JUPITER: King of the Planets
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Transcript JUPITER: King of the Planets
JOVIAN (GAS GIANT) PLANETS
SATURN
Nearly as big as
Jupiter, and it
rings very nicely.
Cassini image of
Saturn,
edge-on
rings, their shadows,
& moons Dione &
Enceladus
SATURN: Ringed and Very Gassy
• Mass is 95.2 times that of Earth.
• Radius is 60,268 km or 9.45 times Earth's.
Density is only 0.687 g/cm3 or 0.125 of Earth's.
• The most distant naked eye planet.
• Period of 29.42 years.
Semi-major axis, a = 9.54 AU,
e = 0.054.
Inclination to ecliptic = 2.49 deg
• 9 moons discovered from the ground.
• No solid surface: differential rotation
Magnetic (interior) spin period: 10h 40m
Spins so fast & is so gassy that its ellipticity > 10%
axial tilt = 26.7 deg
Rings and Orbit
Rings are
prominent; tilted
at 27 degrees
so seen from
different angles
from Earth;
nearly invisible
when edge-on
Saturn's Atmosphere and Interior are
Very Similar to Jupiter's
BUT the main interior differences include:
• Lower density: less mass so less
compression and relatively more gaseous
• Molecular H2 layer 30,000 km thick
Metallic H layer 15,000 km thick
Rocky/metallic core, R 15,000 km
• Central: T = 15,000 K; P = 5 x 106 atm
• Strong magnetic field, but still only ~5% of
Jupiter's.
Saturn’s Interior
Saturn’s Atmospheric Differences from
Jupiter
• Fewer belts and zones (due to lower T)
but
faster winds (to 1500 km/h)
Thicker cloud layers (lower gravity)
Less coloration (probably due to lower T)
• In atm: H2 over 92%, He almost 8%; Why?
• He has settled or “rained” downwards.
At the lower T and P of Saturn's atm,
He doesn't dissolve in H2
Separation of He and compression of whole
planet yields much more heat, so Saturn's surface T
is 97 K, not 74 K.
Saturn’s Atmosphere
• Real color from
HST showing storm
near equator and
pole at earlier time.
• False color image
from IR:
blue, haze free;
green, more haze;
orange, high clouds
Atmospheric
Structure and Fast
Winds
URANUS and NEPTUNE
Most Distant Official Planets are NEARLY TWINS
• MU = 14.54 M ; MN = 17.15 M .
• RU = 25,559 km or 4.01 times Earth's.
• RN = 24,766 km or 3.88 times Earth's.
• U = 1.27 g cm-3 ; N = 1.64 g cm-3 .
As seen from Earth, URANUS
• Discovered by Wm. Herschel
in 1781 (barely visible to
naked eye, greenish, nearly
featureless)
• Period of 83.75 years
• Semi-major axis: 19.19 AU, e
= 0.047
• 5 moons discovered from the
ground pre-space; 10 by
Voyager, 2 more by 200-inch.
• Tilted by 98 deg LONG
seasons
• Magnetic (interior) spin
period: 17.2 h (retrograde)
Seasons on Uranus
• Axis almost in orbital plane so equatorial zones have two summers
near equinoxes and two winters near solstices: poles have 42 yr of
light and 42 years of dark
Rotation on Uranus
• HST shows
cloud
motions
over 8 hours
• IR HST
picture
shows
clouds and
rings
As seen from Earth, NEPTUNE
• Predicted by John Adams
(1845) and Urbain Leverrier
(1846): producing growing
error in Uranus's position
noticed over the years
• Found in the right place by
Johann Galle in Sept. 1846 -bluish, tiny disk; Voyager
showed some bands
• P=163.7 yr; a = 30.07 AU;
e=0.009
• 2 moons discovered from the
ground; 11 from space
• Magnetic (interior) spin
period: 16.1 h; surface 17.3 h
ATMOSPHERES
• Temperatures: Uranus, 58 K; Neptune 59 K
• Both Uranus and Neptune are about 84% H2 and 14% He.
• Methane (CH4 ) is most of the remainder
Methane absorbs red light, so planet looks blueish/green
More CH4 in Neptune, so it's bluer
Ammonia is frozen out in these very cold atmospheres
• No internal heat source for Uranus, so washed out bands
and zones covered by a haze.
Fairly strong winds
distribute Sun's heat so sunny side isn't much hotter than
shady side.
• Neptune has an internal heat source: probably extra
methane has helped to trap internal heat of formation
more noticeable bands and some storms
Neptune’s
Dark Spot
(from
Voyager) and
Clouds
from IR HST
views
showing
brightening as
more sunlight
hits South
side
Interiors of Uranus and Neptune
• Below atmospheres, each about 1/3 of R:
• MOLECULAR HYDROGEN (unlikely to convert to
metal)
• below that, SLUSH, including water ice and dissolved
ammonia: an electrically conducting fluid
• ROCKY CORE (maybe 10 M )
Magnetic
Fields
• Despite not having (much) metallic hydrogen both have
substantial internal fields (100 times earth's, 1/10th
Saturn)
• Off-center and misaligned with spin axis (60O for Uranus,
46O for Neptune, vs. 10O for Jupiter and well-aligned for
Saturn).
• Why?: currently reversing; reflecting a blow; ionic NH3 ?