Neptune – Poseidon: God of the sea.
Need a telescope; Galileo saw it in 1613 and thought it
was a star (whose position somehow changed...); Predicted from
perturbations of Uranus' motion, and identified as a planet in
Radius about 30 AU, almost circular [eccentricity 0.01, period
165 years]; sometimes [for example between
1979 and 1999] actually more distant than Pluto.
- Planet: A gas ball 4
times the Earth's size [17 times the mass, 1.7 times
the density of water], a little smaller and more massive than Uranus.
Visited only by Voyager 2 (in 1989), which now is more than 90
AU from the Sun, leaving the Solar System; Some teams are planning future
missions to Neptune and Triton.
Bluish from methane (more than Uranus), cloud bands and
spots; the strongest atmospheric circulation of all the gas giants!
- Rotation: The atmosphere rotates
once every 17.3 hrs (the interior rotates faster, but the planet
is not very flattened); tilted 30° with respect to the orbit
- Surface features: More cloud
features than Uranus, because it is heated from below, like Jupiter
and Saturn; Great Dark Spot (seen by Voyager, gone by 1994).
- [Interior: Molten rocky core,
Earth-sized; The rest is a mix of water, ammonia, methane.]
Moons and Rings
At least 14 (the last one was reported in 2013); The
largest one is Triton (larger than Pluto), on a retrograde orbit,
with active ice volcanoes, and the only one with a known atmosphere,
other than Saturn's Titan; Nereid is medium-sized, the other
ones are small.
3 narrow ones, 1 wide one, made of microscopic dust; The
outermost ring (Adams) consists of 5 short arcs, that are kept
from dispersing by the nearby moon Galatea.
page by luca bombelli <bombelli at olemiss.edu>,
modified 15 jul 2013