#### Transcript The Gas Giants The Gas Giants Together they account for 99.5% of our planetary system Jupiter Saturn Uranus Neptune Mass (MEarth) 317.8 95.2 14.4 17.2 Distance from Sun (AU) 5.20 9.54 19.2 30.1 Equatorial Radius (REarth) 11.2 9.46 3.98 3.81 Average.

```The Gas Giants
The Gas Giants
Together they account for 99.5% of our planetary system
Jupiter
Saturn
Uranus
Neptune
Mass (MEarth)
317.8
95.2
14.4
17.2
Distance from Sun (AU)
5.20
9.54
19.2
30.1
11.2
9.46
3.98
3.81
Average Density (kg/m3)
1330
710
1240
1670
Size-Mass Relationship
• As with terrestrials, composition can be guessed from mean
density. But the high compressibility of volatiles must be
accounted for
 Initially, as they accrete mass they grow in radius
 But at a mass of ~300 earth masses, further accretion causes the
Composition
• Jupiter and Saturn are
well matched by H+He
models
 Require some ice/rock
as well
• Uranus and Neptune are
much better represented
by an icy composition.
1
T=0 K models
T>0K
Recall: Moment of Inertia
• The moment of inertia is a measure of degree of concentration
 Related to the “inertia” (resistance) of a spinning body to external
torques
 Shows giant planets are centrally concentrated: cores?
Body
I/MR2
Sun
0.06
Mercury
0.33
Venus
0.33
Earth
0.33
Moon
0.393
Mars
0.366
Jupiter
0.254
Saturn
0.210
Uranus
0.23
Neptune
0.23
0.4 for a homogeneous sphere
I

  0.67 for a hollowshell
2
MR
 0 for a point mass

Shapes
• Rotation induces significant
flattening of compressible
material
Body
a/(a-b)
Rotation
Period (d)
Sun
10000
25.4
Earth
298
1.0
Jupiter
16
0.41
Saturn
10
0.426
Heat Balance
• The average temperature of Jupiter is 160 K. Is it in thermal
equilibrium? (Assume a visible albedo of 0.43, but a perfect
blackbody in the infrared).
• An infrared picture of Jupiter
Atmospheres
• Similar thermal structure
to terrestrial planets
• Temperature of Jupiter
and Saturn is never low
enough to form a methane
cloud deck – which
dominates Neptune and
Uranus
H at high temperatures and pressures
• Atmosphere of Jupiter and
Saturn is mostly “liquid” H2.
• At very high pressures, H atoms
dissociate from each other and
their electrons
 Forms a metallic liquid
 Good conductor
Maximum of Earth-based
laboratory experiments
STP
Interiors
• Jupiter and Saturn are dominated by an
atmosphere of fluid, metallic hydrogen
• Neptune and Uranus are dominated by an
icy mantle, probably as a fluid,
conducting ocean, surrounded by a H and
He atmosphere
Cloud patterns
• Surface features
are due to forms
and colourations of
the highest cloud
layers
Magnetospheres
• The giant planets have strong magnetic fields
 Likely due to the convective, metallic hydrogen interior
 Interact with solar wind (and atmosphere of Io) to produce
spectacular aurorae
Summary: The Gas Giants
Jupiter
Saturn
Uranus
Neptune
Mass (MEarth)
317.8
95.2
14.4
17.2
Core (MEarth)
~15?
~15?
~13?
~13?
%Mass of Core
≤5%
≤15%
≤90%
≤76%
I/MR2
0.254
0.210
0.23
0.23
Heat Out/In
2.5
2.3
~1.1
2.7
Wind Max (km/s)
~100
≥400
≤200
≤200
Prot (hrs)
9.8
10.6
17.2
16.1
Magnetic Field (vs Earth)
20,000
6000
50
25
Convection?
Y
Y
Y?
Y
Break
Jupiter
• This shows Voyager
1's approach during a
period of over 60
Jupiter days.
• Notice the difference
in speed and direction
of the various zones
of the atmosphere.
• The interaction of the
atmospheric clouds
and storms shows how
dynamic the Jovian
atmosphere is.
Cloud motions in Jupiter’s atmosphere
The Coriolis force diverts N-S motion into E-W motion, in distinct
zonal bands (5 in each hemisphere).
Infared and Optical
• Regions of white in visible light are dark in infrared
internal heat is blocked by the clouds
• Darkest visible bands are brightest in the infrared
seeing deeper into the atmosphere where it is hotter
• Red spot also dark in IR: cool, high altitude storm
Jupiter’s atmosphere
• Rising air from the deeper layers cools and forms clouds as it
rises; we see deeper where the high ammonia clouds have been
depleted by precipitation, much as on Earth rain will often mean
clearer skies.
Great Red Spot
•
•
Red colour probably from red phosphorous
A large eddy caused by rising hot gas and the Coriolis force
Oval BA
• A White oval storm, similar to the Red Spot but smaller
 Formed from colliding storms in 1998
• Recently turned Red
 May be bringing material to the upper atmosphere, where reactions with
UV solar rays change the colour.
Oval BA
• Near collision in July 2006
 Is now the size of Earth with winds reaching 645 km/s, similar to
the Great Red Spot
July 2006
Feb 2006
Saturn
Saturn… views never seen before
• From the Cassini spacecraft http://saturn.nasa.jpl.gov
Saturn… views never seen before
• From the Cassini spacecraft http://saturn.nasa.jpl.gov
• night side of Saturn is partly lit by light reflected from its own
ring system.
Earth
Faint E-ring,
created by
fountains
from
Earth from Saturn
Crossing the ring plane
Internal heating
•
amount as Jupiter does
 But Saturn is smaller, and this cannot all be gravitational energy
 It is thought that He forms droplets and sinks downward, releasing
gravitational energy
Thermal infrared
picture of Saturn
Storms on Saturn
• Like Jupiter, Saturn
shows large storms
• These are usually harder
to see, however
Storm at the pole
Uranus and Neptune
Uranus
• Bluish green colour, with far
fewer atmospheric features
than Jupiter and Saturn
Neptune
Colours of Uranus and Neptune
Uranus and Neptune: Interiors
• Likely have a rocky core, but are
dominated by a fluid, icy and ionic
ocean
• Surrounded by an atmosphere rich in
H and He
• Uranus is the only gas giant that does
not emit much more heat than it