Astronomy 100 -- Outer Moons and Icy Bodies
SATELLITES OF JOVIAN PLANETS
The Galilean Satellites of Jupiter
By Size: Europa -- Io -- Callisto -- Ganymede
Compared to the terrestrial planets.
Io. Most volcanically active object
in the solar system.
Internal heat due to TIDAL FLEXING.
Europa. Has a very smooth,
slushy ice surface.
Ganymede. Largest moon in the solar system.
Actually larger than the planet Mercury.
Callisto.
Heavily cratered icy surface.
Surface is very dark with icy white impact craters.
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ORBITAL RESONANCES
These occur when there are integer relations between
periods of rotation and/or revolution of two objects.
For example:
- Mercury's rotation and revolution periods : 3/2
- The Moon's rotation and revolution periods : 1/1
- Pluto's rotation and Charon's revolution periods : 1/1
For the Galilean satellites, the revolution periods around
Jupiter are related:
- Io has an orbital period of 1.77 days.
- Europa has an orbital period of 3.55 days (2 times Io).
- Ganymede has an orbital period of 7.16 days (4 times Io
and 2 times Europa).
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There are
many small satellites of Saturn.
The six large Jovian satellites compared to the Moon.
Related Links of Interest
THE PLUTO-CHARON SYSTEM
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Basic Properties of
Pluto
1) Discovered in 1930 by Clyde Tombaugh.
Predicted to exist due to perturbations of the orbits of Neptune.
2) How old it it?
3) Where is it?
40 A.U. from the Sun, but a
highly elliptical orbit..
320 light-minutes from the Sun.
Are there other objects in the same orbit as Pluto?
4) What's it doing?
Rotation Period = 6.4 days and tipped like Uranus.
Revolution Period = 250 years.
Because of its distance from Earth and its small size, very little
was known about Pluto. But, Pluto was thought to be a very dense
planet as it was small yet pulled on Uranus and Neptune
(Made of solid gold?). We now know
much more about Pluto because of the discovery by James
Christy in 1978 of Charon, Pluto's satellite.
PROPERTIES OF THE
PLUTO-CHARON SYSTEM
- This system is a very low mass system.
Pluto = 1/500 Earth mass, 1/6 Earth diameter.
Pluto = 1/6 Moon mass, 2/3 Moon diameter.
Charon = 1/66 Moon mass, 1/3 Moon diameter.
Density of Pluto and Charon = 2 grams/cc, not that of gold.
Two properties can be implied from the low density:
1) Composition of both is mostly ice and rock.
2) Pluto is NOT perturbing the orbits of Uranus and Neptune.
Then what is? Planet X, Nemesis?
- Neither Pluto nor Charon has an atmosphere.
Solid frozen nitrogen surface.
Temperature = -220° C = 50K!
The Surface of Pluto,
takne by the New Horizons Satellite.
Large High Resolution Color Image of Pluto.
- Pluto and Charon are locked in SYNCHRONOUS ROTATION.
Period of 6.4 days for the rotation of each and the
revolution period of Charon.
Related Links of Interest
COMETS: Dirty Snowballs
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THE ANATOMY OF A COMET.
Fix Figure 15-18.
A) Nucleus - dirty snowball 1
to 20 km in diameter.
As the comet approaches the Sun, the nucleus heats up.
Inside 5 A.U., the following form and grow in size
as the comet approaches the Sun.
B) Coma - ball of outflowing gas and dust.
The diameter of the coma will be about 1 million km.
C) Tails - comets will have
two tails, which can be quite separate.
1) Dust tail [not affected by solar wind].
2) Plasma (or gas or ion) tail [affected by solar
wind].
These tails ALWAYS point AWAY from the Sun!
Fix Figure 15-20.
WHAT HAPPENS TO THEM?
Related Links of Interest
Gas Giants and Their Rings
Light and Radiation
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