Download 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 ?