1B11 Foundations of Astronomy

The Jovian Planets

Silvia Zane, Liz Puchnarewiczemp@mssl.ucl.ac.ukwww.ucl.ac.uk/webctwww.mssl.ucl.ac.uk/

1B11 The Giant Planets

PLANET MASS RADIUS DENSITY INTERNAL HEAT

MOONS RINGS

Jupiter 317 M 11.3 R 1.3 g/cm3 yes 16 (4 "large") yes Saturn 95 M 9.4 R 0.7 g/cm3 yes 18 (1 "large") yes Uranus 14.5 M 4.0 R 1.2 g/cm3 ? 15 yes Neptune 17.1 M 3.9 R 1.7 g/cm3 yes 8 (1 "large") 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..

The 4 “giants”

1B11 The Interior

Based on mean density, assumed chemical composition. And Hydrogen Phase diagram

Ex. Jupiter

Liquid Metallic H (+ He)

Liquid Molecular H (+ He)

? Rocky-ice core10-15 M

Clouds (complex molecules)

15% (Radius) 75% 100%

T20000KP70 Mbar

T10000KP3 Mbar

T 165KP 1 bar

1B11 The Interior

Ex. Uranus and Neptune

Ices (H20 , CH4)

H20 (+ He)

Rocky core?

Same size as rock/ice core of Jupiter and Saturn

30% (Radius) 75% 100%

1B11 The Interior

Hydrogen Phase diagram

P (Mbar)

T(K)

Liquid H2

Solid H2

Liquid Metallic

Solid Metallic

104

103

102

0.1 1.0 10 100

JS

U, N

1B11 The Surface Layers

Predicted Cloud StructureAltitude (km)

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

-100-50

0

+50 0.1 bar1 bar

10 bar

120 160 340

NH3

NH4SH

H2O

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

• All four giant planets have rings

• Rings are composed of small, solid (generally icy) particles orbiting in equatorial plane

• Probable origin: disruption of small moons or comets within a giant planet’s Roche limit

RP

R

Moonlet, held together by gravity

Disrupted by tidal forces

3/1

4.2

m

PPRR

1B11 Major Satellites of Jupiter and Saturn

NAME DIST (106 KM)

RADIUS (KM)

MEAN DENSITY (G CM -3)

COMPOSITION NOTES

Io 0.42 1820 3.5 rock Highly vulcanic

Europa 0.67 1570 3. Rock with ice crust

Possible ocean

Ganimede 1.07 2630 1.9 Rock/ice Heavily cratered

Callisto 1.88 2400 1.8 Rock/ice Heavily cratered

NAME DIST (106 KM)

RADIUS (KM)

MEAN DENSITY (G CM -3)

COMPOSITION NOTES

Titan 1.22 2575 1.9 Rock/ice (?) Thick N2

atmosphere (clouds)

Jupiter (Galilean Satellites, 1610)

Saturn (Titan, 1655)

1B11 Galilean Satellites: Summary

• Highly volcanic• Energy Source: tidal friction

• icy crust, few craters • Evidence for ocean:

Io:

Europa:

• recent resurfacing (new ice)• surface features (ice flows)• spectral evidence for salts• possible biosphere ?

1B11 Galilean Satellites: Summary

• Thick icy mantles to keep density low

Ganimede, Callisto:

• Both probably now inert, Ganymede has been active more recently than Callisto (few craters younger surface)

Heavily cratered icy crust (esp. Callisto)

Ice (possibly liquid at depth)Possible core ? (esp.

Ganimede)

Silicate mantle

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 belt-source 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!