Download Jupiter Jupiter is the largest planet in the solar system. Its diameter is

Jupiter
Jupiter is the largest planet in the solar system.
Its diameter is 88,846 miles (142,984
kilometers), more than 11 times that of Earth,
and about one-tenth that of the sun. It would
take more than 1,000 Earths to fill up the
volume of the giant planet. When viewed from
Earth, Jupiter appears brighter than most stars. It
is usually the second brightest planet -- after
Venus.
Jupiter is the fifth planet from the sun. Its mean
(average) distance from the sun is about
483,780,000 miles (778,570,000 kilometers),
more than five times Earth's distance. Ancient
astronomers named Jupiter after the king of the
Roman gods.
Astronomers have studied Jupiter with
telescopes based on Earth and aboard artificial
satellites in orbit around Earth. In addition, the
The layers of dense clouds around Jupiter
appear in a photograph of the planet
taken by the Voyager 1 space probe. The
large, oval-shaped mark on the clouds is
the Great Red Spot. The spot is believed to
be an intense atmospheric disturbance.
Image credit: Jet Propulsion Laboratory
United States has sent six space probes (crewless
exploratory craft) to Jupiter.
Astronomers witnessed a spectacular event in
July 1994, when 21 fragments of a comet named
Shoemaker-Levy 9 crashed into Jupiter's
atmosphere. The impacts caused tremendous
explosions, some scattering debris over areas
larger than the diameter of Earth.
Physical features of Jupiter
Jupiter is a giant ball of gas and liquid with little,
if any, solid surface. Instead, the planet's surface
is composed of dense red, brown, yellow, and
white clouds. The clouds are arranged in lightcolored areas called zones and darker regions
called belts that circle the planet parallel to the
equator.
Orbit and rotation
Jupiter travels around the sun in a slightly
elliptical (oval-shaped) orbit. The planet
completes one orbit in 4,333 Earth days, or
almost 12 Earth years.
As Jupiter orbits the sun, the planet rotates on its
axis, an imaginary line through its center. The
axis is tilted about 3¡. Scientists measure tilt
relative to a line at a right angle to the orbital
plane, an imaginary surface touching all points
of the orbit.
Jupiter rotates faster than any other planet. It
takes 9 hours 56 minutes to spin around once on
its axis, compared with 24 hours for Earth.
Scientists cannot measure the rotation of the
interior of the giant planet directly, so they have
calculated the speed from indirect
measurements. They first calculated the speed
using an average of the speeds of the visible
clouds that move with interior currents, except
for a more rapid zone near the equator.
Jupiter sends out radio waves strong enough to
be picked up by radio telescopes on Earth.
Scientists now measure these waves to calculate
Jupiter's rotational speed. The strength of the
waves varies under the influence of Jupiter's
magnetic field in a pattern that repeats every 9
hours 56 minutes. Because the magnetic field
originates in Jupiter's core, this variation shows
how fast the plant's interior spins.
Jupiter's rapid rotation makes it bulge at the
equator and flatten at the poles. The planet's
diameter is about 7 percent larger at the equator
than at the poles.
Mass and density
Jupiter is heavier than any other planet. Its mass
(quantity of matter) is 318 times larger than that
of Earth. Although Jupiter has a large mass, it
has a relatively low density. Its density averages
1.33 grams per cubic centimeter, slightly more
than the density of water. The density of Jupiter
is about 1/4 that of Earth. Because of Jupiter's
low density, astronomers believe that the planet
consists primarily of hydrogen and helium, the
lightest elements. Earth, on the other hand, is
made up chiefly of metals and rock. Jupiter's
mix of chemical elements resembles that of the
sun, rather than that of Earth.
Jupiter may have a core made up of heavy
elements. The core may be of about the same
chemical composition as Earth, but 20 or 30
times more massive.
The force of gravity at the surface of Jupiter is
up to 2.4 times stronger than on Earth. Thus, an
object that weighs 100 pounds on Earth would
weigh as much as 240 pounds on Jupiter.
The atmosphere of Jupiter is composed of about
86 percent hydrogen, 14 percent helium, and
tiny amounts of methane, ammonia, phosphine,
water, acetylene, ethane, germanium, and carbon
monoxide. The percentage of hydrogen is based
on the number of hydrogen molecules in the
atmosphere, rather than on their total mass.
Scientists have calculated these amounts from
measurements taken with telescopes and other
instruments on Earth and aboard spacecraft.
