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Jupiter

2007 Schools Wikipedia Selection. Related subjects: The Planets

   CAPTION: Jupiter Astronomical symbol of Jupiter

               Click for full caption.
   Click image for description
       Orbital characteristics ( Epoch J2000)
   Semi-major axis       778,412,027 km
                         5.203 363 01 AU
   Orbital circumference 4.888 T m
                         32.675 AU
   Eccentricity          0.048 392 66
   Perihelion            740,742,598 km
                         4.951 558 43 AU
   Aphelion              816,081,455 km
                         5.455 167 59 AU
   Orbital period        4333.2867 d
                         (11.86 a)
   Synodic period        398.88 d
   Avg. Orbital Speed    13.056 km/s
   Max. Orbital Speed    13.712 km/s
   Min. Orbital Speed    12.446 km/s
   Inclination           1.305 30°
                         (6.09° to Sun's equator)
   Longitude of the
   ascending node        100.556 15°
   Argument of the
   perihelion            274.197 70°
   Number of satellites  63
              Physical characteristics
   Equatorial diameter   142,984 km
                         (11.209 Earths)
   Polar diameter        133,709 km
                         (10.517 Earths)
   Oblateness            0.064 87
   Surface area          6.14×10^10 km^2
                         (120.5 Earths)
   Volume                1.431×10^15 km^3
                         (1321.3 Earths)
   Mass                  1.899×10^27 kg
                         (317.8 Earths)
   Mean density          1.326 g/cm^3
   Equatorial gravity    23.12 m/s^2
                         (2.358 gee)
   Escape velocity       59.54 km/s
   Rotation period       0.413 538 021 d
                         (9 h 55 min 29.685 s)
   Rotation velocity     12.6 km/s = 45,300 km/h
                         (at the equator)
   Axial tilt            3.13°
   Right ascension
   of North pole         268.05° (17 h 52 min 12 s)
   Declination           64.49°
   Albedo                0.52
   Surface temp.
                          min  mean   max
                         110 K 152 K N/A K
   Adjective             Jovian
             Atmospheric characteristics
   Atmospheric pressure  70 kPa
   Hydrogen              ~86%
   Helium                ~14%
   Methane               0.1%
   Water vapor           0.1%
   Ammonia               0.02%
   Ethane                0.0002%
   Phosphine             0.0001%
   Hydrogen sulfide      <0.00010%

   Jupiter ( IPA: /dʒu'pItɺ/) is the fifth planet from the Sun and the
   largest within the solar system. Jupiter and the other gas
   giants—Saturn, Uranus, and Neptune—are sometimes referred to as "
   Jovian planets".

Overview

   Jupiter is usually the fourth brightest object in the sky (after the
   Sun, the Moon and Venus); however at times Mars appears brighter than
   Jupiter.
   Approximate size comparison of Earth and Jupiter, including the Great
   Red Spot
   Enlarge
   Approximate size comparison of Earth and Jupiter, including the Great
   Red Spot

   Jupiter is 2.5 times more massive than all the other planets combined,
   so massive that its barycenter with the Sun actually lies above the
   Sun's surface (1.068 solar radii from the Sun's centre). It is 318
   times more massive than Earth, with a diameter 11 times that of Earth,
   and its volume is 1300 times as great as that of Earth. Quite
   naturally, Jupiter's gravitational influence has dominated the
   evolution of the solar system: some have described the solar system as
   consisting of the Sun, Jupiter, and assorted debris. Most planets'
   orbits lie closer to Jupiter's orbital plane than the Sun's equatorial
   plane (Mercury is the only planet which is closer to the Sun's equator
   in orbital tilt), the majority of short-period comets belong to
   Jupiter's family (a result due to both Jupiter's mass and its relative
   speed), the Kirkwood gaps in the asteroid belt are mostly due to
   Jupiter, and the planet may have been responsible for the Late Heavy
   Bombardment of the inner solar system's history. Jupiter has been
   called the solar system's vacuum cleaner, due to its immense gravity
   well.

