Jupiter

Largest planet by far.
Mass ∼ 318 (mass of earth) = 1.9 × 1027 kg ∼ 1/1000 mass of sun.
Orbital period = 11.89 years
ρ ∼ 1330 kg m-3
Radius ∼ 71398 km (equatorial), 68700 km (polar)

Rotational period 9 hrs. 50 mins (but note that it does not rotate as a solid body: 9 hrs 55 mins at poles)

Strongly banded appearance, corresponding to convective regions in atmosphere. Dark areas (bands) lie lower in atmosphere than light areas (zones).

Colours probably due to complex organic molecules: detected so far are:
  1. CH4 (methane),
  2. NH3 (ammonia),
  3. H2 (molecular hydrogen),
  4. C2H2 (acetylene),
  5. C2H5, PH3, H2O, G2H4 (germane), CO, HCN, H2S,

Clouds form at height corresponding to boiling point: top layer mainly ammonia.


Great Red Spot

: noted since 1600's
∼ 20,000 km × 50,000 km.

Speeds of rotation ∼ 500 km/hr
Now clearly seen to be "hurricane" (lifetime not too surprising: 1000 × bigger than terrestial hurricanes, so lifetime could well be 1000 × longer!)

Cassini At Jupiter: Red Spot Movie Credit: CICLOPS, NASA, JPL, University of Arizona

Top of spot extends well above surrounding cloud tops. Note downstream eddies. Colour probably from organic molecules stirred up from below.

RADIO SIGNALS Come from planet (presumably from thunderstorms) and from magnetosphere.

Structure of Jupiter is mostly hydrogen and helium (like a failed star!). Not all planets are solid enough to have craters: here is the results of Comet Shoemaker-Levy hitting Jupiter

MAGNETIC FIELD large: 4 gauss = 4 × 10-4 T (Not 4 × 10⁴, as in ZGS!)
Traps particles from solar wind giving very bright aurora (seen from Voyager)

RADIO SIGNALS Come from planet (presumably from thunderstorms) and from magnetosphere.

Structure of Jupiter is consistent with 75% H, 24% He and 1% metals, which is standard universe composition.

More heat radiated than recieved. Implies Jupiter nearly a star: rate of energy production ∼ 4 × 1017 W

Comes from continuing gravitational contraction: see later when we discuss stellar models.

MOONS OF JUPITER:

Jupiter has some of the oddest moons in the solar system. Four large easily visible with binoculars

Io

rotates
and is in a state of continuous volcanic eruption: Volcanoes:Plumes to 250 km
Vulcanism caused by "tidal pumping" by other moons.

Note surface is very unstable: no craters (age ∼ 106 yrs)

Surface of sulphur (hence yellow colour).
Io is surrounded by ionised sulphur and sodium cloud, modulating radio emission by Jupiter (since it is well inside magnetosphere)

Europa:

Rock covered with ice, probably slushy since no impact craters.

Large cracks, but no depth. Dark spots probably crustal rock.

Ganymede


Largest moon in the solar system: Ice on rock. Many craters, but with central pits, not peaks. Huge transverse faults

Callisto

Only Callisto seems to be more or less like a normal moon: The most cratered, ie not melted.

Very large impact crater (Valhalla) surronded by many rings.

At least 12 other moons (Amalthea) small, similar to Phobos and Deimos (i.e. like asteroids).

RINGS: smaller than Saturn's.


Saturn

Orbit period 29 yrs
Orbital Radius 1.4 × 109 km.
Planet Radius 53000-60000 km.
Density 680 kg m-3
Rotational period 10 hr 14 mins.

ATMOSPHERE similar to Jupiter, but less heating (internal & sun) so weather better


RINGS:

First seen by Galileo as "Handles"

Assumed to be solid, but Maxwell showed that tidal forces would have destroyed them...

Spectrum consistent with small ice pellets and dust (moonlets).Voyager showed

  1. many thousands of ringlets,
  2. some rings elliptical
  3. F-ring very narrow & braided
  4. rings very thin (< 2 km) kept from dispersing by "shepherd" moons
  5. "spokes" in rings which rotate like a solid body, with the same period as the planet (presumably tied to the magnetic field)

Many Moons: Titan, Mimas, Tethys, Janus, and Enceladus.

Credit: Erich Karkoschka (University of Arizona Lunar & Planetary Lab) and NASA

TITAN, 5150 km diameter, larger than earth's moon, has yellow atmosphere (CH4, NH3), Surface invisible
This composite was produced from images returned yesterday, 14 January 2005, by ESA's Huygens probe during its successful descent to land on Titan. It shows a full 360-degree view around Huygens. The left-hand side, behind Huygens, shows a boundary between light and dark areas. The white streaks seen near this boundary could be ground 'fog' of methane or ethane vapour, as they were not immediately visible from higher altitudes. As the probe descended, it drifted over a plateau (centre of image) and was heading towards its landing site in a dark area (right). This dark area is possibly a drainage channel which might still contain liquid material. From the drift of the probe, the wind speed has been estimated at around 6-7 metres per second. These images were taken from an altitude of about 8 kilometres with a resolution of about 20 metres per pixel.

Credits: ESA/NASA/JPL/University of Arizona

Touching down at 4.5 meters per second (16 kilometers per hour), the saucer-shaped probe is believed to have penetrated 15 centimeters or so into a surface with the consistency of wet sand or clay. Huygen's batteries are now exhausted but the probe transmitted data for more than 90 minutes after landing. Titan's bizarre chemical environment may bear similarities to planet Earth's before life evolved. Titan Landscape

Credit: ESA, NASA, Descent Imager/Spectral Radiometer Team (LPL)

Iapetus 1460 km diameter, has dark & light side.

Credit: NASA, Voyager, Copyright Calvin J. Hamilton

JANUS is two moons in orbit round each other.


Uranus

Pale green.
Uranus rotates on side.
Note no bands, deep clear atmosphere.


5 major moons: Ariel, Miranda, Titania, Oberon, and Umbriel.
Ariel from a distance of 170,000 kilometers.
Miranda from 42,000 kilometers.

Ring system, probably 9 narrow dark rings (seen by occulting star)
THis is how it might look from Ariel


Neptune

Pale blue-green
Large dark spot


1 major moon, Triton has an atmosphere, and a retrograde orbit (captured asteroid?). Other smaller moons. Appearance similar to outer moons of Jupiter:
i.e. ice-covered rock.


Pluto

Pluto Originally found in a search for 9th planet, based on prediction due to the perturbations of Neptune's orbit. Actually closer than Neptune (till 1999!)
>Seen to be double planet: Pluto-Charon

Allows mass to be found very accurately:

M ∼ 1.1 × 1022 kg (less than our Moon). Hence far too small to cause perturbations in Neptune's orbit! so .....

No large (i.e. Earth-sized) planets within 100 A.U.



On to the Other Objects in The Solar System