Astronomy 330

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Astronomy 330

• Lecture 19

http//www.nasa.gov/mission_pages/cassini/multimed
ia/pia06197.html
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Astronomy 330 Notes on Formation of Jovians

• The predicted amounts of elements were based on
  the idea that Jupiter and Saturn should be the
  same as the comets.
• Comets are deficient in N relative to C, O, and S
  as seen on the Sun.
• So it is surprising that the elemental abundances
  for ALL the elements are enhanced by a factor of
  3 compared to the Sun. (Except for He which
  precipitates out as we have seen and Ne which
  also dissolves in liquid He).

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Astronomy 330

• So, Jupiter at least, seems to be enriched in
  heavy elements relative to its H content.
• No solid objects in the Solar System shows this
  characteristic.
• If Jupiter formed by first accreting icy
  planetesimals (i.e. comets), these planetesimals
  must have formed below 38K to trap gases like Ar
  and N from the Solar Nebula.

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Astronomy 330

• Such a low temperature is surprisingbecause this
  temp. corresponds to the outer Solar System (near
  the orbit of Neptune), not where Jupiter and
  Saturn are.
• Also, since the cores of all the Jovians are
  10-15 times the mass of the Earth, the icy
  planetesimals with near solar composition must
  have been the most abundant form of matter in the
  early history of the Solar System.

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Astronomy 330 Weather and Climate

• Complicated !!!
• Bands in Jupiters clouds and easily be seen
  using a small telescope.
• This indicates there must be different kinds of
  clouds at different levels
• Many of the color changes seen on Jupiter are
  actually due to changes in depth in the
  atmosphere.

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Astronomy 330 Atmospheric Bands on Jupiter and
Saturn
http//solarsystem.nasa.gov/multimedia/display.cfm
?IM_ID1749
http//www.nasa.gov/mission_pages/cassini/multimed
ia/pia06197.html
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Astronomy 330

• Changes in the cloud bands are observed to take
  place over the space of a few hours.
• Spacecraft observe that the clouds are constantly
  shifting and changing
• The mains features are the bands which indicate
  flows parallel to lines of latitude.
• Saturns clouds and bands are much more difficult
  to see.

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Astronomy 330 Galileo approaches Jupiter
http//solarsystem.nasa.gov/planets/index.cfm
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Astronomy 330 Winds and Rotation

• Jupiter and Saturn have 3 rotation speeds !!!
  (These are actually averages at the equator and
  at higher latitudes and the interior).
• System I (equator) - 9h50m (J), 10h14m (S)
• System II (high lat.) - 9h55m (J), 10h40m (S)
• System III (deep interior) - 9h55m (J), 10h39m
  (S)
• Rotation periods are defined by measuring motions
  of the movement of features in the clouds (no
  solid surface, so these periods are somewhat ill
  defined)

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Astronomy 330

• Also, studies of radio emission show an
  unchanging periodicity due to its rotating
  magnetic field and this defines the interior
  period of rotation (system III).
• This was confirmed by Voyagers and Galileo
• Using System III as a standard, Jupiter shows an
  eastward flowing equatorial jet stream of about
  360 km/hrsimilar to the Earth.
• At higher latitudes, alternating bands of
  westward and eastward winds are detected on
  Jupiter.

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Astronomy 330 Jupiters cloud bands in motion
http//solarsystem.nasa.gov/planets/index.cfm
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Astronomy 330

• On Saturn the clouds are much more uniform.
• Spots sometimes appear that can be seen from
  Earth.
• An equatorial jet is also present and extends to
  /- 40o N and S and its velocity is 1,600 km/hr!
• At higher latitudes, alternating bands of winds
  appear.

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Astronomy 330 Comparison of cloud systems on
Jupiter and Saturn
False color enhanced from Cassini in infrared.
Voyager 1
http//solarsystem.nasa.gov/planets/index.cfm
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Astronomy 330 General Circulation

• These differences do not yet have a good
  explanation
• A theory The circulation patterns go very deep
  into the planets, and the patterns that we see
  may be the tops of cylinders of fluid which
  rotate about the rotation axis of the planet. In
  this theory, the interiors of the planets play a
  role in shaping the outer, observed cloud bands.

