Transcript L8 – Jan 31/08

SCI238 W08
Lecture 8: Jovian (Giant)
Planets
Neptune and Triton
image from Voyager 2
spacecraft (1989)
L8 – Jan 31/08
Jovian Planets
This week’s events:
the Moon: New Moon Feb 7
Venus: visible low in east before sunrise; brightest
“morning” star
Mars: is visible all night, rises at sunset
Jupiter: passing Venus. take a look at 6am 1 -3 Feb!
Saturn: rises at 8pm
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Jovian Planets
Today’s Lecture
 announcements etc…
 assignment 2, also posted on course webpage
 Moon
 terrestrial planets compared
 overview of the Giant Planets
 interiors
 “surface” features
 atmospheres
 magnetic structures
 moons
 rings
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Jovian Planets
Moon’s interior
differentiated, but
not as “extreme”
differences as Earth
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Jovian Planets
Craters on the Moon are due to impact events
Impact craters found throughout SS
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Jovian Planets
Impact process forms characteristic shape...
impact
ejecta
circular, rimmed, low floor
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Jovian Planets
Maria and Highlands are different in age
How do we know?
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Jovian Planets
Apollo astronauts returned samples from many locations
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Jovian Planets
Lunar samples: radioactive dating => relation
between surface density of craters and age
60,000
# Craters (>1km)
age of oldest
samples: ~4.4x109
yr (highlands)
40,000
maria samples: ~3x109yr
youngest lunar surface
samples ~109yr
4
2
0
Age of Surface Deposit (Gyr)
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Jovian Planets
Terrestrial surfaces have different “ages”
What is the pattern
(correlation) here?
Crustal rock solidified globally
L8 – Jan 31/08 first on Moon, last on Earth
Jovian Planets
Comparative Planetology…
 interiors – role of mass
 atmospheres – role of mass,
distance from sun
 surfaces – liquid water, lava,
tectonics, impacts, surface age
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Jovian Planets
All terrestrial bodies are differentiated
=> All had hot (and fluid) interiors at some time
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Jovian Planets
Larger terrestrial planets:
•cooled more slowly
•more and longer lasting tectonic activity
•easier to retain atmosphere
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Jovian Planets
For planets closer to the sun:
•higher T
•harder to retain liquid water, atmospheres
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Jovian Planets
higher rotation => more “weather”
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Jovian Planets
fewer impact craters on massive planets:
• cooled more slowly
• atmospheres shield only against small impactors
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Jovian Planets
 Giant Planets
size
interiors
atmospheres, rapid rotation, circulation
magnetic fields
satellites
rings
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Jovian Planets
Physical Properties of the Jovian Planets
(mostly Earth units)
Planet
radius
mass
Density
(kg/m3)
Prot (d)
axis
tilt
Mag.
field?
gsurf
Earth
6,378km
5.97×1024
kg
5,520
0.9973
23.45
Y
9.8m/s2
Jupiter
11.2
317.9
0.24
0.41
3.08
Y
2.36
Saturn
9.5
95.2
0.12
0.44
26.73
Y
0.92
Uranus
4.0
14.5
0.23
-0.72
97.92
Y
0.91
Neptune
3.8
17.1
0.30
0.67
29.6
y
1.14
Jovian planets: size comparison
Jupiter by far the largest
all >> Earth
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Uranus, Neptune similar
Jovian Planets
the giant planets are rapidly rotating, large
“gravitationally bound” balls of fluid.
although gravity tends to pull fluid together into a
sphere, rotation flattens this into an “ellipsoid”.
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Jovian Planets
Saturn is the most oblate giant planet
Rpolar = 0.9 Requatorial
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Jovian Planets
Jupiter’s interior is differentiated
mostly metallic H!
core: rocky+metallic
+H compounds
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Jovian Planets
Jovian planets: all have differentiated interiors
Cores all ~10-15MEarth
J,S: higher % H, H compounds
U,N: higher % rocky, H mostly in methane, ammonia
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The Structure of Jupiter’s Atmosphere
as with terrestrial atmospheres: clouds, T, altitude
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Jovian Planets
atmospheres ~same structure…
differences: Tmax, pressure, some composition
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Jovian Planets
Bands in Jupiter’s atmosphere:
result of heat, convection, rotation (Coriolis)
visible light image
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IR image
Jovian Planets
the colour
differences between
various components of
Jupiter’s atmosphere
combined with the
circulation pattern
produce distinctive
banding structure.