These chemicals have formed colorful layers of
clouds at different heights. The highest white
clouds in the zones are made of crystals of
frozen ammonia. Darker, lower clouds of other
chemicals occur in the belts. At the lowest levels
that can be seen, there are blue clouds.
Astronomers had expected to detect water
clouds about 44 miles (70 kilometers) below the
ammonia clouds. However, none have been
discovered at any level.
Jupiter's most
outstanding
surface
feature is the
Great Red
Spot, a
swirling mass
of gas
resembling a
hurricane.
The widest
The planet Jupiter's Great Red
diameter of Spot is a huge mass of swirling
the spot is
gas. At its widest, it is about three
about three
times the diameter of the Earth.
times that of Image credit: NASA
Earth. The
color of the spot usually varies from brick-red to
slightly brown. Rarely, the spot fades entirely.
Its color may be due to small amounts of sulfur
and phosphorus in the ammonia crystals.
The edge of the Great Red Spot circulates at a
speed of about 225 miles (360 kilometers) per
hour. The spot remains at the same distance
from the equator but drifts slowly east and west.
The zones, belts, and the Great Red Spot are
much more stable than similar circulation
systems on Earth. Since astronomers began to
use telescopes to observe these features in the
late 1600's, the features have changed size and
brightness but have kept the same patterns.
Temperature
The temperature at the top of Jupiter's clouds is
about -230 degrees F (-145 degrees C).
Measurements made by ground instruments and
spacecraft show that Jupiter's temperature
increases with depth below the clouds. The
temperature reaches 70 degrees F (21 degrees C)
-- "room temperature" -- at a level where the
atmospheric pressure is about 10 times as great
as it is on Earth. Scientists speculate that if
Jupiter has any form of life, the life form would
reside at this level. Such life would need to be
airborne, because there is no solid surface at this
location on Jupiter. Scientists have discovered
no evidence for life on Jupiter.
Near the planet's center, the temperature is much
higher. The core temperature may be about
43,000 degrees F (24,000 degrees C) -- hotter
than the surface of the sun.
Jupiter is still losing the heat produced when it
became a planet. Most astronomers believe that
the sun, the planets, and all the other bodies in
the solar system formed from a spinning cloud
of gas and dust. The gravitation of the gas and
dust particles packed them together into dense
clouds and solid chunks of material. By about
4.6 billion years ago, the material had squeezed
together to form the various bodies in the solar
system. The compression of material produced
heat. So much heat was produced when Jupiter
formed that the planet still radiates about twice
as much heat into space as it receives from
sunlight.
Magnetic field
Like Earth and many other planets, Jupiter acts
like a giant magnet. The force of its magnetism
extends far into space in a region surrounding
the planet called its magnetic field. Jupiter's
magnetic field is about 14 times as strong as
Earth's, according to measurements made by
spacecraft. Jupiter's magnetic field is the
strongest in the solar system, except for fields
associated with sunspots and other small regions
on the sun's surface.
Scientists do not fully understand how planets
produce magnetic fields. They suspect, however,
that the movement of electrically charged
particles in the interior of planets generates the
fields. Jupiter's field would be so much stronger
than Earth's because of Jupiter's greater size and
faster rotation.
Jupiter's magnetic field traps electrons, protons,
and other electrically charged particles in
radiation belts around the planet. The particles
are so powerful that they can damage
instruments aboard spacecraft operating near the
planet.
Within a region of space called the
magnetosphere, Jupiter's magnetic field acts as a
shield. The field protects the planet from the
solar wind, a continuous flow of charged
particles from the sun. Most of these particles
are electrons and protons traveling at a speed of
about 310 miles (500 kilometers) per second.
The field traps the charged particles in the
radiation belts. The trapped particles enter the
magnetosphere near the poles of the magnetic
field. On the side of the planet away from the
sun, the magnetosphere stretches out into an
enormous magnetic tail, often called a
magnetotail, that is at least 435 million miles
(700 million kilometers) long.
Radio waves given off by Jupiter reach radio
telescopes on Earth in two forms -- bursts of
radio energy and continuous radiation. Strong
bursts occur when Io, the closest of Jupiter's four
large moons, passes through certain regions in
the planet's magnetic field. Continuous radiation
comes from Jupiter's surface as well as from
high-energy
particles in
the radiation
belts.
Satellites
Jupiter has 16
satellites that
measure at
least 6 miles
(10
kilometers) in
diameter. It
also has many Callisto, a moon of Jupiter, is
covered with craters produced
smaller
when asteroids and comets struck
satellites.
