The Giant Planets: Jupiter, Saturn, Uranus and Neptune
A basic introduction to Jupiter is on : go
to Arizona LPL Jupiter link.
Jupiter's composition is mostly hydrogen and helium :
The interiors of Jupiter and Saturn are composed of layers, including molecular hydrogen on the outside, liquid metallic hydrogen intermediate, and at the center a rocky core which resembles a terrestrial planet.
Liquid metallic hydrogen is an extreme state of hydrogen, that we do not have on earth. The very high pressure in the interiors of Jupiter and Saturn squeezes the hydrogen atoms into a metallic state, but still liquid, rather like the mercury in a thermometer on earth.
Jupiter shows dramatic cloud structure, including bands
that go around the planet driven by high winds. A curious feature
in the clouds is the great red spot:
Jupiter also has a strong magnetic field, that traps a huge magnetosphere. Here is a radio image from the VLA :
Galilean Satellites of Jupiter
Jupiter has many moons (28 is the most recent count),
but the four largest are worlds in themselves. Discovered by Galileo
with his primitive telescope, these moons can almost be seen by eye, and
they are easy to see with binoculars or a small telescope. Their
properties show the striking effect of tidal dissipation of energy, that
heats their interiors. Moving out from Jupiter (from the strongest
to the weakest tidal dissipation) we find Io, Europa, Ganymede, and Callisto.
Io is the most geologically active object in the entire solar system.
It is covered with volcanoes, constantly emitting sulfer lava and gas.
Left is visible light, right infrared, that traces the hot spots:
The volcanoes erupt sending plumes of gas far into space,
because Io has no atmosphere. Here is a nice view:
Here is a sketch:
A global view:
Here is a very recent image of Io from the astronomy picture
of the day site :
go to APOD Io image.
Europa is the next large satellite out from Jupiter. It has an ice crust, and likely a liquid water ocean below the ice:
Ice rafts are similar to those on the arctic ocean on earth:
Ganymede is the next. It also has an icy crust and
may have a liquid ocean below:
And finally Calllisto. It has the oldest surface,
with many many impact craters.
Here are more images of the Galilean Satellites, and of
to NSSDC images page.
And here is a more detailed discussion : go to NASA JPL planetary news page.
Saturn's most dramatic feature is its rings:
Saturn's largest moon, Titan, is interesting for its nitrogen
atmosphere, and surface pressure similar to the earth's:
The NASA / European Space Agency's probe Huygens will explore Titan next year. Above is an artist's conception of its lander parachuting through the atmosphere.
Continue to Uranus
and Neptune page.