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The Outer Planets
Jupiter (5.20 au)
Enormous size and mass make Jupiter
undisputed giant of the solar system.
• Galileo in 1995 orbited Jupiter and
shot a probe into the atmosphere, radioed
back data for an hour before it was crushed.
• “Jovian” = giant Over 11X diameter and over 317X the
mass of Earth, Jupiter is twice as massive as all the other
planets combined!
• Colorful Clouds and a Whirlpool of Wind
– Light colored zones and dark colored bands created by jets of
wind circulating in alternating directions.
– 400 mph winds generated by convection currents, as Jupiter is
still cooling from its formation.
Jupiter’s Great Red Spot
• Giant cloud, collosal
eddy, observed for over
300 years, 25,000 miles
long and 8,700 miles
wide.
• Similar high pressure
swirls appear elsewhere
on Jupiter, Saturn, and
Neptune.
• No one knows what
sustains these systems.
What do you think?
Saturn (9.54 au)
Spectacular ring system sets
this second largest planet apart.
• 2nd largest planet and 2nd largest mass.
• 96% H, 3% He, less dense than water.
• Rocky core is embedded in an outer core of water,
methane, and ammonia.
• Above the core is liquid hydrogen 21,000 km deep
• Rocks, dust, and ice orbiting the planet form several large
rings and thousands of narrow ringlets about 10 km thick
• Has at least 30 known satellites. Its largest moon, Titan, is
unique among moons for it has its own atmosphere.
• Voyager 2 flyby in 1981 gave us close-up of rings and
1990 Hubble Telescope recorded enormous storms.
Saturn’s Rings
• Still not sure why Saturn or
any planet has rings.
• Maybe rings are the remains
of a moon smashed by an
asteroid.
• More likely, the rings are
made of particles that were
unable to concentrate into a
moon, because of the
gravitational influence of
the planet.
Uranus
(19.18 au)
A puzzling blue-green world
four times the size of Earth and
1.8 billion miles away.
• Most of our knowledge of Uranus
is from Voyager 2 which sped by in 1986.
• A planet on its side: Since its rotation is nearly parallel
with orbit about the sun, each pole spends 42 years in
darkness and 42 years in light.
• Beneath the Blue-Green Clouds:
– A small rocky core is surrounded by thick layer of ice and rock
and an outer layer of H and He.
– Methane and ammonia condense into clouds at high altitudes.
Methane gives Uranus its blue-green color.
A narrow ring system of orbiting rock and ice was
detetected by astronomers in 1977 and confirmed
by Voyager 2 in 1986.
Neptune (30.06 au)
Smallest and most distant of
the gas giants, 30,800 miles away.
• Voyager 2 reached the 8th planet on
Aug 25, 1989 revealing a blue disk with
dark bands and white clouds.
• Early in the 19C, unexplained perturbations were
observed for Uranus. This led to the eventual finding of
Neptune by astronomers in Germany and England.
• Like Jupiter and Saturn, it emits twice as much heat as it
receives from Sun.
• Atmosphere mainly H and He; like Uranus, Neptune’s
bluish color caused by clouds of methane.
Neptune: Dim rings, violent storms,
and an intriguing moon
• 4 known rings, faintly
detected; little known
• Oval shaped high-pressure
region 6,000 mi long with
supersonic winds detected by
Voyager 2.
• Of 8 satellites, Triton is
largest, a bit larger than Pluto;
has numerous impact craters,
curious pits, and volcanoes
that release nitrogen, not lava.
Pluto (39.44 au)
Pluto is a tiny, cold rocky world
with a tilted & very eccentric orbit.
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248 years per revolution about sun
2.8 billion mi away at closest approach
Only planet not visited by spacecraft
Smallest planet, (< 1,430 mi diameter) smaller than Moon
Rock-Ice composition similar to Triton
Pluto has close relationship to its single moon, Charon;
the two bodies spiral around a shared center of gravity.
• Both may be captured objects that wandered in from the
Kuiper Belt.
• Amateur astronomer Clyde Tombaugh discovered Pluto
in 1929.
Courtesy Lowell Observatory
The discovery photos for Pluto reveal the shift of one point of
light between January 23, 1930 (left), and January 29, 1930
(right). The white arrows point to Pluto.
Bodes Law, a fun math puzzle
0
+4
.4
3
6
12
24
48
96
.7
1.0 1.6
2.8
5.2
10.0
192
19.6
Bodes Law, a fun math puzzle
0
3
6
+4
.4 .7 1.0
Me V E
12
24
1.6 2.8
Ma Ast
48
96
192
5.2
Jup
10.0 19.6
Sat Uranus
Distance of each planet from the sun in Astronomical
Units (AU)
1 AU = 93 million miles, the ave distance to the Sun
Comets
“Dirty snowball” of water, ice
and dust orbits the sun
• Comets feature a head (coma)
at front, and a tail that faces away from the sun.
• Tail forms when ice is heated from sun, melts,
and spreads out as a dust-filled gas.
• Particles in tail may cause a meteor shower on
Earth if we pass through the tail.
• Famous comets include Hale-Bopp, Halley,
Hyakutake, and Shoemaker-Levy 9.