Jupiter's four its icy surface. Beneath the
surface may be an ocean of salty
largest
satellites, in liquid water. Image credit: NASA
order of their distance from Jupiter, are Io,
Europa, Ganymede, and Callisto. These four
moons are called the Galilean satellites. The
Italian astronomer Galileo discovered them in
1610 with one of the earliest telescopes.
Io has many active volcanoes, which produce
gases containing sulfur. The yellow-orange
surface of Io probably consists largely of solid
sulfur that
was
deposited
by the
eruptions.
Europa
ranks as the
smallest of
the Galilean
satellites,
with a
diameter of
1,945 miles
(3,130
kilometers).
Europa has
a smooth,
cracked, icy
surface.
Scars from the crash of Comet
Shoemaker-Levy 9 appear on
Jupiter's surface as a series of
maroon blotches in this photo.
The comet broke into 21 pieces
before it hit Jupiter in 1994.
Image credit: Hubble Space
The largest
Telescope Comet Team and NASA Galilean
satellite is Ganymede, with a diameter of 3,273
miles (5,268 kilometers). Ganymede is larger
than the planet Mercury. Callisto, with a
diameter of 2,986 miles (4,806 kilometers), is
slightly smaller than Mercury. Ganymede and
Callisto appear to consist of ice and some rocky
material. The two satellites have many craters.
Jupiter's remaining satellites are much smaller
than the Galilean moons. Amalthea and Himalia
are the next largest. Potato-shaped Amalthea is
about 163 miles (262 kilometers) in its long
dimension. Himalia is 106 miles (170
kilometers) in diameter. Most of the remaining
satellites were discovered by astronomers using
large telescopes on Earth. Scientists discovered
Metis and Adrastea in 1979 by studying pictures
that had been taken by the Voyager spacecraft.
Rings
Jupiter has three thin rings around its equator.
They are much fainter than the rings of Saturn.
Jupiter's rings appear to consist mostly of fine
dust particles. The main ring is about 20 miles
(30 kilometers) thick and more than 4,000 miles
(6,400 kilometers) wide. It circles the planet
inside the orbit of Amalthea.
The impact of Comet Shoemaker-Levy 9
In March 1993, astronomers Eugene Shoemaker,
Carolyn Shoemaker, and David H. Levy
discovered a comet near Jupiter. The comet,
later named Shoemaker-Levy 9, probably once
orbited the sun independently, but had been
pulled by Jupiter's gravity into an orbit around
the planet. When the comet was discovered, it
had broken into 21 pieces. The comet probably
had broken apart when it passed close to Jupiter.
Calculations based on the comet's location and
velocity showed that the fragments would crash
into Jupiter's atmosphere in July 1994. Scientists
hoped to learn much about the effects of a
collision between a planet and a comet.
Astronomers at all the major telescopes on Earth
turned their instruments toward Jupiter at the
predicted collision times. Scientists also
observed Jupiter with the powerful Hubble
Space Telescope, which is in orbit around Earth;
and the remotely controlled space probe Galileo,
which was on its way to Jupiter.
The fragments fell on the back side of Jupiter as
viewed from Earth and the Hubble Space
Telescope. But the rotation of Jupiter carried the
impact sites around to the visible side after less
than half an hour. Scientists estimate that the
largest fragments were about 0.3 to 2.5 miles
(0.5 to 4 kilometers) in diameter. The impacts
were directly observable from Galileo, which
was within about 150 million miles (240 million
kilometers) from Jupiter. However, damage to
certain of the probe's instruments limited its
ability to record and send data.
The impacts caused large explosions, probably
due to the compression, heating, and rapid
expansion of atmospheric gases. The explosions
scattered comet debris over large areas, some
with diameters larger than that of Earth. The
debris gradually spread into a dark haze of fine
material that remained suspended for several
months in Jupiter's upper atmosphere. If a
similar comet ever collided with Earth, it might
produce a haze that would cool the atmosphere
and darken the planet by absorbing sunlight. If
the haze lasted long enough, much of Earth's
plant life could die, along with the people and
animals that depend on plants.
Flights to Jupiter
The United States has sent six space probes to
Jupiter: (1) Pioneer 10, (2) Pioneer-Saturn, (3)
Voyager 1, (4) Voyager 2, (5) Ulysses, and (6)
Galileo.
