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Chapter 11
Survey of Astronomy
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JUPITER – Lord of the Planets
To discuss the Jovian Planets we must first talk
about The Voyager program. The mission of
Voyager 1 & 2 is to visit the Outer Solar System and
beyond.
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This is the Voyager 2 velocity profile showing the velocity flips
at each planet. Our booster was barely able to reach Jupiter without gravity
assist. With
gravity assist
we have left
the Solar
System
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Jupiter can be imaged well from Earth, even with a
small telescope
Here: Jupiter with its Galilean moons
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Earth
Pioneer
1973
Voyager
1979
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•Mass: More than twice as much as all other
planets put together.
• Radius: 11.2 times Earth’s radius
• Density: Only 1.3 x the density of water – cannot
be rocky or metallic as terrestrial planets are
• Rotation Rate: problematic, as Jupiter has no
solid surface; different parts of atmosphere rotate
at different rates. The solution came from
magnetic field, whose rotation period is 9 hr, 55
min
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Early images of Jupiter
showed the Great Red
Spot and Stripes. As our
instruments improved
many more details
emerged. The spot
became a giant storm
and stripes became
bands of rising and
falling gases.
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The colors have changed over the
years from brick red to light brown.
The size has changed from 3x the
size of the Earth to just over 2x.
Voyager -Visible
It seems to be and inverted storm
dipping to the planet rather that
rising above it.
Galileo-Infrared
Great Red Spot has existed for at
least 300 years, possibly much
longer.
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The Atmosphere has bright
zones and dark belts. Zones
are rising warmer gasses
from the interior, and are
higher than belts. The Belts
are cooler falling gases
returning to be re-warmed.
The many storms seen in the
belts are due to turbulence
caused by differential
rotation in the atmosphere
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The composition of the Atmosphere is
mostly molecular hydrogen and helium
with small amounts of methane,
ammonia, and water vapor. The
impurities seem to account for the
colors, probably due to complex
chemical interactions that we are still
studying
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No solid surface; take top of
troposphere to be 0 km
The lowest level of the
atmosphere is the stripes.
Telescopes can not see
through it.
Measurements by Galileo
probe show high wind speeds
even at great depth –
probably due to heating from
inside the planet, not from
Sun
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Great Red Spot has existed for at least 400 years, possibly
much longer
Color and energy source still not fully understood
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Lightning-like flashes
have been seen; also
shorter-lived rotating
storms
One example: Brown
Oval, really a large gap
in clouds
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We find that Jupiter radiates more energy than
it receives from the Sun:
Core is still cooling off from heating during
gravitational compression.
Could Jupiter have been a star?
No; it is far too cool and too small for that. It
would need to be about 80 times more
massive to be even a very faint star
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No direct
information is
available about
Jupiter’s interior, but
its main components,
hydrogen and
helium, are quite
well understood. The
central portion is a
rocky core.
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Jupiter is surrounded by belts of charged particles, much like
the Van Allen belts but vastly larger Magnetosphere is 30
million km across
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Intrinsic field
strength is 20,000
times that of Earth
Magnetosphere
can extend beyond
the orbit of Saturn
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More than 60 moons have now been found
orbiting Jupiter, but most are very small.
The four largest are the Galilean moons, so
called because they were first observed by
Galileo:
• Io, Europa, Ganymede, Callisto
Galilean moons have similarities to terrestrial
planets; orbits have low eccentricity, largest is
somewhat larger than Mercury, and density
decreases as distance from Jupiter increases
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The Small moons
move in mostly
eccentric orbits far
from Jupiter. Here,
the orbits of the
Galilean moons
can be seen in the
center near the
planet.
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These are the Galilean moons. Each is unique.
Each is interesting.
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The Galileo Probe has given
us a very good feel for their
interiors
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Io is the most dense of Jupiter’s moons, and the most
geologically active object in the solar system. It has many
active volcanoes, some quite large. It can change surface
features in a few weeks There are no impact craters; they
fill in too fast – Io has the youngest surface of any solar
system object.
The many colors come from sulfur at different temperatures
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The vulcanism on Io is due to tidal forces. Io is
very close to Jupiter in a rather eccentric orbit,
and also experiences gravitational forces from
Europa and Ganymede. The tidal forces are
huge and provide the energy for the Volcanoes.
This image of Io is
the discovery image
for the volcanos
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Volcanic eruptions also eject charged
particles; these interact with Jupiter’s
magnetosphere and form a plasma torus
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The moon Europa has no impact craters, The surface
is water ice, likely with liquid water below
Tidal forces stress and crack the ice allowing liquid
water to flow out keeping surface glass smooth
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Ganymede is the largest moon in the solar system –
larger than the planet Mercury
Impact history similar to Earth’s Moon, but water
ice and dirt instead of lunar rock
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Surface areas of Ganymede once thought
to be cratered and flat turn out to have
structures. These may be due to a form of
plate tectonics
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Calisto is similar to Ganymede except
there is no evidence of plate activity.
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One of the big surprises of the Voyager
program was the discovery of a ring around
Jupiter. This is the discovery image.
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These four moonlets are associated with
Jupiter’s ring. The two tiniest, Metis and
Adastria are embedded in the ring and seem
to be shattering to feed the ring. The other
two, Amalthea and Thebe, are “Shepherd”
moons.
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This image made by the Galileo spacecraft
shows more details. Especially evident are
the sharp outer edge and the diffuse inner
edge of the ring and the detail within the
rings are explained by the presence of the
moonlets.
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