   As impressive as Jupiter's mass is, extrasolar planets have been
   discovered with much greater masses. There is no clear-cut definition
   of what distinguishes a large planet such as Jupiter from a brown dwarf
   star, although the latter possesses rather specific spectral lines.
   Currently, if an object of solar metallicity is 13 Jupiter masses or
   above, large enough to burn deuterium, it is considered a brown dwarf;
   below that mass (and orbiting a star or stellar remnant), it is a
   planet. Jupiter is thought to have about as large a diameter as a
   planet of its composition can; adding extra mass would result in
   further gravitational compression, in theory leading to stellar
   ignition. This has led some astronomers to term it a "failed star" --
   although Jupiter would need to be about seventy-five times as massive
   to become a star, the smallest red dwarf is only about 30% larger than
   Jupiter. In light of this, it is also interesting to note that it
   radiates more heat than it receives from the Sun. This additional heat
   radiation is produced by the Kelvin-Helmholtz mechanism. As another
   symptom of this process, the planet shrinks at the rate of a few
   millimeters each year. When it was younger and hotter, Jupiter was much
   larger than it is today, though previously Saturn would have been even
   bigger than Jupiter due to its lower mass: Saturn has a much weaker
   gravitational pull and with more heat, both planets would have been
   more bloated (and because of Saturn's lower core mass, this effect
   would have been greater). In general, the more massive the core, the
   smaller the planet in size.
   Aurora borealis on Jupiter.
   Enlarge
   Aurora borealis on Jupiter.

   Jupiter also has the fastest rotation rate of any planet within the
   solar system, making a complete rotation on its axis in slightly less
   than ten hours, which results in an equatorial bulge easily seen
   through an Earth-based amateur telescope. Jupiter is perpetually
   covered with a layer of clouds, composed of ammonia crystals and
   possibly ammonium hydrosulphide, and it may not have any solid surface
   in that the density may simply increase gradually as you move towards
   the core. Its best known feature is the Great Red Spot, a storm larger
   than Earth which was likely first observed by Giovanni Domenico Cassini
   and Robert Hooke four centuries ago. Indeed, mathematical models
   suggest that the storm is stable and may be a permanent feature of the
   planet. In 2000, three small spots merged to form a larger spot named
   Oval BA, which later acquired a red hue very similar to that of the
   Great Red Spot.

Historical observations

   The planet Jupiter has been known since ancient times and is visible to
   the naked eye in the night sky. The Romans named the planet after the
   Roman god Jupiter (also called Jove). The astronomical symbol for the
   planet is a stylized representation of the god's lightning bolt. ♃ is
   found at Unicode position U+2643.

   The Chinese, Korean, Japanese, and Vietnamese refer to the planet as
   the wood star, 木星, based on the Chinese Five Elements. In Vedic
   Astrology, Hindu astrologers refer to Jupiter as Brihaspati, or "Guru"
   which means the "Big One". In Hindi, Thursday is referred to as
   Guruvaar (day of Jupiter). In the English language Thursday is rendered
   as Thor's day, with Thor being identified with the Roman god Jupiter.

   In 1610, Galileo Galilei discovered the four largest moons of Jupiter,
   Io, Europa, Ganymede and Callisto (now known as the Galilean moons)
   using a telescope, the first observation of moons other than Earth's.
   This was also the first discovery of a celestial motion not apparently
   centered on the Earth. It was a major point in favour of Copernicus'
   heliocentric theory of the motions of the planets; Galileo's outspoken
   support of the Copernican theory placed him under the threat of the
   Inquisition.

   In 1892, E. E. Barnard observed a fifth satellite of Jupiter with the
   36-inch refractor at Lick Observatory in California. The discovery, a
   testament to his extraordinary eyesight, made him quickly famous. The
   moon was later named Amalthea.

Physical characteristics

Planetary composition

   Jupiter is composed of a relatively small rocky core, surrounded by
   metallic hydrogen, with further layers of liquid hydrogen and gaseous
   hydrogen. There is no clear boundary or surface between these different
   phases of hydrogen; the conditions blend smoothly from gas to liquid as
   one descends.

Atmosphere

   False-color detail of Jupiter's atmosphere, imaged by Voyager 1,
   showing the Great Red Spot and a passing white oval
   Enlarge
   False-colour detail of Jupiter's atmosphere, imaged by Voyager 1,
   showing the Great Red Spot and a passing white oval

   Jupiter's atmosphere is composed of ~90% hydrogen and ~10% helium by
   number of atoms. The atmosphere is ~75%/24% by mass; with ~1% of the
   mass accounted for by other substances - the interior contains denser
   materials such that the distribution is ~71%/24%/5%. The atmosphere
   contains trace amounts of methane, water vapor, ammonia, and "rock".
   There are also traces of carbon, ethane, hydrogen sulphide, neon,
   oxygen, phosphine, and sulphur. The outermost layer of the atmosphere
   contains crystals of frozen ammonia. Through IR and UV measurements
   benzene (at a relative mixing ratio of 2x10^-9 to hydrogen) and other
   hydrocarbons have also been found.