Pioneer 10 was launched in 1972 and flew
within 81,000 miles (130,000 kilometers) of
Jupiter on Dec. 3, 1973. The probe revealed the
severe effects of Jupiter's radiation belt on
spacecraft. Pioneer 10 also reported the amount
of hydrogen and helium in the planet's
atmosphere. In addition, the probe discovered
that Jupiter has an enormous magnetosphere.
Pioneer-Saturn flew within 27,000 miles (43,000
kilometers) of Jupiter in December 1974. The
craft provided close-up photographs of Jupiter's
polar regions and data on the Great Red Spot,
the magnetic field, and atmospheric
temperatures.
Voyager 1 and Voyager 2 flew past Jupiter in
March and July 1979, respectively. These craft
carried more sensitive instruments than did the
Pioneers, and transmitted much more
information. Astronomers used photographs
taken by the Voyagers to make the first detailed
maps of the Galilean satellites. The Voyagers
also revealed sulfur volcanoes on Io, discovered
lightning in Jupiter's clouds, and mapped flow
patterns in the cloud bands.
Ulysses was launched in October 1990 and
passed by Jupiter in February 1992. The
European Space Agency, an organization of
Western European nations, had built the probe
mainly to study the sun's polar regions.
Scientists used the tremendous gravitational
force of Jupiter to put Ulysses into an orbit that
would take it over the sun's polar regions. As
Ulysses passed by Jupiter, it gathered data
indicating that the solar wind has a much greater
effect on Jupiter's magnetosphere than earlier
measurements had suggested.
Galileo began
its journey to
Jupiter in
October
1989. The
craft released
an
atmospheric
probe in July
1995. In
December
Ganymede, a moon of Jupiter, has
1995, the
craters and cracks on its surface.
probe
Asteroids and comets that hit
plunged into Ganymede made the craters. The
Jupiter's
cracks are due to expansion and
atmosphere. contraction of the surface. Image
The probe
credit: NASA
penetrated
deep into the cloud layers and measured the
amount of water and other chemicals in the
atmosphere. Also in December 1995, Galileo
went into orbit around Jupiter. Over the next
several years, the craft monitored Jupiter's
atmosphere and observed the planet's major
satellites. Galileo's mission was extended in
1997 and again in 1999. Eventually, however,
the craft ran low on fuel. In September 2003,
mission managers intentionally crashed Galileo
into Jupiter's atmosphere to avoid any risk of the
craft crashing into and contaminating Jupiter's
moon Europa. Galileo's observations of Europa
had shown that it might have an ocean below its
surface capable of supporting life.
Contributors: Peter J. Gierasch, Ph.D.,
Professor of Astronomy, Cornell University.
Philip D. Nicholson, Ph.D., Professor of
Astronomy, Cornell University.
Gierasch, Peter J., and Philip D. Nicholson.
"Jupiter." World Book Online Reference Center.
2004. World Book, Inc.
(http://www.worldbookonline.com/wb/Article?id
=ar293080.)
Saturn
Saturn is the second largest planet. Only Jupiter
is larger. Saturn has seven thin, flat rings around
it. The rings consist of numerous narrow
ringlets, which are made up of ice particles that
travel around the planet. The gleaming rings
make Saturn one of the most beautiful objects in
the solar system. Jupiter, Neptune, and Uranus
are the only other planets known to have rings.
Their rings are much fainter than those around
Saturn.
90 degrees) to the planet's path around the sun.
The axis tilts at an angle of about 27 degrees
from the perpendicular position.
Saturn rotates faster than any other planet except
Jupiter. Saturn spins around once in only 10
hours 39 minutes, compared to about 24 hours,
or one day, for Earth. The rapid rotation of
Saturn causes the planet to bulge at its equator
and flatten at its poles. The planet's diameter is
8,000 miles (13,000 kilometers) larger at the
equator than between the poles.
Surface and atmosphere
Saturn is encircled by seven major rings.
In this photograph, a section of the rings
is hidden by the planet's shadow. The
Cassini spacecraft, launched in 1997 to
study Saturn and its rings and satellites,
captured this natural color image as it
approached the planet in 2004. Image
credit: NASA/JPL/Space Science Institute
Saturn's diameter at its equator is about 74,900
miles (120,540 kilometers), almost 10 times that
of Earth. The planet can be seen from Earth with
the unaided eye, but its rings cannot. Saturn was
the farthest planet from Earth that the ancient
astronomers knew about. They named it for the
Roman god of agriculture.
