Download Jupiter and beyond

1B11
Foundations of Astronomy
The Jovian Planets
Silvia Zane, Liz Puchnarewicz
[email protected]
www.ucl.ac.uk/webct
www.mssl.ucl.ac.uk/
1B11 The Giant Planets
The 4 “giants”
PLANET
MASS
RADIUS
DENSITY
Jupiter
Saturn
Uranus
Neptune
317 M
95 M
14.5 M
17.1 M
11.3 R
9.4 R
4.0 R
3.9 R
1.3 g/cm3
0.7 g/cm3
1.2 g/cm3
1.7 g/cm3
INTERNAL
HEAT
yes
yes
?
yes
MOONS
RINGS
16 (4 "large")
18 (1 "large")
15
8 (1 "large")
yes
yes
yes
yes
+ the icy object Pluto
• Low densities  mostly H & He (ices for Uranus, Neptune)
• “Surfaces” : cloud tops
• Magnetic fields: all strong (Jupiter’s mag. Moment 20.000 Earth’s)
• Internal heat: J, S, N radiate  twice the heat they receive from the
Sun  internal heat e.g. gravitational contraction ( 1mm/year), etc..
1B11 The Interior
Ex. Jupiter
Based on mean density, assumed chemical composition.
And Hydrogen Phase diagram
T 165K
P 1 bar
T10000K
P3 Mbar
Liquid Molecular
H (+ He)
T20000K
P70 Mbar
Liquid Metallic H (+ He)
15%
(Radius)
75%
100%
? Rocky-ice core10-15 M
Clouds (complex molecules)
1B11 The Interior
Ex. Uranus and Neptune
H20 (+ He)
Ices (H20 , CH4)
30%
(Radius)
75%
100%
Rocky core?
Same size as rock/ice core of Jupiter and Saturn
1B11 The Interior
Hydrogen Phase diagram
T(K)
J
104
S
Liquid H2
U, N
Liquid Metallic
103
Solid H2
102
0.1
Solid Metallic
1.0
10
100
P (Mbar)
1B11 The Surface Layers
Predicted Cloud Structure
Altitude (km)
0.1 bar
1 bar
+50
NH3
0
NH4SH
-50
-100
H2O
120
160
340
10 bar
T(K)
• These clouds are white. The reds and brown observed clouds result
from more complex hydrocarbons produced by photolysis of NH3,
CH4, etc..
•Clouds are more muted on Saturn, owing to lower UV
1B11 The Surface Layers
This animation of Jupiter was
created from a mosaic of
images taken by the Voyager
spacecraft.
As the animation starts, the
great red spot is towards the
left side. A number of brown
spots can be seen just above
center.
1B11 Internal Heat
Jupiter, Saturn and Neptune all radiate about twice as much
energy as they receive from the Sun
 An internal heat source, possible responsible for dynamic
meteorology of Jupiter
Possibilities:
• Primordial heat
• Gravitational Contraction ( 1mm/yr)
• Combination of all of these…
1B11 Planetary rings
Moonlet, held
together by gravity
• All four giant planets have
rings
• Rings are composed of
small, solid (generally icy)
particles orbiting in equatorial
plane
Disrupted by
tidal forces
R
RP
• Probable origin: disruption
of small moons or comets
within a giant planet’s Roche
limit
1/ 3
 P 

R  2.4 RP 
  m
1B11 Major Satellites of Jupiter and Saturn
Jupiter (Galilean Satellites, 1610)
NAME
DIST
(106 KM)
RADIUS
(KM)
COMPOSITION
NOTES
1820
MEAN
DENSITY
(G CM -3)
3.5
Io
0.42
rock
0.67
1570
3.
Ganimede
1.07
2630
1.9
Rock with ice
crust
Rock/ice
Callisto
1.88
2400
1.8
Rock/ice
Highly
vulcanic
Possible
ocean
Heavily
cratered
Heavily
cratered
Europa
MEAN
DENSITY
(G CM -3)
1.9
COMPOSITION
NOTES
Rock/ice (?)
Thick N2
atmosphere
(clouds)
Saturn (Titan, 1655)
NAME
DIST
(106 KM)
RADIUS
(KM)
Titan
1.22
2575
1B11 Galilean Satellites: Summary
Io:
• Highly volcanic
• Energy Source: tidal friction
Europa:
• icy crust, few craters
• Evidence for ocean:
• recent resurfacing (new ice)
• surface features (ice flows)
• spectral evidence for salts
•  possible biosphere ?
1B11 Galilean Satellites: Summary
Ganimede, Callisto:
• Thick icy mantles to keep density low
Silicate mantle
Possible core ? (esp.
Ganimede)
Heavily cratered icy
crust (esp. Callisto)
Ice (possibly
liquid at depth)
• Both probably now inert, Ganymede has been
active more recently than Callisto (few craters 
younger surface)
1B11 Titan (moon of Saturn)
Atmospheric composition:
N2: 82 –99%
CH4: 1-6 %
Ar: 1-6%
 Many Hydrocarbon traces, e.g. Ethane (C2H6)
• Clouds: organic molecules produced by photolysis
• Surface: ice? Covered in hydrocarbons, possibly liquid?
1B11 Triton (moon of Neptune)
Composition:
Ice/rock?
Very thin (10–5 bar) N2 and CH4 atmosphere
• It has a retrograde orbit  CAPTURED?
• similar object to Pluto?
1B11 Pluto (discovered 1930)
• Mean orbital distance: 39.5 AU
• Eccentricity: 0.25
• Orbital inclination: 17.1º
• Radius : 1150 km (0.18 R : smaller than triton!)
• Mean density: 2.0 g cm–3 (rock/ice composition)
• Atmosphere: very thin (10–5 bar) N2 with CH4 (like Triton)
• Moon: Charon (radius=595 km, orbital period 6.4 d)
1B11 Trans-Neptunian objects (TNOs)
•Since 1992 200 icy objects with diameters 100 km have
been found beyond Neptune.
•More than 70000 are thought to exist between 30 and 50 AU.
•Pluto and Triton are probably just the largest and/or the
closest members of the TNO population.
•TNOs probably mark the inner edge of the KUIPER beltsource of short period comets
1B11 web sites
http://www.ex.ac.uk/Mirrors/nineplanets
http://www.solarviews.com/eng/
Images of planets, missions, moons, rings.. And links therein!