PES 105        Fall 2001
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General Astronomy I
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Lecture Notes:

Uranus

text: Chapter 9: Section 9.3

Introduction and General Properties

Here is a good link for information about the Uranus: http://seds.lpl.arizona.edu/billa/tnp/uranus.html

Here is a good link for information, pictures and animations about Uranus: http://www.planetscapes.com/solar/eng/uranus.htm

Here is a link with pictures of Uranus: http://antwrp.gsfc.nasa.gov/apod/index/Uranus.html

 discovered in 1781

(doubled size of known solar system !)

Uranus is much smaller than Jupiter or Saturn

mass = 15 x Earth

volume = 64 x Earth

albedo = 0.66 . . . . cloud covered

density = 1.3 g/cm3

=> more like gas or liquid

Motions

orbit:

  • orbital period = 84 years

rotation:

  • rotation period = 17 hours
    • fast
  • equator rotates faster than poles
    • "differential rotation"
  • rotation axis tilted 98 degrees
    • laying on it's side !
    • from Earth looks like a bull's eye
    • long seasons
    • was this from a collision with a giant planetisimal ?

    rotation of Uranus

Figure 9.22 also shows this tilt. [Link to Figure 9.22]

Here is a link to a picture showing how the planet is oriented.

Interior

observe magnetic field

since it rotates, expect liquid inside

magnetic axis is tilted a lot from rotation axis - Why ?

tilt of Uranus magnetic axis

This animation shows more about the magnetic field: http://www.planetscapes.com/solar/cap/uranus/field.htm

 

Internal structure:

cross section of Uranus interior

higly differentiated

not enough pressure for liquid hydrogen or liquid metallic hydrogen

Figure 9.19 also show a cross section of Uranus. [Link to Figure 9.19]

no obvious heat source inside

Atmosphere

Composition: (from spectroscopy)

  • hydrogen
  • helium
  • methane
    • reflects blue light, absorbs red light
    • gives Uranus blue color

     

     atmosphere of Uranus

Ciculation

from:
  • weak convection
    • mainly from distant Sun
  • rotation

see faint belts and zones

fairly uniform temperature over planet (efficient circulation)

History

basically the same as other gas giants !

except a possible collision with a giant planetisimal early in the history - tilting planet on side

Moons:

15 moons

  • mainly ice and some rock
  • covered with dark dust
  • all smaller than our Moon
  • surfaces are old and cratered
  • all in synchronous orbit

    Moon and ring system of Uranus

most interesting moon: Miranda (#11)

patchwork quilt of:
  • old regions (many craters)
  • young regions
  • deep canyons and high mountains

Figure 9.21 shows pictures of features on Miranda. [Link to Figure 9.21]

Rings

  • discovered in 1977
  • 11 rings
  • each particle orbits independently (obey Kepler's 3rd law)
  • particles are dark
  • rings are narrow and thin
  • particles are large (about 1 meter in size)
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