ASTRONOMY 161 Introduction to Solar System Astronomy

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ASTRONOMY 161Introduction to Solar System
Astronomy
Class 20
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Jupiter Saturn Friday, November 13
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Jupiter Basic characteristics

• Mass 1.8991027 kg (317.8 Earths)
• Diameter 142,984 km (11.21 Earths)
• Density 1,326 kg/m³
• Sidereal rotation period 0.413 d (9 h 55 min)
• Albedo 0.52 (Earth 0.39)
• Average distance from Sun 5.203 A.U.

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Saturn Basic characteristics

• Mass 5.6851026 kg (92.16 Earths)
• Diameter 120,536 km (9.45 Earths)
• Density 687 kg/m³
• Sidereal rotation period 0.449 d (10 h 47 min)
• Albedo 0.47 (Earth 0.39)
• Average distance from Sun 9.537 A.U.

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318 MEarth 11.2 REarth
95.2 MEarth 9.44 REarth
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Spacecraft Visits to Jupiter

• Fly-bys
• Pioneer 10 11 (1973/74)
• Voyager 1 2 (1979)
• Ulysses (1992)
• Cassini (2001)
• Orbiters
• Galileo (arrived Dec 1995, crashed into Jupiter
  in 2003)
• Dropped an atmospheric probe in Dec 1995

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Spacecraft Visits to Saturn

• Fly-bys
• Pioneer 11 (Sept 1979)
• Voyager 1 (Nov 1980)
• Voyager 2 (Aug 1981)
• Cassini Orbiter
• Launched Oct 1997
• Arrived July 2004
• Huygens Titan probe,landed January 2005

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Jupiter and Saturn Key Concepts

• (1) Jupiter and Saturn consist mainly of hydrogen
  and helium.
• (2) Jupiter and Saturn have belts and zones of
  clouds, plus circular storms.
• (3) Jupiter and Saturn have magnetic fields
  created in metallic hydrogen.
• (4) Differences between Jupiter and Saturn are
  due to Jupiters higher mass.
• (5) All Jovian planets have rings.

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• Jupiter and Saturn are large planets.
• Radius of Jupiter 11 x radius of Earth
• Radius of Saturn 9 x radius of Earth.

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• Jupiter Revolution and Rotation
• Orbital period 12 years
• Rotation period 10 hours
• Jupiter is oblate (flattened at the poles), due
  to its rapid rotation.
• Its equatorial diameter is 6.5 greater than its
  polar diameter.

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• Saturn Revolution and Rotation
• Orbital period 29 years
• Rotation period 10 1/2 hours
• Saturn is extremely oblate.
• Its equatorial diameter is 10 greater than its
  polar diameter.

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(1) Jupiter and Saturn consist
mainly of hydrogen and helium.

• Jupiter
  Escape speed 60
  km/sec Air
  temperature 165 K (-160o F)
• Saturn
  Escape speed 35
  km/sec Air
  temperature 93 K (-290o F)
• Earth
  Escape speed 11 km/sec
  Air
  temperature 290 K (60o F)

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• Atmospheres of Jupiter and Saturn retain H, He.
• Because Jupiter and Saturn are cold and have high
  escape speed, they hang onto hydrogen and helium.
• Jupiters atmosphere is 75 hydrogen, 24 helium.
• Saturns atmosphere is 92 hydrogen, 6 helium.
• Question Where is Saturns helium?
• Answer Saturn is so cold, its helium condenses
  and rains downward.

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• Jupiter and Saturn radiate away more energy than
  they receive from the Sun.
• What is the source of the extra energy?
• Mostly, it is heat left over from when the
  planets formed. (Big objects cool more slowly).
• In addition, the helium rain of Saturn
  generates heat as it falls.

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• As objects fall, gravitational potential energy
  is converted to other forms of energy.
• Water at the base of Niagara Falls is 0.13o C
  warmer than at the top.

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(2) Jupiter and Saturn have belts and
zones of clouds, plus circular storms.

• Air heated from above by the Sun, from below by
  internal heat
• Strong winds and large storms.
• We see clouds of ammonia (NH3), colored by
  complex compounds.

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• Jupiters atmosphere is divided into
  light-colored zones and dark-colored belts.
• High-speed winds blow eats or west at the
  boundaries between them.

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Belts Zones of Jupiter

• Belts high pressure, high temperature
• Gaps in high clouds, view lower atmosphere
• Colors due to complex organics polysulfides
• Zones low pressure, low temperature
• Regions of cold, high ice clouds

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Atmosphere of Saturn

• The atmosphere is dividedinto dark bands
  bright zones likeJupiter's, but...
• Saturn is farther from the Sun, and colder.
• Makes the bands less chemically complex, and so
  more subtle less colorful than Jupiters.
• West-to-East winds are very strong
• 1800 km/hr, faster than on any other planet.
• Fewer and shorter-lived cyclonic storms.
• Occasional very powerful storms are seen.

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• Saturn has a similar pattern of zones and belts.
• They are less dramatic than Jupiters Saturns
  clouds are buried deep in its atmosphere and are
  blurred by haze.