   This atmospheric composition is very close to the composition of the
   solar nebula. Saturn has a similar composition, but Uranus and Neptune
   have much less hydrogen and helium.

   Jupiter's upper atmosphere undergoes differential rotation, an effect
   first noticed by Giovanni Cassini ( 1690). The rotation of Jupiter's
   polar atmosphere is ~5 minutes longer than that of the equatorial
   atmosphere. In addition, bands of clouds of different latitudes, known
   as tropical regions flow in opposing directions on the prevailing
   winds. The interactions of these conflicting circulation patterns cause
   storms and turbulence. Wind speeds of 600 km/h are not uncommon.

   The only spacecraft to have descended into Jupiter's atmosphere to take
   scientific measurements is the Galileo probe (see Galileo mission). It
   sent an atmospheric probe into Jupiter upon arrival in 1995, then
   itself entered Jupiter's atmosphere and burned up in 2003.

The Great Red Spot

                        The Great Red Spot as seen from Voyager 1 in 1979.
                                                                   Enlarge
                        The Great Red Spot as seen from Voyager 1 in 1979.

                                Color animation of Jupiter's cloud motion.
                                                                   Enlarge
                               Colour animation of Jupiter's cloud motion.

                                        An animation of the Great Red Spot
                                                                   Enlarge
                                        An animation of the Great Red Spot

   Image of Jupiter by Pioneer 10 in 1974. The Great Red Spot appears more
    prominent here than in the Voyager images because of its location in a
                                           lighter colored band of clouds.
                                                                   Enlarge
   Image of Jupiter by Pioneer 10 in 1974. The Great Red Spot appears more
    prominent here than in the Voyager images because of its location in a
                                           lighter colored band of clouds.

   The Great Red Spot is a persistent anticyclonic storm on the planet
   Jupiter, 22° south of the equator, which has lasted at least 340 years.
   The storm is large enough to be visible through Earth-based telescopes.
   It was probably first observed by Giovanni Domenico Cassini, who
   described it around 1665.

   This dramatic view of Jupiter's Great Red Spot and its surroundings was
   obtained by Voyager 1 on February 25, 1979, when the spacecraft was 9.2
   million km (5.7 million miles) from Jupiter. Cloud details as small as
   160 km (100 miles) across can be seen here. The colorful, wavy cloud
   pattern to the left of the Red Spot is a region of extraordinarily
   complex and variable wave motion. To give a sense of Jupiter's scale,
   the white oval storm directly below the Great Red Spot is approximately
   the same diameter as Earth.

   The oval object rotates counterclockwise, with a period of about 6
   days. The Great Red Spot's dimensions are 24–40,000 km × 12–14,000 km.
   It is large enough to contain two or three planets of Earth size. The
   cloudtops of this storm are about 8 km above the surrounding cloudtops.

   Storms such as this are not uncommon within the turbulent atmospheres
   of gas giants. Jupiter also has white ovals and brown ovals, which are
   lesser unnamed storms. White ovals tend to consist of relatively cool
   clouds within the upper atmosphere. Brown ovals are warmer and located
   within the "normal cloud layer". Such storms can last hours or
   centuries.

   Before the Voyager missions, astronomers were highly uncertain of its
   nature. Many believed it to be a solid or liquid feature on Jupiter's
   surface.

Planetary rings

   Enlarge

   Jupiter has a faint planetary ring system composed of smoke-like dust
   particles knocked from its moons by energetic meteor impacts. The
   innermost doughnut-shaped ring, called the halo, is almost as thick
   (20,000km) as it is wide (22,800km). This is followed by the thinnest
   and brightest main ring, which is made of dust from the satellites
   Adrastea and Metis. Metis orbits within its fluid Roche limit with
   Jupiter, and objects not rigidly attached to it may freely fall away
   from it and into Jupiter's gravitational field. Two wide gossamer rings
   encircle the main ring, originating from Thebe and Amalthea. Finally,
   there is a distant and very faint outer ring circling Jupiter
   backwards—retrograde of its spin. It is not known for certain where the
   material for this outer ring comes from, but it may be captured
   interplanetary dust.

Magnetosphere

   Jupiter has a very large and powerful magnetosphere. In fact, if one
   could see Jupiter's magnetic field from Earth, it would appear five
   times as large as the full moon in the sky despite being so much
   farther away. The magnetic field is generated by eddy currents in
   Jupiter's metallic hydrogen core. This magnetic field collects a large
   flux of particle radiation in Jupiter's radiation belts, as well as
   producing a dramatic gas torus and flux tube associated with Io(one of
   Jupiter's moon). Jupiter's magnetosphere is the largest planetary
   structure in the solar system.

