orbit: 778,330,000 km (5.20 AU) from Sun
diameter: 142,984 km (equatorial)
mass: 1.900e27 kg
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
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.
Our knowledge of the interior of Jupiter (and the other gas planets) is
highly indirect and likely to remain so
for some time. (The data from Galileo's atmospheric probe goes down only about 150 km below the cloud
Jupiter probably has a core of rocky material amounting to something like
10 to 15 Earth-masses. Above
the core lies the main bulk of the planet in the form of liquid metallic hydrogen. This exotic form of the most
common of elements is possible only at pressures exceeding 4 million bars, as is the case in the interior of
Jupiter (and Saturn). Liquid metallic hydrogen consists of ionized protons and electrons (like the interior of
the Sun but at a far lower temperature). At the temperature and pressure of Jupiter's interior hydrogen is a
liquid, not a gas. It is an electrical conductor and the source of Jupiter's magnetic field. This layer probably
also contains some helium and traces of various "ices".
The outermost layer is composed primarily of ordinary molecular hydrogen
and helium which is liquid in the
interior and gaseous further out. The atmosphere we see is just the very top of this deep layer. Water, carbon
dioxide, methane and other simple molecules are also present in tiny amounts.
Three distinct layers of clouds are believed to exist consisting of ammonia
ice, ammonium hydrosulfide
and a mixture of ice and water. However, the preliminary results from the Galileo probe show only faint
indications of clouds (one instrument seems to have detected the topmost layer while another may have
seen the second). But the probe's entry point was unusual -- Earth-based telescopic observations and more
recent observations by the Galileo orbiter suggest that the probe entry site may well have been one of the
warmest and least cloudy areas on Jupiter at that time.
Data from the Galileo atmospheric probe also indicate that there is much
less water than expected. The
expectation was that Jupiter's atmosphere would contain about twice the amount of oxygen (combined with
the abundant hydrogen to make water) as the Sun. But it now appears that the actual concentration much
less than the Sun's. Also surprising was the high temperature and density of the uppermost parts of the
Jupiter and the other gas planets have high velocity winds which are confined
in wide bands of latitude.
The winds blow in opposite directions in adjacent bands. Slight chemical and temperature differences
between these bands are responsible for the colored bands that dominate the planet's appearance. The light
colored bands are called zones; the dark ones belts. The bands have been known for some time on Jupiter,
but the complex vortices in the boundary regions between the bands were first seen by Voyager. The data
from the Galileo probe indicate that the winds are even faster than expected (more than 400 mph) and
extend down into as far as the probe was able to observe; they may extend down thousands of kilometers
into the interior. Jupiter's atmosphere was also found to be quite turbulent. This indicates that Jupiter's winds
are driven in large part by its internal heat rather than from solar input as on Earth.
The vivid colors seen in Jupiter's clouds are probably the result of subtle
chemical reactions of the trace
elements in Jupiter's atmosphere, perhaps involving sulfur whose compounds take on a wide variety of
colors, but the details are unknown.
The colors correlate with the cloud's altitude: blue lowest, followed by
browns and whites, with reds highest.
Sometimes we see the lower layers through holes in the upper ones.
The Great Red Spot (GRS) has been seen by Earthly observers for more than
300 years (its discovery is
usually attributed to Cassini, or Robert Hooke in the 17th century). The GRS is an oval about 12,000 by
25,000 km, big enough to hold two Earths. Other smaller but similar spots have been known for decades.
Infrared observations and the direction of its rotation indicate that the GRS is a high-pressure region whose
cloud tops are significantly higher and colder than the surrounding regions. Similar structures have been
seen on Saturn and Neptune. It is not known how such structures can persist for so long.
Jupiter radiates more energy into space than it receives from the Sun.
The interior of Jupiter is hot: the core
is probably about 20,000 K. The heat is generated by the Kelvin-Helmholtz mechanism, the slow
gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun; it
is much too small and hence its interior is too cool to ignite nuclear reactions.) This interior heat probably
causes convection deep within Jupiter's liquid layers and is probably responsible for the complex motions
we see in the cloud tops. Saturn and Neptune are similar to Jupiter in this respect, but oddly, Uranus is not.
Jupiter is just about as large in diameter as a gas planet can be. If more
material were to be added, it would
be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only
because of its internal (nuclear) heat source. (But Jupiter would have to be at least 80 times more massive to
become a star.)
