Chapter 8
Jupiter
- known since ancient times
- Named for
the King of the Gods (but why?)
- In
appearance, Jupiter is slightly flattened due to its gaseous nature and
high speed of rotation.
- Jupiter is
completely covered by clouds and has no solid surface.
- Light
zones and dark belts encircle the planet, giving it a striped
appearance. the zones are areas of rising atmosphere, whereas the belts
are falling atmosphere.
- Numerous
oval shaped cloud patterns can be seen, including the enormous Great
Red Spot, which is something like an "anti-hurricane" that can be
nearly three times the diameter of Earth. (Unlike earthly hurricanes,
which are low pressure cells, the Great Red Spot is a highpressure
cell.) It has faded considerably in recent years.
- Jupiter is,
on the average, 5.2 times the Earth's distance from the Sun.
- Jupiter is
huge, 11 times the diameter of Earth or about 143,000 km (roughly
88,000 miles)
- In mass, it
is 317 times the mass of Earth, or more that all the other planets
combined.
- In
composition, it is really more like a star than a planet.
- Composed
mostly of Hydrogen and Helium
- Thick
gases get thicker the deeper you go, and pressure rise dramatically
- At the
visible surface of Jupiter -- the cloud tops -- the temperature is
about 125 K or 235
d below zero F.
- At about
7000 km down, pressures have risen to 500,000 times that at the surface
of Earth, and the temperature is 2000 K -- hotter than a blast furnace.
Due to the pressure, hydrogen becomes liquid here.
- At a depth
of 14,000 km, pressure is 2 million times that at the surface of Earth,
temperature is nearly that of the surface of the Sun (5000 K), and
hyddrogen becomes "metallic"
- At 60,000
km and 100 million atmospheres, Jupiter probably has a "small" core
(still larger than the whole Earth) of rock, metals and hydrogen
compounds. Temperature of the core is 20,000 K, more than 3 times that
of the surface of the Sun!
- Due to its
internal heat, Jupiter radiates more energy into space than it receives
from the Sun. Some of this energy goes into powering the complex
weather patterns on the planet. Other energy is radiated away as radio
waves and other electromagnetic energy. The planet also has an
enormously strong magnetic field thought to be produced by free
electrons accelerating in the metallic hydrogen interior.
- Jupiter has
a retinue of at least 63 natural satellites or "moons."
Except for Io, these are all icy worlds.
- Four Moons
are large enough to be seen with a small telescope of pair of binoculars
- Io
("Eye-oh") is the closest large moon to Jupiter. About the size of
Earth's Moon, Io is subject to great tidal forces from Jupiter. This
heats and melts subsurface layers, forming volcanoes. Io is the first
(and so far only) body in the Solar System
to show currently active volcanoes. "Fire
and brimstone, thy name is Io." Neptune's Triton has what may be called
"ice geysers," but that are not the same. Io's volcanic nature makes it
an exception to the rule that most moons of outer planets are covered
with ice, and fairly frequent flows of lava erase the evidence of
impacts (it has virtually no impact craters visible.) There are a
number of factors contributing to Io's volcanic activity, not the least
of which is the enormous gravitational force of Jupiter, which exerts
strong tidal forces on nearby Io. Other factors include gravitional
tugs from other moons (especially Europa), possibly its own internal
heat, and Io's elliptical orbit that strengthens the tidal flexing.
- Europa
is an ice-covered world slightly smaller than our Moon. Apparent
movements in its icy crust point to a possible ocean of liquid water
underneath. Europa is considered one of the best places in the Outer
Solar System to look for life.
- Ganymede
is the largest planetary satellite in the Solar System, being larger
than the planet Mercury. It has a complex and icy surface geology with
strange features possibly related to a warm core (the possible evidence
for which is the fact that it has a magnetic field). There is a slight
chance of an ocean under the ice, but this is highly speculative.