Saturn travels around the sun in an elliptical
(oval-shaped) orbit. Its distance from the sun
varies from about 941,070,000 miles
(1,514,500,000 kilometers) at its farthest point to
about 840,440,000 miles (1,352,550,000
kilometers) at its closest point. The planet takes
about 10,759 Earth days, or about 29 1/2 Earth
years, to go around the sun, compared with 365
days, or one year, for Earth.
Rotation
As Saturn travels around the sun, it spins on its
axis, an imaginary line drawn through its center.
Saturn's axis is not perpendicular (at an angle of
Most scientists believe Saturn is a giant ball of
gas that has no solid surface. However, the
planet seems to have a hot solid inner core of
iron and rocky material. Around this dense
central part is an outer core that probably
consists of ammonia, methane, and water. A
layer of highly compressed, liquid metallic
hydrogen surrounds the outer core. Above this
layer lies a region composed of hydrogen and
helium in a viscous (syruplike) form. The
hydrogen and helium become gaseous near the
planet's surface and merge with its atmosphere,
which
consists
chiefly of the
same two
elements.
A dense layer
of clouds
covers Saturn.
Photographs
of the planet
show a series
of belts and
zones of
varied colors Bands of clouds circle the planet
on the cloud Saturn. The large swirling spot is
a hurricane-like mass of gas
tops. This
1,900 miles (3,000 kilometers)
banded
across. Image credit: NASA
appearance
seems to be caused by differences in the
temperature and altitude of atmospheric gas
masses.
The plants and animals that live on Earth could
not live on Saturn. Scientists doubt that any
form of life exists on the planet.
Temperature
The tilt of Saturn's axis causes the sun to heat
the planet's northern and southern halves
unequally, resulting in seasons and temperature
changes. Each season lasts about 7 1/2 Earth
years, because Saturn takes about 29 times as
long to go around the sun as Earth does. Saturn's
temperature is always much colder than Earth's,
because Saturn is so far from the sun. The
temperature at the top of Saturn's clouds
averages -285 degrees F (-175 degrees C).
The temperatures below Saturn's clouds are
much higher than those at the top of the clouds.
The planet gives off about 2 1/2 times as much
heat as it receives from the sun. Many
astronomers believe that much of Saturn's
internal heat comes from energy generated by
the sinking of helium slowly through the liquid
hydrogen in the planet's interior.
Density and mass
Saturn has a lower density than any other planet.
It is only about one-tenth as dense as Earth, and
about two-thirds as dense as water. That is, a
portion of Saturn would weigh much less than
an equal portion of Earth, and would float in
water.
Although Saturn has a low density, it has a
greater mass than any other planet except
Jupiter. Saturn is about 95 times as massive as
Earth. The force of gravity is a little higher on
Saturn than on Earth. A 100-pound object on
Earth would weigh about 107 pounds on Saturn.
Rings
The rings of Saturn surround the planet at its
equator. They do not touch Saturn. As Saturn
orbits the sun, the rings always tilt at the same
angle as the equator.
The seven rings of Saturn consist of thousands
of narrow ringlets. The ringlets are made up of
billions of pieces of ice. These pieces range from
ice particles that are the size of dust to chunks of
ice that measure more than 10 feet (3 meters) in
diameter.
Saturn's major rings are extremely wide. The
outermost ring, for example, may measure as
much as 180,000 miles (300,000 kilometers)
across. However, the rings of Saturn are so thin
that they cannot be seen when they are in direct
line with Earth. They vary in thickness from
about 660 to 9,800 feet (200 to 3,000 meters). A
space separates the rings from one another. Each
of these gaps is about 2,000 miles (3,200
kilometers) or more in width. However, some of
the gaps between the major rings contain
ringlets.
Saturn's rings
were
discovered in
the early
1600's by the
Italian
astronomer
Galileo.
Galileo could
not see the
rings clearly
with his small
telescope, and The dark side of Saturn's rings
thought they was photographed by Voyager 1
as it flew by the side opposite the
were large
satellites. In sun. The dense B-ring -- the
reddish-brown band -- appears
1656, after
using a more dark because it blocks much of
the sunlight. It is the brightest
powerful
ring when viewed from earth.
telescope,
Image credit: JPL
Christiaan
Huygens, a Dutch astronomer, described a "thin,
flat" ring around Saturn. Huygens thought the
ring was a solid sheet of some material. In 1675,
Giovanni Domenico Cassini, an Italian-born
French astronomer, announced the discovery of
two separate rings made up of swarms of
satellites. Later observations of Saturn resulted
in the discovery of more rings. The ringlets were
discovered in 1980.