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Astronomy 330

• Comparing these circulation patterns to Earth we
  see that Earth has large spiral clouds features
  (cyclones) associated with low pressure
  features.Clouds on Earth move from latitude to
  latitude as well as moving in longitude.
• This type of motion (latitude to latitude) does
  not happen on Jupiter or Saturn.
• Using global circulation computer models of the
  gas giant planets (similar to those used for the
  Earth) which take into account the large masses
  and faster rotation, show that disruptive eddies
  are much smaller (relative to the size of the
  planet) and east-west bands of winds are much
  more stable.

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Astronomy 330

• High rotation rate is a factor in circulation
  patterns.
• So is the lack of a solid surface. This also
  contributes to the stability of the banded
  features. This has the effect of eliminating the
  equator to pole temperature difference seen on
  Earth which drives the creation of the cyclones
  and eddies.

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Astronomy 330 Schematics of Belts and Zones
http//www.windows.ucar.edu/tour/link/jupiter/jup
iter_il.htmleduhigh
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Astronomy 330 The Red Great Spot and a white oval
Note the white ovel has been present for about
40 years.
http//solarsystem.nasa.gov/planets/index.cfm
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Astronomy 330

• Has existed for at least for 170 (maybe 300)
  years and can be seen telescopically from Earth.
  We think Galileo may have observed it as well.
• It is 18,000 by 12,000 km, Earth could easily fit
  in it.
• It is unknown exactly what it is. The clouds
  inside it exhibit a counter-clockwise rotation
  with a 6 day period. So, it is a huge
  anti-cyclone (a vortex with a high pressure at
  its center).

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Astronomy 330

• Voyager and Galileo failed to detect any
  upwelling at the GRSs interior.
• The clouds appear to be very well ordered and
  tranquil in the spots center.
• On Earth cyclones only last for a few days and
  are associated with white, water clouds.
• The GRS stick out above the other clouds
  surrounding it, but how far down it goes is
  unknown. It also unknown what the composition is
  which gives it its red color.

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Astronomy 330 Ovals, brown spots and hot spots
View of three ovals which merged. Ovals formed
in 1930s.
http//photojournal.jpl.nasa.gov/
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Astronomy 330 A brown oval on Jupiter
http//www.windows.ucar.edu/tour/link/jupiter/ima
ges/lboval_image.htmleduhigh
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Astronomy 330

• Many circular or oval cloud features are seen on
  Jupiter which are smaller than the GRS.
• Also, these features show different colorswhite
  and brown spots.
• Brown spots are holes showing deeper, brown
  colored, layers in the atmosphere and are found
  always at latitudes near 18o N.
• Blue grey areas show the strongest thermal
  emission and are known as hot spots and occur
  ONLY in the equatorial regions.

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Astronomy 330

• The equatorial hotspot are clear air that allow
  us to see deep into Jupiters atmosphere.
• We know this from the intense thermal radiation
  coming from these spots. They are the brightest
  spots on the planet (from Galileo).
• Galileo probe descended into one of these hot
  spots and found no thick cloud layers.
• When we say hot spot we mean that we are seeing
  the hot, deep regions of the atmosphere even
  though Galileo passed through cold, dry air.

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Astronomy 330

• It is still unknown why the meteorological
  features occur at particular latitudes.
• One characteristic is the large the feature, the
  longer it lasts.
• On Earth, hurricanes die when they pass over
  land.
• No land on Jupiter, so they can persist and the
  large they are, the less susceptible they are to
  other disturbances.

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Astronomy 330

• Since Jupiter and Saturn have strong source of
  internal heat, we expect them not to show
  seasons.
• On Jupiter this is true.
• Also, the Galileo probe showed that high winds of
  the equatorial jet stream continue deep (20 bars)
  into the atmosphereconsistent with internal
  heating. On Earth the jet is driven by Solar
  heating.

