered a planet, was reclassified as a
dwarf planet in 2006.
Jupiter
 Jupiter is the largest and most massive planet in our
solar system.
Jupiter
Jupiter’s Atmosphere
Jupiter’s clouds move rapidly because Jupiter itself
rotates rapidly
one day on Jupiter is less than 10 Earth hours.
The brown cloud bands are colder and move faster
around the planet than the white bands.
Jupiter
 Sometimes storms occur at the
boundaries between these brown and
white bands.
The Great Red Spot is a huge storm that
rotates around its own center like a
hurricane. It is caught between two
bands of winds blowing in opposite
directions.
 The Great Red Spot was first observed in
1664 but may be much older.
Jupiter
 The Great Red
Spot, is a giant
storm much larger
than Earth.
Jupiter
Jupiter’s Moons
Jupiter has at least 63 moons.
• Most of them are small, less than 200 kilometers in
diameter.
• Ganymede and Callisto are similar in size to Mercury.
• Io is covered with actively erupting volcanoes.
• Io and Europa are somewhat smaller, about the size of
our moon.
Jupiter
 Ganymede, Io, and Europa have
metal cores and rocky mantles.
 Io is covered with actively
erupting volcanoes.
 Ganymede, Europa, and Callisto
are covered with ice.
 On Europa, the icy crust appears
to rest on top of a liquid saltwater
ocean. Scientists hypothesize
that Europa is the most likely
place in the solar system, other
than Earth, to support life.
Jupiter
Io is the most volcanically
active body in the solar
system. Io’s volcanic
eruptions consist mainly of
liquid sulfur.
Europa may have a liquid
water ocean beneath its icy
surface. The dark lines are
wide fractures in Europa’s
crust.
Saturn
 Saturn’s rings are the largest and most visible from
Earth.
Saturn
Saturn, the second largest planet in the solar system, is
best known for its rings.
• The rings are made of particles of ice and ice-coated rock.
• These particles are generally between a few micrometers and
10 meters across, with most particles being snowball-sized.
• The rings are about 274,000 kilometers in diameter, yet are
only tens of meters thick.
Saturn
Saturn’s Atmosphere
Like Jupiter, Saturn has colorful
banding in its atmosphere.
Saturn’s atmosphere is the largest of
any planet in the solar system. Saturn
also has the lowest average density,
less than the density of liquid water.
Saturn’s atmosphere is made mostly of
hydrogen and helium, with small
amounts of other elements
Saturn
Saturn’s Moons
Astronomers have found at least 56 moons orbiting
Saturn.
• Most of these moons are very small.
• Titan is larger than Mercury. Titan is the only planetary
moon with a thick atmosphere.
Uranus
 The axis of Uranus’ rotation is tilted more than 90°.
Uranus
Because Uranus is so far from the sun, it is very cold.
Uranus’ atmosphere is mostly hydrogen and helium.
Large amount of methane, which gives the planet a
distinct blue-green appearance.
Uranus
Structure of Uranus
Like Jupiter and Saturn, Uranus has a dense core.
This core is thought to be surrounded by a thick mantle
layer of liquid water and dissolved ammonia.
A layer of liquid hydrogen and helium surrounds the
mantle.
Uranus
Uranus has rings, although they are not as visible as
Saturn’s.
Uranus has at least 27 moons, though most are quite
small.
Uranus
A Tilted Planet
The most unusual characteristic of Uranus is that it
lies nearly on its side.
• Uranus rotates in a direction opposite to the direction of
its revolution around the sun. Uranus’ rings and moons
revolve about the same tilted axis.
Uranus
 Uranus’ northern and southern hemispheres alternate
being exposed to the sun for many years, which causes
immense storms.
 No one knows for sure why Uranus’ axis is so tilted.
 Scientists hypothesize that the tilt may have been
caused by a collision with another large planetary body
early in its history.
Neptune
 Neptune’s bluish color comes from the methane in its
atmosphere.
Neptune
Neptune is so far from the sun that it takes a very long
time—165 Earth years—for it to make one revolution.
Neptune has about the same composition and is about
the same size as Uranus.
Neptune
Neptune has clearly visible cloud patterns in
its atmosphere.
• Thin, wispy clouds form high within Neptune’s
atmosphere.
• Neptune’s clouds are made of methane ice
crystals.
Neptune also has large storms in its
atmosphere.
One storm, observed by the Voyager 2 space
probe in 1989, was called the Great Dark
Spot, but by 1994, the storm was gone.
Neptune
 The Great Dark
Spot, visible near the
center, was similar in
size to Earth.
Neptune
Neptune has thin rings very similar to the rings of
Uranus.
In addition, Neptune has at least 13 moons. Triton, the
only large moon, has a thin atmosphere and an icy
surface.
Dwarf Planets
 A dwarf planet, like a planet, is spherical and orbits the
sun directly. But unlike a planet, a dwarf planet has
not cleared the neighborhood around its orbit.
 Pluto, which for many years had been considered the
ninth and most distant planet in the solar system, was
reclassified as a dwarf planet.
Dwarf Planets
A dwarf planet is too small for its
gravity to attract all the nearby
debris, so dwarf planets tend to
orbit in zones that contain many
other objects.
Pluto is much smaller than the
inner or outer planets. Its diameter
is about half that of Mercury.
The density of Pluto is similar to
that of Triton, suggesting a mixture
of ice and rock.
Dwarf Planets
Pluto’s orbit around the sun is more
elliptical than those of the planets. Pluto
actually swings closer to the sun at times
than Neptune.
Like Uranus, Pluto has a rotation axis
that is tilted more than 90°.
Pluto also has three moons, Charon, Nix,
and Hydra.
Dwarf Planets
 The New Horizons space probe will reach the dwarf
planet Pluto and its three moons in the year 2015.
Dwarf Planets
 Other known dwarf planets include Eris and the
asteroid Ceres.
Comets and Meteoroids
 Comets are dusty pieces of ice and rock that partially
vaporize when they pass near the sun.
 Meteoroids are pieces of rock, usually less than a few
hundred meters in size, that travel through the solar
system.
Comets and Meteoroids
Certain ancient meteoroids have been largely
unaltered since the birth of the solar system.
• These meteoroids are the oldest remnants of the early
solar system.
• Scientists have used radioactive dating to determine
their absolute age and have found that the solar system
is about 4.6 billion years old.
The Edge of the Solar System
 Most of the objects in the Kuiper belt lie in a
doughnut-shaped region close to the ecliptic.
 Beyond the Kuiper belt lies a great reservoir of comets
called the Oort cloud.
The Edge of the Solar System
Astronomers estimate that
thousands of solar system objects
exist beyond Neptune’s orbit.
• These objects are found largely in two
regions, the Kuiper belt and the Oort
cloud.
• The Kuiper belt extends from
Neptune’s orbit out to about 100 AU
or more from the sun.
• Pluto is an example of a Kuiper belt
object.
The Edge of the Solar System
The solar system extends much
farther out than the Kuiper belt.
The Oort Cloud is a very sparse
sphere of comets thought to
encircle the solar system out to a
distance of about 50,000 AU.
Occasionally objects from the
Oort cloud enter the inner solar
system, where they appear as
comets.
The Edge of the Solar System
 Located in the outer
reaches of the solar
system, the Oort cloud
is a sphere of comets
surrounding the sun
and planets.