Jupiter

Jupiter Facts

• Jupiter is the fifth planet from the Sun and by far the largest:
  • distance from Sun: 778,330,000 km (5.20 AU)
  • equatorial diameter: 142,984 km; polar diameter: 133,708 km
  • mass: 1.900e27 kg

  Jupiter is more than twice as massive as all the other planets combined (318 times Earth).

• Jupiter (a.k.a. Jove; Greek Zeus) was the King of the Gods, the ruler of Olympus and the patron of the Roman state. Zeus was the son of Cronus (Saturn).

• Jupiter is the fourth brightest object in the sky (after the Sun, the Moon and Venus; at some times Mars is also brighter). It has been known since prehistoric times. Galileo's discovery, in 1610, of Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) was the first discovery of a center of motion not apparently centered on the Earth. It was a major point in favor of Copernicus's heliocentric theory of the motions of the planets; Galileo's outspoken support of the Copernican theory got him arrested by the Inquisition. He was forced to recant his beliefs and was imprisoned for the rest of his life.

• Jupiter was first visited by Pioneer 10 in 1973 and later by Pioneer 11, Voyager 1, Voyager 2 and Ulysses. The spacecraft Galileo is currently in orbit around Jupiter and will be sending back data for at least the next two years.

• The gas planets do not have solid surfaces, their gaseous material simply gets denser with depth (the radii and diameters quoted for the planets are for levels corresponding to a pressure of 1 atmosphere). What we see when looking at these planets is the tops of clouds high in their atmospheres (slightly above the 1 atmosphere level).

• Jupiter is about 90% hydrogen and 10% helium (by numbers of atoms, 75/25% by mass) with traces of methane, water, ammonia and "rock". This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium.

Jupiter's Satellites

Jupiter has 16 known satellites, the four large Galilean moons and 12 small ones.

• Jupiter is very gradually slowing down due to the tidal drag produced by the Galilean satellites. Also, the same tidal forces are changing the orbits of the moons, very slowly forcing them farther from Jupiter.

• Io, Europa and Ganymede are locked together by tidal forces into a 1:2:4 orbital resonance and their orbits evolve together. Callisto is almost part of this as well. In a few hundred million years, Callisto will be locked in too, orbiting at exactly twice the period of Ganymede and eight times the period of Io.

• Jupiter's satellites are named for other figures in the life of Zeus (mostly his lovers).

           Distance  Radius    Mass
Satellite  (000 km)   (km)     (kg)   Discoverer   Date
---------  --------  ------  -------  ----------  -----
Metis           128      20  9.56e16  Synnott      1979
Adrastea        129      10  1.91e16  Jewitt       1979
Amalthea        181      98  7.17e18  Barnard      1892
Thebe           222      50  7.77e17  Synnott      1979
Io              422    1815  8.94e22  Galileo      1610
Europa          671    1569  4.80e22  Galileo      1610
Ganymede       1070    2631  1.48e23  Galileo      1610
Callisto       1883    2400  1.08e23  Galileo      1610
Leda          11094       8  5.68e15  Kowal        1974
Himalia       11480      93  9.56e18  Perrine      1904
Lysithea      11720      18  7.77e16  Nicholson    1938
Elara         11737      38  7.77e17  Perrine      1905
Ananke        21200      15  3.82e16  Nicholson    1951
Carme         22600      20  9.56e16  Nicholson    1938
Pasiphae      23500      25  1.91e17  Melotte      1908
Sinope        23700      18  7.77e16  Nicholson    1914

Values for the smaller moons are approximate.

Amalthea

• MEAN RADIUS: 67 x 131 km
• MASS: ? (Earth=1)
• DENSITY: ? (gm/cm)
• GRAVITY: ? (Earth=1)
• ORBIT PERIOD: 0.498 (Earth days)
• ROTATION PERIOD: 0.498 (Earth days)
• SEMIMAJOR AXIS OF ORBIT: 181,300 km
• ECCENTRICITY OF ORBIT: 0.003

Callisto

• MEAN RADIUS: 2404 km
• MASS: 0.0179 (Earth=1)
• DENSITY: 1.81 (gm/cm)
• GRAVITY: 0.124 (Earth=1)
• ORBIT PERIOD: 16.689 (Earth days)
• ROTATION PERIOD: 16.689 (Earth days)
• SEMIMAJOR AXIS OF ORBIT: 1,883,000 km
• ECCENTRICITY OF ORBIT: 0.007

Europa

• MEAN RADIUS: 1565 km
• MASS: 0.0081 (Earth=1)
• DENSITY: 3.04 (gm/cm)
• GRAVITY: 0.138 (Earth=1)
• ORBIT PERIOD: 3.551 (Earth days)
• ROTATION PERIOD: 3.551 (Earth days)
• SEMIMAJOR AXIS OF ORBIT: 670,900 km
• ECCENTRICITY OF ORBIT: 0.009

Ganymede

• MEAN RADIUS: 2634 km
• MASS: 0.0175 (Earth=1)
• DENSITY: 1.93 (gm/cm)
• GRAVITY: 0.145 (Earth=1)
• ORBIT PERIOD: 7.155 (Earth days)
• ROTATION PERIOD: 7.155 (Earth days)
• SEMIMAJOR AXIS OF ORBIT: 1,070,00 km
• ECCENTRICITY OF ORBIT: 0.002

Io

• MEAN RADIUS: 1830 km
• MASS: 0.0149 (Earth=1)
• DENSITY: 3.55 (gm/cm)
• GRAVITY: 0.138 (Earth=1)
• ORBIT PERIOD: 1.769 (Earth days)
• ROTATION PERIOD: 1.769 (Earth days)
• SEMIMAJOR AXIS OF ORBIT: 422,600 km
• ECCENTRICITY OF ORBIT: 0.004

Jupiter's Rings

          Distance   Width   Mass
Ring      (km)        (km)   (kg)
----      --------   -----  ------
Halo      100000     22800   ?
Main      122800      6400  1e13
Gossamer  129200    850000   ?

(distance is from Jupiter's center to the ring's inner edge)