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• The Great Red Spot of Jupiter
• An enormous circular storm (up to 40,000 km
  across) in the southern hemisphere of Jupiter.

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Great Red Spot
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• Great Red Spot high pressure system.
• Air flows outward, is deflected to the left by
  the Coriolis effect, and rotates
  counterclockwise.
• Great Red Spot was first seen in 1664!

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• News from Cassini!
• Saturn's Surprisingly Stormy South

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• Clouds are usually made of different stuff
  from the air they float in.
• Venus carbon dioxide atmosphere, sulfuric acid
  clouds.
• Earth nitrogen atmosphere, water clouds.
• Mars carbon dioxide atmosphere, water carbon
  dioxide clouds.
• Jupiter Saturn hydrogen atmosphere, ammonia
  clouds.

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(3) Jupiter and Saturn have magnetic fields
created in metallic hydrogen.

• The layers of Jupiter and Saturn (from the
  outside in)
• Ordinary molecular hydrogen (and helium)
• Liquid metallic hydrogen (and helium)
• Liquid water, methane, ammonia
• Solid rock core

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• Jupiter and Saturn are differentiated.

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Jupiter
Molecular Hydrogen
Metallic Hydrogen
Rock Ice
10-15 MEarth
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Saturn
Molecular Hydrogen
Metallic Hydrogen
Rock Ice
10-12 MEarth
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• Metallic hydrogen what is that?
• Metals shiny, malleable, conductors of
  electricity.
• Metals contain free electrons, not bound to
  individual nuclei.
• Hydrogen becomes a metal
  only at very high pressure
  (1.4 million
  atmospheres).
• Just like the Earth, Jupiter
  and Saturn have a layer
  of
  liquid metal.

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• A magnetic field is generated by the circulation
  of liquid metal.
• Jupiter has very rapid rotation, lots of liquid
  metallic hydrogen Jupiter has a very strong
  magnetic field, which has trapped charged
  particles.

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(4) The differences between Jupiter and Saturn
are due mainly to Jupiters larger mass.

• Compared to Jupiter, Saturn
• Is lower in density,
• Is more flattened,
• Has less metallic hydrogen,
• Has smaller magnetic field.
• All these are due to the fact that Saturn is
  lower in mass Saturn 95 Earths, Jupiter 318
  Earths.

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(5) All Jovian planets have rings.

• Only rings of Saturn are broad and bright.
• The (gradual) discovery of Saturns rings
• 1610 Galileo looks at Saturn,
  notices it is not circular.
• 1655 With a better telescope,
  Huygens discovers ring.

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• 1675 With a better telescope, Cassini discovers
  gap in the ring.
• 1980 Voyager 1 spacecraft finds the rings are
  made of innumerable ringlets.

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• 1977 Rings of Uranus discovered during a stellar
  occultation (the eclipse of a distant star by
  Uranus).

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• 1979 Rings of Jupiter discovered by the Voyager
  1 spacecraft
• The rings are faint, and are made of tiny dust
  particles.

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• 1985 Rings of Neptune discovered during a
  stellar occultation.
• Image obtained by the Voyager 2 spacecraft in
  1989.

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• What are rings made of?
• Rings are not monolithic they consist of many
  moonlets, each orbiting the central planet.
• Size of moonlets is found by radio occultation.
  (A wavelength smaller than moonlet is blocked.)
• Composition of moonlets is found from the
  spectrum of reflected light.

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• Saturns rings are made of ice particles from 1
  centimeter to 5 meters across. (Most are a few
  inches across.)
• Jupiter dark dust particles.
• Uranus dark chunks a meter across.
• Neptune dark chunks range of size.

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• Saturns rings are very thin!!
• Rings are 270,000,000 meters in diameter.
• Rings are only 30 meters thick.
• When the rings are edge-on, they are nearly
  invisible.

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• The ice in Saturns rings would make a moon about
  100 km across. Where had all that ice come from?
• Leading hypothesis the rings were originally a
  moon that was pulled apart by Saturns tides.
• Tidal force exerted by a planet on a moon tend to
  stretch it apart.

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• The moons own gravity tends to hold it together.
  
• As the moon approaches the planet, tidal force
  increases.
• At what distance will the moon be ripped apart?
• Roche limit distance at
  which tidal force pulling
  moon apart
  equals
  self-gravity holding moon
  together.
• Roche limit
  2.4 x planet
  radius

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• Lots of other interesting phenomena
• Saturns rings have many gaps orbital resonance
  with moons.
• Narrow rings are kept from spreading by shepherd
  moons.

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• News from Cassini!
• The Hand of Prometheus

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Few closing questions

• 1) Name the major differences and similarities
  between Jupiter and the Earth.
• 2) Name the major differences between Jupiter and
  Saturn.
• 3) Is there magnetic field around Saturn?
• 4) Are there volcanoes on Jupiter?
• 5) Are there quakes on Saturn?
• 6) Could Mars have a ring?