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Astronomy 330 Cloud Colors and Chemistry

• Condensation clouds - water vapor condenses into
  droplets or ice crystals. Clouds on Earth.
• Dust clouds - Like on Mars and Earth.
• Photochemical haze - smog, produced by chemical
  reactions and UV rad.
• Jovians can produce only condensation and
  photochemical clouds.

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Astronomy 330

• On Jovians, with their H rich atmospheres and
  other elements, it is very easy to form
  photochemical hazes.
• These hazes are organic (compounds of C) in
  nature.
• Surprisingly, on Jupiter and Saturn
  photochemistry and solar heating of the upper
  stratosphere is very important.
• Temperature increases above the tropopause due to
  Solar UV heatinga thermal inversion (where the
  temperature increases when it should be
  decreasing).

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Astronomy 330

• All four gas giants show this temperature
  inversion effect and it is caused by the
  efficient absorption of UV radiation by H and
  other chemicals.
• On Earth the temperature inversion is caused by
  the presence of Ozone absorbing UV light.
• On Jupiter and Saturn hydrocarbons form in the
  upper atmosphere above the inversion.

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Astronomy 330

• Jupiter and Saturn do not reflect UV and blue
  lightthey absorb them.
• Hazes are thin since there is so much H.
• Hazes are composed of very small
  particlesaerosols.
• These aerosol particles sink and are converted
  back to simple substance by the internal heat of
  these planets.

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Astronomy 330 Condensation clouds

• Highest and coldest condensation clouds are
  composed of ammonia and white cirrus-like clouds.
• The next cloud layers are light brown and
  indicate a chemical change. Could be ammonium
  hydrogen sulfide, but this is white in color and
  some other chemistry must be occuring here.
• Remember, Galileo probe descended through a clear
  spot and did not make direct measurements of
  these clouds.

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Astronomy 330

• At even lower levels, water clouds form.
• Not pure water, but will contain ammonia also and
  other soluble gases.
• Water clouds mean lightning and lightning has
  been detected on Jupiter.
• Lightning is a telltale sign that there are water
  clouds on Jupiter.

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Astronomy 330 Chemical clouds

• The light brown clouds probably have something to
  do with the chemistry of Sulfur since S can
  combine with itself to form brown, light brown or
  yellow compounds.
• Other sulfur compounds are also brown
• Phosphorus forms red compoundsmaybe in the GRS?
• Phosphorus can also from yellow compounds (e.g.
  PH3) and may be present on Jupiter and especially
  Saturn.

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Astronomy 330

• Other organic compounds produced by reaction of
  methane and ammonia are also know to be reddish
  in color.
• What we have said about coloring is all theory
  based on experiments on Earth which simulate the
  composition of Jupiter and Saturn and subject
  these chemicals to electrical discharges and UV
  radiation.
• But, exactly what is going on it unknown since
  these chemicals do not have easily detectable
  spectral features. Need direct probes.

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Astronomy 330 Different clouds at different
heights
Saturn
Jupiter
http//www.windows.ucar.edu/
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Astronomy 330 Impacts (on a gas giant?)

• Comet S/L 9, roughly 20 pieces smashed into
  Jupiter in July 1994.
• Each penetrated below the ammonia clouds and
  disintegrated and then exploded.
• Post impact observations showed only a small
  amount of water ejected, so the comets pieces
  exploded above the depth where the water clouds
  are (at about 5 bars).
• Each piece produced a fireball which ejected
  comet material and Jupiter atmosphere into the
  stratosphere and it spread over many km.

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Astronomy 330

• The impact produced dark clouds which include
  much C and S.
• Dark clouds disappeared over the course of the
  next several months.

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Astronomy 330 Comet SL 9 impacts Jupiter
http//www2.jpl.nasa.gov/sl9/top20.html
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Astronomy 330 Magnetospheres

• Review of the Earths magnetosphere
• Caused by interaction of Solar Wind in Earths
  magnetic field
• Teardrop-shaped.
• Charge particles trapped in belts, VanAllen
  radiation belts.

