UranusRadius: 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 hrsYear: 84 yrsDistance from sun: 19 AU (earth 1

AU) = 108 light-minutesEquatorial g = 8.9 m/s2

Moons: 27Axis of rotation: 98° (earth 23.5)

Structure

True color False ColorShowing 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

Hubble photo showing rings and moons

Voyager photo looking through the rings

Voyager photo showing ring detail

Uranian MoonsUranus (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!

Roughly half ice, half rock and heavily cratered. See the mountain?

•Tidally locked!•Second discovered, but farthest out (of major moons)•Likely the oldest of the moons (cratering)•Seasons are 42 years long!

Hamlet

Othello

Titania

1600 km long trench

Crater

•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.

NeptuneRadius: 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 hrsYear: 164 yrsDistance from sun: 30 AU (earth 1

AU) = 200 light-minutesEquatorial g = 11.2 m/s2

Moons: 27Axis of rotation: 28° (earth 23.5)

Note “the great dark spot”

Pretty Boring.

Structure

•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?IR photo of Neptune

Different colors show different temperatures

The Great 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.

Voyager photo of Dark Spot

“Cirrus” clouds in the upper atmosphere—note the shadows (Voyager 2)

Neptune Moons

•Triton is the largest satellite of Neptune. It is one of only three objects in the solar system known to have a nitrogen-dominated 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 and Triton (lower right), both crescent as Voyager flies away.

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?