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Jovian Planets
Jupiter’s Great Red Spot is a high pressure storm
region
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Jovian Planets
…and the white spot is a low pressure storm region
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…and now Jupiter has a second large red storm
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Saturn too has bands and storms, but less prominent
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Jovian Planets
Neptune and Uranus’ blue colour:
methane absorbs red λ and reflects blue
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Jovian Planets
all 4 jovian planets have strong magnetic
fields and huge magnetospheres
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Uranus’ and Neptune’s magnetic fields
Jovian Planets
strongly tilted re rotation axis
we also see auroral zones near the magnetic poles
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Jovian Planets
3/4 Jovian planets have internal heat sources
planet
TBB(obs)
“total”
Power
Internal
Power
Jupiter
127K
2x input
4x1017 W
Saturn
97
2.8x
2x1017
Uranus
58
~1x
1015
Neptune
56
2.5x
3x1015
Primordial heat? Helium rain?
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Other?
Jovian Planets
Jupiter: strongest,
most colourful
bands, storms…
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Jovian Planets
Jupiter
 very layered atmosphere
 hydrogen/helium, methane, ammonia, water
 strong “banding” – seeing different cloud layers
 white at depth “0 km” is ammonia
 red at depth 25 km is ammonia hydrosulphide
 blue at depth 100 km is water ice
 Giant Red Spot – a giant storm seen since first
telescope viewed Jupiter, fading a bit perhaps, but
still 40,000 km wide; and now another!




strong magnetic field
no true surface
very oblate planet (fast rotation)
hotter than expected – but not Greenhouse effect
 planet is contracting!
 mostly H/He interior with metallic H and rocky core
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Jovian Planets
Saturn: prominent ring system, more subtle
bands
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Jovian Planets
Saturn
 similar to Jupiter but smaller
layered banded atmosphere
hydrogen/helium, methane, ammonia
strong magnetic field
metallic hydrogen and rocky core
rings are most massive and prominent of all
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Jovian Planets
Cassini-Huygens mission to Saturn
 a joint NASA-ESA mission to
explore Saturn and its moons
 web site at saturn.jpl.nasa.gov
 reached Saturn 30 June, 2004
(after seven year flight)
 now in 4 year mission, orbiting
through the Saturn system
 recent results: in the midst of
series of flybys of Titan (last on
15 Jan. 2006)
 Huygens
 probe toTitan Jan 24/2005
 landed in mud
 has found water ice, methane
springs, rivers with islands
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Epimetheus (30 Mar. 2005)
Jovian Planets
Uranus: almost completely featureless in
visible light
but shows more detail in IR
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Jovian Planets
Uranus
 accidentally discovered telescopically in 1781
 faint features, blue atmosphere
 hydrogen, helium, methane, BUT NO
AMMONIA
 strong magnetic field
 hydrogen NOT metallic, rocky core
 rotation axis tilted 98o → very strong
seasonal effect
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Jovian Planets
Neptune shows large
storm features, like
Jupiter
the storms change
over timescales of
years or less
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Jovian Planets
Neptune
 position predicted from observations of
Uranus
 discovered in 1846
 very similar to Uranus, but more methane
 more cloud features
 warmer(!) than Uranus
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Jovian Planets
Jovian satellites:
some large, many small
some have been
geologically active:
now or in the past
some formed
with planet,
some captured
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Jovian Planets
Jupiter’s Large Satellites
 Io
 geologically active (with active volcanoes!)