Jupiter has a huge magnetic field, much stronger than Earth's. Its magnetosphere
extends more than 650
million km (past the orbit of Saturn!). (Note that Jupiter's magnetosphere is far from spherical -- it extends
"only" a few million kilometers in the direction toward the Sun.) Jupiter's moons therefore lie within its
magnetosphere, a fact which may partially explain some of the activity on Io. Unfortunately for future space
travelers and of real concern to the designers of the Voyager and Galileo spacecraft, the environment near
Jupiter contains high levels of energetic particles trapped by Jupiter's magnetic field. This "radiation" is
similar to, but much more intense than, that found within Earth's Van Allen belts. It would be immediately fatal
to an unprotected human being.
The Galileo atmospheric probe discovered a new intense radiation belt between
Jupiter's ring and the
uppermost atmospheric layers. This new belt is approximately 10 times as strong as Earth's Van Allen
radiation belts. Surprisingly, this new belt was also found to contain high energy helium ions of unknown
Jupiter has faint rings like Saturn's, but much smaller (right). They were
totally unexpected and were only
discovered when two of the Voyager 1 scientists insisted that after traveling 1 billion km it was at least worth
a quick look to see if any rings might be present. Everyone else thought that the chance of finding anything
was nil, but there they were. It was a major coup. They have since been imaged in the infra-red from
Unlike Saturn's, Jupiter's rings are dark (albedo about .05). They're probably
composed of very small grains
of rocky material.
Particles in Jupiter's rings probably don't stay there for long (due to
atmospheric and magnetic drag).
Therefore, if the rings are permanent features, they must be continuously resupplied. The small satellites
Metis and Adrastea, which orbit within the rings, are the obvious candidate sources.
In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with spectacular
results. The effects were
clearly visible even with amateur telescopes. The debris from the collision was visible for nearly a year
afterward with HST.
When it is in the nighttime sky, Jupiter is often the brightest "star"
in the sky (it is second only to Venus, which
is seldom visible in a dark sky). The four Galilean moons are easily visible with binoculars; a few bands and
the Great Red Spot can be seen with a small astronomical telescope.
1.90 x 10^27
Diameter (km) 142,800
Mean density (kg/m^3) 1314
Escape velocity (m/sec) 59500
Volume (km^3) 144,559,280
Gravity (eq., 1 bar) (m/s^2) 23.12
Radius (1 bar level) (km)
GM (x 106 km^3/s^2)
Bond albedo 0.70
Visual geometric albedo 0.52
Visual magnitude V(1,0) -9.40
Solar irradiance (W/m^2) 51.
Black-body temperature (K) 90.6
Moment of inertia (I/MR^2 0.254
J2 (x 10^-6) 14,736
Average distance from Sun (AU)
Rotation period (length of day in Earth hours) 9.8
Revolution period (length of year in Earth years) 11.86
Obliquity (tilt of axis in degrees)
Orbit inclination (degrees) 1.3
Orbit eccentricity (deviation from circular) 0.048
Mean surface temperature (K) 120 (cloud tops)
Rings Faint ring. Infrared spectra imply dark rock fragments.
Semimajor axis (km)
778.3 x (10^6)
Sidereal orbit period (days) 4,332.589
Tropical orbit period (days) 4,330.595
Perihelion (km) 740.6 x (10^6)
Aphelion (km) 816.0 x (10^6)
Synodic period (days) 398.88
Mean orbital velocity (km/s) 13.07
Orbit inclination (deg) 1.305
Orbit eccentricity 0.04845
Sidereal rotation period (hours) 9.9250*
Obliquity to orbit (deg) 3.12
* System III (1965.0) coordinates
Goddard Space Flight Center O4 Model
Dipole field strength:
Dipole tilt to rotational axis: 9.6 degrees
Longitude of tilt: 201.7 degrees
Dipole offset (planet center to dipole center) distance: 0.131 Rj
Latitude/Longitude of offset vector: -8.0 degrees/148.57 degrees
Note: All latitudes/longitudes are given in Jovian System III (1965.0)
Rj denotes Jovian radii, 71,398 km
Surface Pressure: >>100 bars
Average temperature: ~129 K
Temperature at 1 bar: ~165 K
Density at 1 bar: ~0.16 kg/m3
Up to ~150 m/s (<30 degrees latitude)
Up to ~40 m/s (>30 degrees latitude)
Scale height: 27 km
Mean molecular weight: 2.22 g/mole
Major: Molecular hydrogen (H2) - 89%; Helium (He) - 11%
Minor (ppm): Methane (CH4) - ~2000; Ammonia (NH3) - ~200;
Hydrogen Deuteride (HD) - 20; Ethane (C2H6) - ~5;
Water (H2O) - 1
Aerosols: Ammonia ice, water ice, ammonia
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
|Satellite||Distance (km)||Radius (km)||Mass (kg)||Discoverer||Date|
|Ring||Distance (km)||Width (km)||Mass (kg)|