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Uranus
Neptune
And their moons
Uranus Statistics
Radius: 3.98 times Earth’s (25,559 km)
Mass: 14.54 times Earth’s (8.68 x 10^25 kg )
Density: 1.32 g/cm³ ( 23 % of Earth’s)
Surface Gravity: 8.69 m/s² (88.6 % Earth’s)
Orbit and Rotation
Radius (average.): 19 AU (2,749,000,000 km )
Year: 84 Earth Years
Sidereal Day: 17.24 Hours
Axial Tilt: 97.86º (Earth’s: 23.45°)
Neptune’s Statistics
Radius: 3.81 times Earth’s (24,764 km )
Mass: 17.13 times Earth’s (1.02 x 10^26 kg )
Density: 1.64 g/cm³ ( 30 % of Earth’s)
Surface Gravity: 11.15 m/s² ( 114% Earth’s)
Orbit and Rotation
Radius (average.): 30.06 AU
(4,496,000,000 km )
Year: 164.8 Earth Years
Sidereal Day: 16.11 hours
Axial Tilt: 29.56º (Earth’s: 23.45°)
Uranus and Neptune
True Twins
They are gas giants like Jupiter made
mostly of Hydrogen and its
compounds, chiefly H2O.
About the same size color and
structure, Uranus and Neptune are
true twins.
But both have large amounts of
methane in their atmosphere that
absorb red making them appear blue
Their interiors have a large layer of
compressed water around their
cores.
Effects of Uranus’ Tilt
For a person at a Pole the “daytime” (or summer) lasts 42
years
When summer begins the Sun rises circles just above the
horizon, then for 21 years it gradually circles higher and
higher.
Finally it follows a circle about 8° from Zenith.
Then it spirals out, in larger and larger circles for 21 more
years
It only sets because of the change of seasons, and night (or
winter) lasts another 42 years!
The resulting unusual solar heating of the atmosphere may
explain the lack of cloud bands found on the other gas
giants.
Why Uranus is Tilted
Uranus’s extreme tilt is thought to be due to either:
• a collision with a large planetismal or
• the Gravity of nearby planets, mostly Saturn.
As a result of the extreme tilt at its “midsummer” a
Pole points nearly directly at the Sun.
Uranus Discovery and Rings
Uranus was unknown to the ancients. It was
discovered by Sir William Herschel in 1781
though at first he thought it was a comet
Uranus has has a complex
ring system like Saturn
But thinner.
In 1789 Herschel first saw
a ring but was unsure.
In 1977 the rings were
confirmed to exist
Uranus’ Moons
It has at least 27 Moons,
Including five larger ones
The two largest Titania and
Oberon were discovered
by Herschel
The Fifth largest, Miranda
seems to have been
shattered and then been
reassembled
Only 472 km in radius it has a giant cliff 15 km high!
That’s like one about 203 km (122 miles) high on
Earth!
The Discovery of Neptune
Neptune was unknown to ancients.
Galileo saw it in 1613 while looking at Jupiter’s
moons but didn’t know what it was
In the 1840’s two astronomers noticed a perturbation,
that is a slight change in Uranus’ orbit due to the
gravity of an undiscovered planet.
One was English …one French.
A German using the French calculations spotted it in
1846.
For decades both France and England claimed credit
for the discovery
Neptune
Neptune is a denser version of
Uranus. It has thin rings
It has more methane in its
atmosphere making it a deep
blue.
As it has a normal axial tilt it has
faint cloud bands
Winds on Neptune are
particularly fast 2200 km/h!
…powered by an internal heat
source.
Like Jupiter it has a large
That also makes it emit more heat
long lasting storm
than it gets.
The Great Dark Spot.
Triton and other Moons
Neptune has at least
six small moons.
The largest, Triton
orbits “backward”
And is probably a
captured Dwarf
planet from the
Kuiper belt.
It has a “wrinkled” cantalope-like terrain.
Geysers of nitrogen, water ice and carbon driven by
the Sun’s heat leave dark streaks like soot.
Voyager detected such an eruption