is the fifth planet from the Sun and by far the largest. Jupiter is more
than twice as massive as all the other planets combined (318 times Earth).
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 in trouble with the Inquisition.
Jupiter was first visited by
Pioneer 10 in 1973 and later by Pioneer 11, Voyager 1, Voyager 2 and
Ulysses. The spacecraft Galileo orbited Jupiter for eight years.
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
Nebula from which the entire solar system was formed. Saturn
has a similar composition, but Uranus
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
goes down only about 150 km below the cloud tops.)
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.
experiments have shown that hydrogen does not change phase suddenly.
Therefore the interiors of the jovian planets probably have indistinct
boundaries between their various interior layers.
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 (left) 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.
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 atmosphere.
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
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
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 origin.
Jupiter has rings
like Saturn's, but much fainter and 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 ground-based telescopes and by Galileo.
Unlike Saturn's, Jupiter's
rings are dark (albedo
about .05). They're probably composed of very small grains of rocky
material. Unlike Saturn's rings, they seem to contain no ice.
Particles in Jupiter's rings
probably don't stay there for long (due to atmospheric and magnetic drag).
The Galileo spacecraft found clear evidence that the rings are
continuously resupplied by dust formed by micrometeor impacts on the four inner
moons, which are very energetic because of Jupiter's large
gravitational field. The inner halo ring is broadened by interactions with
Jupiter's magnetic field.
In July 1994, Comet
Shoemaker-Levy 9 collided with Jupiter with spectacular results
(left). 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. There are
sites that show the current position of Jupiter (and the other
planets) in the sky. More detailed and customized charts can be created
with a planetarium
program such as Starry
Jupiter has 61 known satellites (as of May 2003): the four large Galilean
moons, 34 smaller named ones, plus many more small ones discovered
recently but not yet named:
- 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
- Io, Europa and Ganymede are locked together in 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 (eight times the
period of Io).
- Jupiter's satellites are named for other figures in the life of Zeus
(mostly his lovers).
- Many more
small moons have been discovered recently but have not as yet been
officially confirmed or named. The most up to date info on them can be
found at Scott
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
Crme 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. Many more small moons are
not listed here.
Distance Width Mass
Ring (km) (km) (kg)
---- -------- ----- ------
Halo 100000 22800 ?
Main 122800 6400 1e13
Gossamer 129200 214200 ?
(distance is from Jupiter's center to the ring's inner edge)
atmospheric probe provides our first direct measurements of Jupiter's
atmosphere, our first real data about the chemistry of a gas planet.
The initial data indicate a major new mystery -- why is there so
little water in Jupiter's atmosphere? There is a building consensus
that the probe encountered an unusually dry area but more details are
- Just how deep into the interior do the zonal winds extend? What
mechanism drives them?
- Why is the GRS so persistent? There are actually several theoretical
models that seem to work. We need more data to decide between them.
- How can we get more direct information about the interior? Liquid
metallic hydrogen has been produced
in a lab at Lawrence Livermore National Laboratory but much about
its properties is still unknown.
- Why are Jupiter's rings so dark while Saturn's are so bright?
Super-Thunderstorms on Jupiter
For 400 years scientists have puzzled over the swirling and
turbulent clouds on Jupiter. Now the giant planet's secret is out.
information provided by Cornell University
Anvil clouds tower
more than 30 miles high. Amid the gathering gloom, 100 mph winds whip
clouds across the sky. Painfully brilliant lightning flashes punctuate the
tumult. Meanwhile, clouds from another giant storm dump several inches of
water, every day, over an area more than 600 miles across.
giant planet is 1300 times larger than Earth
Given the supernatural severity of these storms, and thunderheads three
times higher than we see on our planet, we are clearly not on the Earth.
Welcome to the super-storms of Jupiter.
The giant planet of the Solar System is as different from the Earth as
any planet could be. Jupiter is big enough to fit 1300 Earths inside, and
it is made of gas and liquid throughout. Yet some of its storms are
remarkably similar - though vaster in scale - to thunderstorms on Earth.
