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The Jovian Planets, Part III
Uranus and Neptune
URANUS
The God of the Heavens
Physical Data
Discovered by William Herschel in 1781
 Diameter: 51,118 km (4.01 Dearth)
 Mass: 8.69x1025 kg (14.54 Mearth)
 Density: 1.24 g/cm3
 Rotation Period: 17.24 hours
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 Tilt of Axis: 98 (retrograde rotation!)
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 Surface Temperature: 52 K (-366 F)
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Physical Data
Orbital Semi-Major Axis: 19.18 AU
 Orbital Period: 84.01 years
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 Orbital Inclination: 0.8
 Orbital Eccentricity: 0.047
 Surface Gravity: 0.919 Earth gravity
 Satellites: 27 as of 2011
 Magnetic Field: yes
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Uranus’ Interior
MOLECULAR HYDROGEN
ATMOSPHERE
ICE
ROCK
The Discovery of Uranus
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First discovered planet
even though at its
closest to earth it can
be seen with the naked
eye
Was recorded 22 times
as a star on star charts
before W. Herschel
discovered it as a
planet in 1781
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Uranus’ Motions
N
S
N
SUN
N
S
S
N
S
Uranus rotates on its side, producing strange
seasons and day-night patterns

Uranus’ Atmosphere
COMPOSITION:
 85% Hydrogen
 15% Helium
 Traces of Methane
CLOUDS:
 Mostly made of methane ice
 Featureless cloudtops (inconspicous bands)
Uranus’ Magnetic Field
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Magnetic dipole is
offset 31% from the
center of the planet
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Tilted -59 from
rotational axis
Comparable in
strength to Earth’s
(0.74 Earth’s)
Uranus has aurora and
radio emissions
Uranus’ Rings
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Found from star
occultations in 1977
Thought to be made
of stone
Uranus also has
partial rings called
“ring arcs”
Also has sheperd
satellites
Uranus’ Moons
All are named after William Shakespeare
and Alexander Pope characters
 There are 15 known moons

Uranus’ Moons
MIRANDA:
 Surface is a weird mix
of old and new terrain
 It has been proposed
than it was shattered
and reassembled in
this way
 There was not enough
heat to fuse it
smoothly together
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Uranus’ Moons
ARIEL:
 Youngest surface of
the Uranian Satellites
 There is evidence of
tectonic activity
 It has faults over 10
km deep
Uranus’ Moons
TITANIA:
 Largest of Uranus’
moons
 Has faults up to 100
km across
 Has a heavily cratered
surface
NEPTUNE
GOD OF THE SEA
Physical Data
First observed in 1846 by Johann Galle
 Diameter: 49,500 km (3.89 Dearth)
 Mass: 1.030x1026 kg (17.23 Mearth)
 Density: 1.61 g/cm3
 Rotation Period: 16.11 hours
o
 Tilt of Axis: 28.76
o
 Surface Temperature: 57 K (-357 F)

Physical Data
Orbital Semi-Major Axis: 30.06 AU
 Orbital Period: 164.79 years
o
 Orbital Inclination: 1.8
 Orbital Eccentricity: 0.009
 Surface Gravity: 1.19 Earth’s gravity
 Satellites: 13 as of 2011
 Magnetic Field: yes

The Discovery of Neptune
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It’s existence was calculated before it was
observed from variations of Uranus’ orbit from
what was predicted
Calculations were made by U.J. Leverrier, sent to
Johann Galle at Berlin Observatory, and he found
Neptune after searching for 30 minutes
Galileo actually recorded Neptune twice in 1612
and 1613 in his notebooks as a background star in
his drawings of Jupiter
Neptune’s Interior
ATMOSPHERE
MOLECULAR HYDROGEN
ICE
ROCK
Similar to Uranus
Neptune’s Atmosphere
75% Hydrogen
 25% Helium
 Small amounts of: Methane, Ammonia &
Acetylene
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There are three majors cloud-top features:
The Great Dark Spot
Dark Spot 2
Scooter
Neptune’s Atmosphere
The Great Dark Spot:
 Anti-cyclone with a
circulation period of
16 days
 About the size of
Earth
 In southern
hemisphere
Neptune’s Atmosphere
Great Dark Spot
Scooter
Dark Spot 2
Dark Spot 2:
 Smaller cyclone in S.
hemispere
Scooter:
 Fast rotating
 Rapidly changes shape
Neptune’s Magnetic Field
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Magnetic dipole is
offset 55% from
center of Neptune
o
Tilted -47 with
respect to rotational
axis
Has a field strength of
0.4x Earth’s at the
equator
Has aurora and radio
emissions
Neptune’s Rings
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Discovered in 1981
Brighter areas are ring
arcs
There is a total of 5
rings, all very thin
Neptune’s Moons
TRITON:
 Has thin atmosphere,
geysers, and strange
“cantaloupe terrain”
 Diameter: 3000km
Neptune’s Moons
Proteus:
 Second largest moon
of Neptune discovered
by Voyager
 Surprisingly, Neried,
Neptune’s third largest
moon was discovered
from the ground
before Proteus