Planets in the Outer Solar System

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Planets in the Outer Solar System
Scale Four Jovian planets mass,
size Density Compositions Interior
structures Jupiter from Earth Zones and Bands
Clouds Spot Magnetic Field Saturn Uranus Neptune
Pluto and Charon occultations (this class) Moons
and Rings (next class)
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The Outer Solar System
Inner Solar System Sun-Mercury 0.4 AU Sun-Mars
1.5 AU Outer Solar System 30 times
larger Sun-Jupiter 5 AU Sun-Pluto 39
AU
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The four Jovian Gas Giant Planets
Large Massive Gaseous no solid surfaces
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Density tells us the bulk composition
Density Mass/volume. Depends on composition and
compression by gravity. Inner planets are rocky
with varying amount of iron in core.
Jupiter and Saturn are mostly H and He
Uranus, Neptune, and especially Pluto are ices
Iron 8 g/cm3 Rock 3.5 g/cm3 Ices 1.5
g/cm3 Gases 1 g/cm3
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Compositions
The Jovian planets are very different from the
terrestrials. Jupiter is like the sun Hydrogen,
with some Helium and a small core with heavier
elements (C, N, Si,) Saturn has a larger of
heavier elements. Uranus and Neptune are mostly
CH4, NH4, H2O molecules that form ices when
refrigerated but they are compressed gases
(atoms do not have fixed neighbors) inside these
planets.
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Compositions of Jovian Planets
Who has the most water as compressed gas not
liquid?
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Pressure stops a gaseous planet from collapsing
Hydrostatic equilibrium is the balance of
pressure and gravity in all gaseous bodies,
planets and stars. The inside has higher
pressure to support the material on top. The
pressure comes from the temperature and density,
both increase towards the center.
Cold atmosphere Hot inside. 20000K for Jupiter
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Interior Structure
Jupiter and Saturn have similar structures. Both
still slowly shrinking.. Helium is falling to
center, faster than hydrogen. Gravitational
energy released makes them radiate more infrared
energy than they get from the Sun.
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The Interior of Uranus (and Neptune)
Uranus and Neptune, like J and S, are entirely
gaseous. They have much smaller H and He
envelopes of J and S. They have higher densities.
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Jupiter from Earth
Can be brighter than any star. Easily see bands
in atmosphere and 4 moons with a 10 inch
telescope
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Jupiter King of the Planets
9.9 hours (Jupiter's day) makes bands of
alternating wind directions.
zones lighter, rising, warm gas
belts darker, falling, cooler gas.
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Banded Structure of Clouds
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Atmospheres of Jupiter and Saturn
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Great Red Spot
gt300yr old cyclone the size of the Earth
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Red Spot Movie
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Making Magnetic Fields not Midterm1
Magnetic field arises when there is a conducting,
convecting medium in a rapidly rotating body.
This dynamo makes the field.
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Jupiters Magnetosphere Bigger than the Sun
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Auroral Zones
The high energy particles come down the field
lines and hit the atmosphere near the poles,
causing the gases to glow. As for our Earth, this
makes aurora in a ring-like zone visible in
ultraviolet.
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Saturn
Mass 95 Earths, Radius 9.4 Earths, density
0.7 x water (floats) Distance 9.5 AU Orbital
Period 29.4 years Rotation period 10.6
hours. Movie shows rings from 1996-2000
http//hubblesite.org/newscenter/archive/2001/15/

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The Cassini Mission at Saturn 2004
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Uranus from Earth
William Herschel discovered 1781 in a systematic
survey of sky with telescope. Sometimes barely
bright enough to see without telescope. With
small telescope see disk and moons.
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Uranus from Nearby
Mass 14.5 Earths, Radius 4.0 Earths, density
1.3 x water Distance 19.2 AU Orbital Period
84 years Rotation period 17.2 hours. Movie
shows moons, ring wobble and seasonal changes in
methane (?) clouds. http//hubblesite.org/newscent
er/archive/1999/11/
visible
ultraviolet
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A Very Tilted Pole
The seasons on Uranus are extreme. Half the
planet shares the fate of the pole in not seeing
the Sun for half the Uranus year (40 years).
Nonetheless, the temperature is fairly uniform
around the planet the gases redistribute the
heat.
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Neptune
Discovered 1846 at the position calculated from
the deviations it causes in Uranuss orbit.
Voyager showed it is more like Jupiter than
Uranus in appearance. Adaptive optics images
form Earth show storms in infrared.
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Clouds and Storms on Neptune
High clouds are made of methane ice crystals. The
heat flow is greater than expected, giving more
storms. The Great Dark spot was an upwelling, now
gone. Movie shows clouds brighter 1996-2002 as
South pole heats up in Spring. http//hubblesite.o
rg/newscenter/archive/2003/17/
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Pluto from Earth
Discovered in a survey in 1930 by Clyde Tombaugh
in Arizona. Pluto was closer than Neptune from
1989 1999. Pluto is hard to see in a small
telescope, and only just resolved (0.1 arcsec)
with adaptive optics on a large telescope.
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Pluto
From Pluto, the sun is unresolved by eye. Below
is an imaginary view. NASA would like to send a
mission but lacks funds.
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Pluto and Charon tidally locked double Planet

Charon is half the size of Pluto and it is close
to Pluto, in terms of their radii like a double
planet. Strong tides, because close together.
Tidally locked periods Plutos day 6.387
Earth days Charons day6.387 Earth days Charons
orbital period 6.387

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Pluto and Charon surface features

From 1985-1990 Charon and Pluto occulted
(covered) each other, giving crude surface maps
that show a lot of contrast.

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Pluto and Charon occultations

An occultation (Pluto passes in front of a star)
in 1985 showed that Pluto has a thin atmosphere,
probably nitrogen and methane
Plutos atmosphere will freeze out onto its
surface as it recedes from the Sun. The path of
Pluto's shadow in 2002 (grey region) is shown
projected on to South America. The shadow moves
from right to left in about 5 minutes.
www.astro.virginia.edu/.../ astr121/notes/pluto.ht
ml

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Pluto might look like Triton
Neptunes moon Triton is likely a good model for
Pluto.