Even stranger, the latest results from NASA's Galileo spacecraft reveal
that these storms are powered in a completely different way from
"There is a lot of activity we see on Jupiter that we see on
Earth," says Peter J. Gierasch, professor of astronomy at Cornell
University. Along with colleagues from Cornell, the California Institute
of Technology and NASA's Jet Propulsion Laboratory, Gierasch has been
studying views of Jupiter taken by Galileo on May 4, 1999. He continues:
"We see jet streams, large cyclonic elements, large anti-cyclonic
elements and many elements of unpredictability and turbulence."
Of all the tempest-tossed storms in the Solar System, the astronomers
chose to examine an area west of the giant planet's Great Red Spot, in a
region known as the South Equatorial Belt. The images were part of a
planned effort to search for local convection, and study its details.
storm centers are visible in these Galileo images.
The false colors show how deep the clouds lie in Jupiter's
atmosphere: the highest appear blue, intermediate clouds green and
the deepest clouds red.
A lightning strike (blue) is overlaid. It was photographed while
the same storm was on the night side of the planet.
The short lines show wind speeds.
They discovered that some of the storms here closely resemble clusters
of thunderstorms found on Earth - mesoscale convective complexes. What is
remarkable about the storm complexes on Jupiter, says Gierasch, is that
they have the same physics as thunderstorm clusters on Earth, but they are
generated by a completely different type of heat source. Generally,
thunderstorms on Earth are small individual cells of cumulonimbus clouds,
caused by summertime heat from the Sun. A mesoscale convective complex is
a cluster of many cells of thunderstorms, of the type that commonly
strikes the midwestern United States. These complexes are also formed by
intense summertime heat.
The Sun's heat drives other weather patterns on Earth, of course, such
as hurricanes and cyclones. The difference is the source of the system's
'fuel'. Hurricanes and cyclones on Earth are fueled by the warm ocean.
Mesoscale convective complexes develop because of an instability in the
atmosphere. Where it is warm near the Earth's surface in the summer and
cooler aloft, condensation rises and forms many cells of intense
thunderclouds over a vast area. These summertime giants can last for
hours, even days, and dump unusually large amounts of rain.
violent storms on Jupiter are driven by the immense heat from the
On Jupiter, the colossal mesoscale convective complexes also last from
12 hours to several Earth days, producing correspondingly huge deluges of
rain over vast areas. The new results show that - contrary to previous
belief - these thunderstorm complexes are not fuelled by the Sun's heat,
but instead develop from the intense heat emanating from Jupiter's core.
The giant planet lies five times further from the Sun than the Earth,
so it receives much less solar heat. On the other hand, Jupiter's core is
extremely hot. It still retains heat from the planet's original formation
by collapse and compression of the planet's huge gaseous bulk. "It is
in the process of cooling, and it will likely continue to cool for at
least another five billion years," Gierasch says.
Heat leaks upwards from a reservoir of highly compressed hydrogen in
the planet's center, so this gaseous giant emits nearly 70 percent more
heat than it absorbs from the Sun. The source of the stormy turbulence on
Jupiter thus seems to be the planet itself.
Mesoscale convective complexes on Earth are riven with lightning, seen
dramatically from the space shuttle. What about Jupiter's giant storm
systems? Galileo's instruments are not able to detect lightning on the
planet's sunlit side. But once the storm crosses into the dark side,
astronomers are able to see the lightning and confirm the existence of
Jupiter's mesoscale convective complexes .
Great Red Spot is the most powerful thunderstorm in the Solar
These lightning bolts dwarf anything on Earth, according to Andrew. P.
Ingersoll of the California Institute of Technology and Blaine Little of
ITRES Research, Calgary, Canada. They have measured the Jovian lightning
strokes as several times the size of the largest terrestrial bolts.
Jupiter's storms are
not only spectacular. The new Galileo results suggest that the mesoscale
convective complexes provide the energy that drives the whole of Jupiter's
powerful weather system. It's an almost-continuous cycle, Gierasch
explains. The storms develop and drop rain; the raindrops evaporate prior
to reaching Jupiter's core heat-source, and rise again as water vapour
that convect upwards to start the next round of storms.
In the 400 years
since the Italian astronomer Galileo first turned his telescope towards
Jupiter, astronomers have puzzled over its spectacular bands and whorls of
swirling clouds. Now the giant planet's secret is out. Its turbulent
clouds and ferocious weather systems are fueled by its hidden superhot
core, and driven by the greatest thunderstorms in the Solar System.
You can find out
more about physics at Cornell University on their webpage.
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