   The Pioneer probes confirmed that Jupiter's enormous magnetic field is
   10 times stronger than Earth's and contains 20,000 times as much
   energy. The sensitive instruments aboard found that the Jovian magnetic
   field's "north" magnetic pole is at the planet’s geographic south pole,
   with the axis of the magnetic field tilted 11 degrees from the Jovian
   rotation axis and offset from the centre of Jupiter in a manner similar
   to the axis of the Earth's field. The Pioneers measured the bow shock
   of the Jovian magnetosphere to the width of 26 million kilometers (16
   million miles), with the magnetic tail extending beyond Saturn’s orbit.

   The data showed that the magnetic field fluctuates rapidly in size on
   the sunward side of Jupiter because of pressure variations in the solar
   wind, an effect studied in further detail by the two Voyager
   spacecraft. It was also discovered that streams of high-energy atomic
   particles are ejected from the Jovian magnetosphere and travel as far
   as the orbit of the Earth. Energetic protons were found and measured in
   the Jovian radiation belt and electric currents were detected flowing
   between Jupiter and some of its moons, particularly Io.

Exploration of Jupiter

   A number of probes have visited Jupiter.

Pioneer flyby missions

   Pioneer 10 flew past Jupiter in December of 1973, followed by Pioneer
   11 exactly one year later. Pioneer 10 obtained the first ever close up
   images of Jupiter and the Galilean moons, studied its atmosphere,
   detected its magnetic field, observed its radiation belts and found
   that Jupiter is mainly liquid.

Voyager flyby missions

   Voyager 1 took this photo of the planet Jupiter on January 24, 1979
   while still more than 25 million miles (40 million kilometres) away.
   Click image for full caption.
   Enlarge
   Voyager 1 took this photo of the planet Jupiter on January 24, 1979
   while still more than 25 million miles (40 million kilometres) away.
   Click image for full caption.

   Voyager 1 flew by in March 1979 followed by Voyager 2 in July of the
   same year. The Voyagers vastly improved the understanding of the
   Galilean moons and discovered Jupiter's rings. They also took the first
   close up images of the planet's atmosphere.

Ulysses flyby mission

   In February 1992, Ulysses solar probe performed a flyby of Jupiter at a
   distance of 450,000 km (6.3 Jovian radii). The flyby was required to
   attain a polar orbit around the Sun. The probe conducted studies on
   Jupiter's magnetosphere. Since there are no cameras onboard the probe,
   no images were taken. In February 2004, the probe came again in the
   vicinity of Jupiter. This time the distance was much greater, about 240
   million km.

Galileo mission

   So far the only spacecraft to orbit Jupiter is the Galileo orbiter,
   which went into orbit around Jupiter on December 7, 1995. It orbited
   the planet for over seven years and conducted multiple flybys of all of
   the Galilean moons and Amalthea. The spacecraft also witnessed the
   impact of Comet Shoemaker-Levy 9 into Jupiter as it approached the
   planet in 1994, giving a unique vantage point for this spectacular
   event. However, while the information gained about the Jovian system
   from the Galileo mission was extensive in its own right, its
   originally-designed capacity was limited by the failed deployment of
   its high-gain radio transmitting antenna.
   Jupiter as seen by the space probe Cassini. This is the most detailed
   global color portrait of Jupiter ever assembled.
   Enlarge
   Jupiter as seen by the space probe Cassini. This is the most detailed
   global colour portrait of Jupiter ever assembled.

   An atmospheric probe was released from the spacecraft in July 1995. The
   probe entered the planet's atmosphere on December 7, 1995. It
   parachuted through 150 km of the atmosphere, collecting data for 57.6
   minutes, before being crushed by the extreme pressure to which it was
   subjected. It would have melted and vaporized shortly thereafter. The
   Galileo orbiter itself experienced a more rapid version of the same
   fate when it was deliberately steered into the planet on September 21,
   2003 at a speed of over 50 km/s, in order to avoid any possibility of
   it crashing into and possibly contaminating Europa, one of the Jovian
   moons.

Cassini flyby mission

   In 2000, the Cassini probe, en route to Saturn, flew by Jupiter and
   provided some of the highest-resolution images ever made of the planet.
   On December 19, 2000, the Cassini spacecraft, captured a very low
   resolution image of the moon Himalia, but it was too distant to show
   any surface details.