 covered in orange sulphur compounds
 strongly tied to Jupiter’s magnetic field
 Europa
 smooth surface with few craters
 water ice, possibly over liquid water
 Ganymede
 largest moon in the Solar System
 water ice over much of surface
 Callisto
 heavily cratered
 concentric circular ridges are signs of a large impact
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Jovian Planets
the four “Galilean” satellites of Jupiter
Io
Europa
Ganymede
Callisto
surface “age” ↑ and mean density ↓
with distance from Jupiter
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Jovian Planets
Io: most volcanically active body in SS
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Jovian Planets
Io: volcanoes are frequent
…constantly changing surface appearance
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Jovian Planets
Io: tidal
interaction
and eccentric
orbit heat its
interior
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Jovian Planets
Io, Europa,
Ganymede:
and orbital
resonance
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Jovian Planets
Charged particles escaping Io interact with
Jupiter’s magnetosphere => Io torus
Periodic variability in
radio emission from
torus first observed
in 1960s
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Jovian Planets
Europa’s smooth surface and cracked terrain
the result of tidal heating and icy composition
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just below Europa’s surface: liquid
water or warm convecting ice?
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Jovian Planets
Ganymede’s
surface shows
both old and
young regions
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Jovian Planets
Callisto’s
surface is the
“oldest” of the
four Galilean
satellites
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Jovian Planets
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Jovian Planets
Saturn’s Moons
 many moons, but probably a large number
still to be discovered
 Titan: largest of Saturn’s moon’s – has a
thick atmosphere, extending far out into
space, probably has frozen water (ice)
 innermost moons tidally locked to planet
 moons interact with rings
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Jovian Planets
Titan: Saturn’s largest moon; has a thick atmosphere
methane,
nitrogen…
smoggy
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Jovian Planets
Huygens probe shows some
surface features on Titan
Titan: icy “rocks”, “river” valleys…
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Jovian Planets
Saturn’s Moons are varied, enigmatic
deathstar Mimas
old Dione
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icy Enceladus
streaky Rhea
cratered Tethys
two-faced Iapetus
Jovian Planets
Uranus’ moons
 more than 20 small ones, some irregular in
shape, some retrograde
 five midsized: Miranda, Ariel, Umbriel,
Titania, Oberon
 All icy, varied geological history
 Miranda is strange – very fractured surface,
some cataclysmic event?
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Jovian Planets
near IR image
shows Neptune’s
rings and seven
of its moons
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Jovian Planets
Urabus’ Miranda shows a fractured surface,
obvious violence, but from what?
messed-up
Miranda
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Jovian Planets
Neptune’s moons
 five small inner moons near ring system
 two larger, icy…
 five small outer, retrograde
 Triton
• very much larger than any other Neptune moon
• has thin nitrogen atmosphere
• surface has nitrogen geysers
• retrograde (backwards) orbit
• spiraling in towards Neptune
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Jovian Planets
Triton: moon of Neptune
Nitrogen
atmosphere
surface has been
reshaped by
geological activity
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Jovian Planets
Saturn’s Rings: the brightest, best known
 within “Roche Limit” of Saturn where any large
rocks (moons) break up due to tidal effects
 major rings (“A”, “B”, and “C”) with gaps between
them “Cassini’s Division”
 composed of icy particles with sizes between 1
micron and 10 meters
 Voyager discoveries:
 several other rings
 fine rings within each ring, like record grooves:
“spiral density waves”
 short-lived spokes
 braided rings
 “shepherd” satellites
 rings are very thin – at most a few tens of meters
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Jovian Planets
Saturn’s rings are wide, thin,
and complex
Radio image
colours ->
particle size
purple: mainly >5cm
green: mainly <1cm
white: particle
density too high
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Jovian Planets
Shepherd moons control the width of rings…
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Jovian Planets
…and also
make gaps
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Jovian Planets
“spokes” in Saturn’s rings: charged particles
briefly suspended above the plane?
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Jovian Planets
Galileo spacecraft shows rings around Jupiter
ring particles are small and dark: debris from Metis..
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Jovian Planets
Near IR image shows rings around
Uranus and some of its moons
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Jovian Planets
Neptune’s rings are narrow and
bright with dusty regions
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Jovian Planets