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Lecture 17

key points (lecture 17, 18 and 19)


Department
Astronomy
Course Code
ASTA01H3
Professor
Rick Halpern
Lecture
17

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Lecture 17: Saturn
oRings go through phases
oDensity less than water
o1/3 mass of Jupiter
oRotation speed squashes the Saturn so that equatorial diameter is
10% bigger
oAtmosphere
oZones and band structures less colouration than Jupiter
oCloud layer thicker than Jupiter
oConsists of molecular hydrogen, helium, methane and
ammonia
oExperiences a rain of helium from upper clouds
oSimilar to jupiters atmosphere but less pressure
oWind pattern same as Jupiter with zonal flow
oInterior Structure
oMolecular hydrogen, Metallic hydrogen and icy rocky core
oBottom of molecular hydrogen layer is hotter than Suns’
photosphere
oSaturn radiates 3 times more energy than it gets because its
cooling off
oHelium and hydrogen not mixed well, helium condenses into
droplets and falls back
oGravitational field compresses helium and heats it up
oMagnetosphere
oSaturn has a strong magnet field but only 5% of jupiters,
creates aurorae
oRings
o250 000km diameter and 1 km thick
oRing system from closest to Saturn
1.C Ring
2.B Ring
3.Cassini Division
4.A Ring
5.Encke Gap
oRing crossing occur every 15 years
oRing phases occur due to the tilt of rings relative to orbital
plane
oFormation of rings unknown probably from catastrophic
event
oParticles range from few millimeters to tens of meters
oComposition: water, ice
oRings cannot form into a moon because of tidal forces would
tear it apart
oRings lie within the Roche limit (closest distance that moon
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would survive)
oRoche limit is close to 2.5 planet radii
oRings emit radiation of varying intensities in EM spectrum
depending on radius
oRadial spikes are found on the rings
oCassini division is not completely empty
oResonance caused by effect of moon mimas 2:1 resonance
oMimas pulls on objects at the same location at every other
orbit
oThe net effect is the object is removed from that location
Lecture 18: Uranus
oalmost feature less
oDiscovered 1781 by Herschel, first planet to be discovered in 2000
years
oSemi-major axis 19.19 AU Period is 83.75 years
o27 small moons and 5 medium size moon
oPecularity of Uranus
oAxis of rotation lies in the plane of orbit
oSeasonal variations are extreme
oSeasons last about 21 years
oOuter atmosphere same as Jupiter
oAmmonia freezes, methane dominates and gives the blue colour
oSame temperature as Neptune 59K
oNo internal heat source
oRotation rate is 15 hours
oHas Rings
oUranus and Neptune have magnetosphere
oBar magnet is off of center
oMiranda moon jigsaw moon
Neptune
oNeptunian spots
oDiscovered in 1846 after analysis of Uranus orbit
oNeptune semimajor axis is at 30.07 A.U period is 163.7 years
o2 Moons called Nereid and Triton and 13 other moons
oNeptune has same temperature as Uranus indicating some sort of
internal heat origin unknown
o59K
oHas 5 rings, 3 narrow 1 wide
oNeptune has 13 moons only 2 seen from earth Triton and Nereid
oTriton is in a retrograde orbit
Triton surface has few craters indicating active surface
Triton was probably captured by Neptune
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