Astronomy Ch. 15 Uranus

Uranus was discovered by

William Hershell in 1781

• Was looking for binary stars but noticed a green dot slightly changed positions

• There were 17 previous observations of that green dot but was always categorized as a star

• This led to the discovery of Uranus

Uranus is named after

The Greek mythology god Uranus (father of saturn and grandfather of Jupiter)

How long is one day on Uranus

17 hours

Uranus Interior

• Average internal temperature: -216 Celsius, coldest in the solar system

• Slightly denser than ice

• Has larger portion of rock and ice than Jupiter and Saturn

• Mantle slushy water, methane, and ammonia, mixed with hydrogen and silicates

• Heavy element core

Which mission is the first and only to ever visit Uranus?

Voyager 2

Uranus Magnetic field

• 0.75% of Earth’s magnetic field

• It’s magnetic field axis forms an angle of 59 degrees with the rotation axis

• Magnetic field is produced by the rotation of other parts of Uranus, not the center

Auroras on Uranus

• Detected in the ultraviolet by Voyager 2 in 1986

• 59 degrees inclined and offset from Uranus rotation axis

• Auroras not in geographic poles, but on magnetic poles

What makes the blue color on Uranus?

CH4, in H-rich atmosphere, clouds of methane ice crystals

Methane absorbs long wavelengths

The atmosphere of uranus is much more __ than that of Jupiter and Saturn

colder

Uranus is mostly formed from

Hydrogen and Methane

Cloud layer on uranus is formed from

Methane ice crystals deep in the hydrogen atmosphere

Storms in uranus atmosphere are

seasonal

Each season on uranus last

21 years

Uranus Moons

• 5 largest moons visible from earth

• They are all tidally locked to Uranus

• Total of 27 moons

• 10 of these were discovered by Voyager in 2018

• 13 near the rings

• 9 are large irregular orbits

• Most of the moons are named after shakespeares novel characters

Uranus Moons pt. 2

• Dark surfaces

• 5 large moon densities suggest that they contain relatively large rocky cores with mantles of dirty ice

• Moons orbit vertically around the planet

Uranus 5 Main Moons

1. Titania

2. Oberon

3. Umbriel

4. Ariel

5. Miranda

Titania

• Uranus’ largest moon

• heavily cratered, very active in the past

Oberon

• Uranus’ outermost moon

• Active in past

• 60 km smaller than Titania

Umbriel

• Uranus’ darkest moon

• No signs of active past

Ariel

• Uranus’ brightest moon with relatively smooth surface

• Geological activity

Miranda

• Smallest and most mysterious moon

• Innermost moon

• Surface shows signs of extreme activity

• Marked by great oval pattern of grooves called ovoids

Uranus rings were discovered

During an occultation when Uranus crossed in front of a star

How many rings does uranus have

13

Uranus Rings

• Consist of a thin layer of very dark bug boulders (no dust)

• Confined by small moons, shepherd

• Rings cannot survive for long periods and are not primordial

• Material in rings must be replenished constantly

History of Uranus

• Uranus and neptune formed closer to the sun

• Gravitational interactions then moved them out

• Highly inclined axis may have been caused by planetismal impact or by tidal interactions with Saturn

• Debris from impacts on moons could be source of rings’ particles