Uranus
Radius: 25,600 km (4 x earth)
Mass: 8.7e25 kg (15 x earth)
Density: 1.27 kg/m3 (earth 5.5
kg/m3)
Day: 17.24 hrs
Year: 84 yrs
Distance from sun: 19 AU (earth 1
AU) = 108 light-minutes
Equatorial g = 8.9 m/s2
Moons: 27
Axis of rotation: 98° (earth 23.5)
Structure
True color
False Color
Showing cloud structure
(mostly the result of
temperature differences)
•Uranus’ atmosphere is almost solely CH4 with a haze of other icy hydrocarbons at the top.
These cloud particles are regularly created and destroyed, recycling the atmosphere.
•Uranus has wind bands like Jupiter and Saturn.
Uranian rings
Voyager photo looking through the
rings
Hubble photo showing rings and
moons
Voyager photo showing ring detail
Uranian Moons
Uranus (not to scale) with
(counterclockwise from front) Titania
(largest), Miranda, Ariel, Oberon, and
Umbriel. Miranda is thought to have
been destroyed and reassembled by
gravity.
An IR image taken by the Subaru
telescope of Miranda and Ariel in
orbit.
Uranus’ rings can also be seen.
Miranda (Voyager 2)
• South pole
• 480 km across
• distinctly sectioned (broken and
reassembled)
•Much more inclined orbit (not the
original orbit)
•Earlier closer in 3:1
resonance with Umbriel
•Resonance FAIL, Miranda
moves on
This way to Uranus!
Othello
•Tidally locked!
•Second discovered, but
farthest out (of major
moons)
•Likely the oldest of the
moons (cratering)
•Seasons are 42 years
long!
Hamlet
Roughly half ice, half rock and heavily cratered. See the mountain?
Titania
Crater
1600 km long trench
•Tidally Locked (like Luna)
•Lots of water ice
Taken from 1,000,000 km
behind Uranus on Voyager
2’s way to Neptune.
(1 px = 30 mi)
The white edge is
hydrocarbon haze in the
upper atmosphere.
Neptune
Radius: 24,800 km (4 x earth)
Mass: 1.0e26 kg (17 x earth)
Density: 1.64 kg/m3 (earth 5.5
kg/m3)
Day: 16 hrs
Year: 164 yrs
Distance from sun: 30 AU (earth 1
AU) = 200 light-minutes
Equatorial g = 11.2 m/s2
Moons: 27
Axis of rotation: 28° (earth 23.5)
Note “the great dark spot”
Pretty Boring.
Structure
IR photo of Neptune
Different colors show different
temperatures
•Clouds are H, He, CH4
•Dark spot is(was) surrounded by
frozen CH4
•Cloud bands rotate like other gas
giants
•700 mph winds at equator! (not
as fast as Saturn, but still pretty
powerful) Otherwise similar to
Uranus
•Perhaps a big diamond core?
The Great Dark Spot
Voyager photo of Dark Spot
•First observed in 1989
•surrounded by frozen CH4
•1500 mph winds
•Disappeared by 1994, when
Hubble looked at it
•Replaced by another storm in the
northern hemisphere
•Storms should not happen as
such because of the lack of solar
heating in the upper atmosphere.
There must be an internal heat
source.
“Cirrus” clouds in the upper atmosphere—note the shadows (Voyager 2)
Neptune Moons
Neptune and
Triton (lower
right), both
crescent as
Voyager flies
away.
•Triton is the largest satellite of
Neptune. It is one of only three
objects in the solar system
known to have a nitrogendominated atmosphere (the
others are Earth and Saturn's
giant moon, Titan). The greenish
areas include what is called the
"cantaloupe terrain," whose
origin is unknown, and a set of
"cryovolcanic" landscapes
apparently produced by
cryogenic liquids (now frozen)
which erupted from Triton's
interior.
•Triton is the only moon that
revolves backwards around its
parent
Neptune Rings
A backlit view of Neptune’s rings. The bright spot in the middle is overexposure of the photo by
the sun.
This picture is a 591-second exposure. The long time was necessary to gather enough scattered
light from the rings to show them.
The planet is in the center, blocked out. The white dots are stars in the field behind the planet.
Can’t Commit? Try Ring Arcs!
•
•
Ring arcs are loose bunches
of ring stuff, but not enough to
smooth out. They are just
clumps that follow a ring
pattern.
The ring arcs are named
Fraternité, Égalité 1 and
Égalité 2, Liberté, and
Courage
Bye-bye, Neptune! (and
Triton)
Voyager 2
Where am I now?