Satellites
In addition to its rings, Saturn has 25 satellites
that measure at least 6 miles (10 kilometers) in
diameter, and several smaller satellites. The
largest of Saturn's satellites, Titan, has a
diameter of about 3,200 miles (5,150 kilometers)
-- larger than the planets Mercury and Pluto.
Titan is one of the few satellites in the solar
system known to have an atmosphere. Its
atmosphere consists largely of nitrogen.
Many of Saturn's satellites have large craters.
For example, Mimas has a crater that covers
about one-third the diameter of the satellite.
Another satellite, Iapetus, has a bright side and a
dark side. The bright side of this satellite reflects
about 10 times as much sunlight as the dark side.
The satellite Hyperion is shaped somewhat like a
squat cylinder rather than like a sphere. Unlike
Saturn's other satellites, Hyperion's axis does not
point toward the planet.
Flights to Saturn
In 1973, the United States launched a space
probe to study both Saturn and Jupiter. This
craft, called Pioneer-Saturn, sped by Jupiter in
1974 and flew within 13,000 miles (20,900
kilometers) of Saturn on Sept. 1, 1979. The
probe sent back scientific data and close-up
photographs of Saturn. The data and
photographs led to the discovery of two of the
planet's outer rings.
Pioneer-Saturn also found that the planet has a
magnetic field, which is 1,000 times as strong as
that of Earth. This field produces a large
magnetosphere (zone of strong magnetic forces)
around Saturn. In addition, data from the probe
indicated the presence of radiation belts inside
the planet's magnetosphere. The belts consist of
high-energy electrons and protons, and are
comparable to Earth's Van Allen belts.
In 1977, the
United States
launched two
space probes - Voyager 1
and Voyager
2 -- to study
Saturn and
other planets.
Voyager 1
flew within
78,000 miles
(126,000
kilometers) of
The Cassini probe, launched in
Saturn on
1997, began orbiting Saturn in
Nov. 12,
2004. Cassini was designed to
1980. On
study Saturn, its rings, and its
Aug. 25,
moons and to drop a probe called
1981,
Huygens into the atmosphere of
Voyager 2
flew within the moon Titan. Image credit:
63,000 miles NASA
(101,000 kilometers) of the planet.
The Voyager probes confirmed the existence of
Saturn's seventh ring. They also found that the
planet's rings are made up of ringlets. In
addition, the probes sent back data and
photographs that led to the discovery or
confirmation of the existence of nine satellites.
The Voyager probes also determined that the
atmosphere of Titan consists chiefly of nitrogen.
In 1997, the United States launched the Cassini
probe to study Saturn, its rings, and its satellites.
The probe began orbiting Saturn in 2004.
Cassini also carried a probe called Huygens,
which was to separate from Cassini and land on
Titan. Huygens was built by the European Space
Agency, an organization of European nations.
Contributor: Hyron Spinrad, Ph.D., Professor of
Astronomy, University of California, Berkeley.
Spinrad, Hyron. "Saturn." World Book Online
Reference Center. 2004. World Book, Inc.
http://www.worldbookonline.com/wb/Article?id
=ar492440.
USA Today
Feb 11, 2010
Hubble catches Saturn's
sky shows from space
Northern and Southern Lights on Saturn's poles,
seen by the Hubble telescope.
NASA astronomers Thursday released movies
of Saturn's northern and southern lights, seen
edge-on. The ringed planet moves into its
equinox, where both poles are equally
illuminated by the sun and viewable from Earth,
only every 15 years, allowing for Hubble's
unique vantage on the planet's aurorae.
"Given the rarity of such an event, this new
footage will likely be the last and best equinox
movie that Hubble captures of our planetary
neighbour," says a European Space Agency
statement. Aurorae result from charged solar
wind particles trapped in a planet's magnetic
field striking atoms in the upper atmosphere.
Just like Northern Lights on Earth, Saturn sees
similar polar light shows as a result.
Saturn's northern and southern aurorae differ,
the astronomers report. The northern magnetic
field appears more intense, suggesting Saturn's
magnetic field is not distributed evenly around
the planet. The finding supports measurements
made by the international Cassini spacecraft,
which has orbited Saturn since 2004 and
recently had its exploration mission extended.
By Dan Vergano