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Astronomy 330

• Jupiter and Saturn each have VERY strong magnetic
  fieldswe expect them to have magnetospheres as
  well.
• Jupiter was the first planet observed to observed
  to be a radio source (at 20 Mhz, 15 m).
• Produced by the interaction of charged particles
  with the magnetic field of Jupiterthis is called
  synchrotron radiation and is a form of
  non-thermal radiationradiation not due to heat
  of an object.

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Astronomy 330

• Sometimes Jupiter is the brightest source for
  these radio emissions (except for the Sun) and
  these longwave emissions come in bursts.
• This is also the first evidence that was obtained
  that Jupiter had a magnetic field.
• Jupiter is also a source of steady radio emission
  at wavelengths shorter than 1 m.
• This shorter wavelength radiation is due
  primarily to electrons trapped in Jupiters mag.
  field in belts as at Earth.

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Astronomy 330 The Magnetosphere of Jupiter seen
in Radio
http//www.windows.ucar.edu/tour/link/jupiter/ima
ges/jupiter_radio_image_jpg_image.html
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Astronomy 330

• Jupiter also has a belt of trapped protons
• These radiation belts are similar to Earth, but
  larger and more dense.

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Astronomy 330 Effect of IO on magnetosphere

• Radio noise storms at long wavelengths are
  influenced by the position of IO.
• IO is the closest Galilean satellite.
• Radio is enhanced when IO and Jupiter make a 90o
  angle with the earth.
• IO is linked be a magnetic flux tube (a cluster
  of parallel magnetic field lines) which connects
  it to Jupiter.
• As IO moves, it drags the foot of this flux tube
  across the face of Jupiter.

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Astronomy 330

• Electrons spiraling in the flux tube and
  interacting with the ionsphere of Jupiter cause
  the radio outbursts.
• A 5-million Amp. Current is flowing through the
  flux tube at any one time and is generated by IO
  moving through the magnetic field of Jupiter.
• IO (which has active volcanoes) also produce
  heavy ions and injects them into the inner
  magnetosphere of Jupiter creating what is called
  the IO plasma torus.

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Astronomy 330 The IO Sulfur torus
http//www.windows.ucar.edu/tour/link/jupiter/ima
ges/Io_sulphur_torus_jpg_image.html
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Astronomy 330

• It has been recently dicovered that the Moon
  Europa also causes a neutral gas torus to form.

http//photojournal.jpl.nasa.gov/catalog/PIA04433
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Astronomy 330

• The spacecraft which have visited Jupiter have
  also taken detailed measurements of its magnetic
  field.
• It is dipolar, like a bar magnet.
• It is generated by a natural dynamo at the center
  of the planetnot from molten iron, but from
  liquid, metallic hydrogen.
• The strength of the field is 19,000 times greater
  than that of Earth.
• The orientation of the field is currently
  opposite to the of the Earths.

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Astronomy 330

• Saturns field is weaker and shows that same
  orientation as Jupiters.
• Unknown if these fields reverse like the Earths.
• The field of Saturn is not inclined relative to
  its rotation axis like the Earths and Jupiters.
  Dynamo theories predict that there should be
  some inclination so this is surprising.

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Astronomy 330 Saturns Radio Emission

• Saturn does not show strong radio emission as
  Jupiter does.
• Voyager was the first to detect long wave radio
  from Saturn (3 KHz to 1.2 Mhz and peak is a
  wavelengths of 2 km).
• Earths ionosphere reflects such
  wavelengthsthats why we never detected them
  before Voyager.

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Astronomy 330

• Energy for Saturns radio emissions comes from
  electrons from the Sun interacting with its
  magnetic field.
• Changes in the Solar wind therefore cause large
  changes in radio.
• This interaction was used to measure the rotation
  of the inner parts of the planet we talked about
  earlies.