- Callisto
is very slightly smaller than Mercury. It is an icy world largely
covered with craters and some areas covered by a material darker than
ice. Like Ganymede, Callisto may have a small magnetic field, possibly
giving evidence of a slight internal heat source and/or a salty ocean
beneath the crust -- but this is also highly speculative.
- The at
least 59 other moons are icy and small, with only a couple more than
100 kilometers in size, and most only a few kilometers across.
- Some of
the larger satellites ("moons") of Jupiter and the other Gas Giants are
roughly spherical, which says that their gravity is strong enough to
pull them into that shape. Smaller moons are irregular in shape because
they do not have enough gravity to overcome the electromagnetic forces
that bind them together.
- Most moons
of Jupiter and the other Outer Planets show many impact craters and in
some cases evidence of crustal movement in cracks and fissures.
Movement of ice is a major force in shaping the face of these worlds,
and in some cases helps to erase the effects of previous changes.
Jupiter's Io is an exception due to its volcanic surface.
- Unknown
until discovered by Voyager I in 1979, Jupiter has a faint, thin ring
which could be composed of particles from Io's volcanic emissions.
·
Saturn
- Much of
what has been said about Jupiter applies to Saturn as well.
- It is
nearly twice as far from the Sun, at about 9.57 AU.
- Saturn
is about 121,000 km in diameter (about 75,000 miles)
- It is
about 95 times the mass of Earth. (It's density is about 70 percent
that of water)
- It's
structure is similar to Jupiter's, but because it is considerably less
dense, it likely has less metallic hydrogen.
- It has a
magnetic field, probably due to the motions of free electrons in the
metallic hydrogen core, but it is much less than that of hydrogen
- The Ring
System, by far the most spectacular among the planets,is composed of
ice fragments that range in size of microscopic to the size of small
boulders. Recent evidence suggests that some may be larger, and that in
some rings the particles are "clumped" together rather than evenly
spread out.
- Saturn
currently has 35 named moons, with probably more small ones to be
discovered.
- Most
are small, with only 5 larger than 1000 km in diameter
- The
largest is Titan, larger than Mercury and the second largest moon
behind Ganymede
- Titan
has a nitrogen atmosphere with an atmospheric pressure 1.5 times that
of Earth
- Titan
is covered with clouds, and may have an ocean of methane or ethane
- It
is thought that there may be some chance of life on Titan
- Some
small Saturnian Moons are close enough to the rings -- within the rings
in some cases -- to exert a gravitational force on them, causing them
to have gaps in places. Others cause the shapes of the outer rings to
be warped or "braided."
·
Uranus
- Uranus
is about 19.1 AU from the Sun, nearly twice the distance of Saturn
- Uranus
is smaller than Jupiter or Saturn, at about 51,000 km (32,000 miles) in
diameter
- Uranus
is only 14.5 times the mass of the Earth (It's density is about 1.27
times that of water)
- Uranus
likely has no metallic hydrogen, but water, ice and a small core of rock
- Uranus'
axis of rotation is tilted to the plane of its orbit, as if it were
"laying down."
- It has a
magnetic field, oddly tilted to its rotation axis
- It does
not emit much energy into space, and likely does not have a strong
source of internal heat
- Uranus
has at least 21 moons, 5 of which are 1000 km or more in diameter
- Uranus
also has a thin set of rings
·
Neptune
- Neptune
is very similar to Uranus in most respects
- It is
nearly 30 AU from the Sun, about 50 percent farther than Uranus
- It is
slightly smaller (49,500 km) and denser (1.64) than Uranus
- Like
Uranus, Neptune likely has no metallic hydrogen, but water, ice and a
small core of rock
- Also
like Uranus, Neptune also has a magnetic field, oddly tilted to its
rotation axis
- Neptune
has at least 13 satellites, all small except Triton, which is 2700 km
in diameter
- Triton
has a very interesting geology and "ice volcanoes" or "ice geysers" and
"cantaloupe terrain"
- Icy
Triton may bear a strong resemblance to Pluto
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