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Astronomy 330 Van Allen belts

• Both Jupiter and Saturn are surrounded by LOTS of
  plasma (remember what plasma is?).
• Three sources for plasma
• Solar wind
• Atmospheres of planets
• Surfaces and atmospheres of their satellites
  (Heavy ions of O and S. This does not occur for
  the Earth!)

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Astronomy 330

• Oxygen ions found around Jupiter and Saturn
• Some of these ions (also other neutral atoms)
  come from IOs volcanoes. Sputtering is another
  source (impacts of high energy ions with the
  satellites solid surface).
• The region around IO is so charged with particle
  radiation it would be lethal the humans and it is
  also hazardous to spacecraft. It almost killed
  Pioneer 10 and Galileo, even though it was
  designed for this, was almost useless at the end
  of it mission.

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• Saturn sputtering occurs as well from its icy
  satellites and from its ringssupplies Oxygen
  ions.
• Nitrogen ions come from the atmosphere of Titan.
• Three sinks for charged particles in belts
• Escape from outer magnetosphere.
• Collisions with upper atmosphere.
• Collisions with rings and inner satellites.
• Absorptions at Saturn are stronger (more dense
  ring system). This causes a major difference in
  magnetospheres of Jupiter and Saturn.

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Astronomy 330

• The magnetic fields of Jupiter and Saturn are
  much stronger than the Earths.
• Also the solar wind is weaker.
• This results in magnetospheres for each planet
  which are larger than the Sun!
• The upstream boundaries also fluctuate due to the
  changing solar wind.
• Titan is sometimes inside the magnetosphere of
  Saturn and sometimes outside it.

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Astronomy 330

• In the downstream direction, a magnetotail forms.
• Jupiters is so long that it reaches to the orbit
  of Saturn.

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Astronomy 330 Another view of Jupiters
Magnetosphere (from Cassini)
http//photojournal.jpl.nasa.gov/catalog/PIA03476
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Astronomy 330

• The rotation of the planets supplies the energy
  to power their magnetospheres since this is
  ultimately what generates their magnetic fields.
• The charged particles in the magnetosphere
  exhibit solid body rotationthey move with the
  planet as if they are attached to it.
• At IO, this speed is much faster than the orbital
  speed of IO and the plasma torus passes by IO a
  wake precedes the IO in its orbit. Also happens
  at Titan around Saturn.

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Astronomy 330

• As a result of all this energy generation in the
  magnetic fields, the rotation rates of Jupiter
  and Saturn are slowing (but only very slowly).

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Astronomy 330 Auroras

• Charged particles follow the magnetic field lines
  and impact the atmospheres of these planets near
  their polesas on Earth.
• This has been seen on Jupiter by direct
  photography and in the UV and IR.
• This also results in new compounds being produced
  as molecules of methane break apart.
• UV auroras are present on Saturn, but not strong
  IR emission.
• Visible auroras not detected on Saturn by
  Voyagersnight side is never really dark due to
  rings!

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Astronomy 330 Aurora on Jupiter showing
footprints of Galilean satellites
http//photojournal.jpl.nasa.gov/catalog/PIA03155
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Astronomy 330 Results from Cassini

• Went in orbit around Saturn in July, 2004.
• Has revealed a dynamic magnetosphere on Saturn.
  Its chemical environment resembles that around
  comets.
• Saturns winds change with altitude.
• Small storms merge to form larger ones.
• Observations indicate convection from the
  interior may maintain strong winds on Saturn
  (remember stronger than Jupiters).

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• Auroras detected, different than either Earths
  or Jupiters.
• Auroras last for days on Saturn, on Earth only
  hours.
• Suns magnetic field and Solar wind have a larger
  effect then previously thought

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Astronomy 330 Saturns auroras in UV
http//www.nasa.gov/mission_pages/cassini/media/ca
ssini-hubble-021605.html
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Astronomy 330 Reading

• Read about some of the results from
  Cassini-Huygens at
• http//www.nasa.gov/mission_pages/cassini/main/Cas
  sini_News_Collection_archive_1.html

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Astronomy 330