New Horizons flyby mission

   The New Horizons probe and its Atlas V launcher lifted off from Pad 41
   at Cape Canaveral Air Force Station, Florida, directly south of Space
   Shuttle Launch Complex 39, at 2:00 p.m. EST (1900 UTC) on January 19,
   2006. New Horizons passed Lunar orbit before midnight EST on the same
   day, and is scheduled to reach Jupiter in February 2007. It will pass
   through the Jupiter system at 21 km/s (47,000 mph), with closest
   approach to Jupiter occurring at approximately 06:00 UTC February 28,
   2007.

   The flyby will come within about 32 Jovian radii (3 Gm) of Jupiter and
   will be the centre of a 4-month intensive observation campaign. New
   Horizons also has instruments built twenty years after Galileo's -
   particularly Galileo's cameras, which were evolved versions of Voyager
   cameras which, in turn, were evolved Mariner cameras. Because of the
   much shorter distance from Jupiter to Earth, the communications link
   can transmit multiple loadings of the memory buffer. The mission will
   actually return more data from Jupiter than Pluto. Imaging of Jupiter
   began on September 4, 2006.

Future probes

   NASA is planning a mission to study Jupiter in detail from a polar
   orbit. Named Juno, the spacecraft is planned to launch by 2010.

   Because of the possibility of a liquid ocean on Jupiter's moon Europa,
   there has been great interest to study the icy moons in detail. A
   mission proposed by NASA was dedicated to study them. The JIMO (Jupiter
   Icy Moons Orbiter) was expected to be launched sometime after 2012.
   However, the mission was deemed too ambitious and its funding was
   cancelled.

Natural satellites

   Jupiter's 4 Galilean moons, in a composite image comparing their sizes
   and the size of Jupiter (Great Red Spot visible). From the top they
   are: Callisto, Ganymede, Europa and Io.
   Enlarge
   Jupiter's 4 Galilean moons, in a composite image comparing their sizes
   and the size of Jupiter (Great Red Spot visible). From the top they
   are: Callisto, Ganymede, Europa and Io.

   Jupiter has at least 63 moons. For a complete listing of these moons,
   please see Jupiter's natural satellites. For a timeline of their
   discovery dates, see Timeline of discovery of Solar System planets and
   their natural satellites.

   The four large moons, known as the " Galilean moons", are Io, Europa,
   Ganymede and Callisto.

Galilean moons

   The orbits of Io, Europa, and Ganymede, the largest moon in the solar
   system, form a pattern known as a Laplace resonance; for every four
   orbits that Io makes around Jupiter, Europa makes exactly two orbits
   and Ganymede makes exactly one. This resonance causes the gravitational
   effects of the three moons to distort their orbits into elliptical
   shapes, since each moon receives an extra tug from its neighbors at the
   same point in every orbit it makes.
   A picture of Jupiter and its moon Io taken by Hubble. The black spot is
   Io's shadow.
   Enlarge
   A picture of Jupiter and its moon Io taken by Hubble. The black spot is
   Io's shadow.

   The tidal force from Jupiter, on the other hand, works to circularize
   their orbits. This constant tug of war causes regular flexing of the
   three moons' shapes, Jupiter's gravity stretches the moons more
   strongly during the portion of their orbits that are closest to it and
   allowing them to spring back to more spherical shapes when they're
   farther away. This flexing causes tidal heating of the three moons'
   cores. This is seen most dramatically in Io's extraordinary volcanic
   activity, and to a somewhat less dramatic extent in the geologically
   young surface of Europa indicating recent resurfacing.
   The Galilean moons, compared to Earth's moon Luna
   Name

   ( Pronunciation key)
   Diameter
   (km) Mass
   (kg) Orbital radius (km) Orbital period (days)
                                 Io eye'-oe
                               ˈaɪəʊ 3643
                           (105% Luna) 8.9×10^22
                             (120% Luna) 421 700
                              (110% Luna) 1.77
                                 (6.5% Luna)
                             Europa ew-roe'-pə
                             jʊˈrəʊpə 3122
                            (90% Luna) 4.8×10^22
                             (65% Luna) 671 034
                              (175% Luna) 3.55
                                 (13% Luna)
                            Ganymede gan'-ə-meed
                              ˈgænəmid 5262
                           (150% Luna) 14.8×10^22
                            (200% Luna) 1 070 412
                              (280% Luna) 7.15
                                 (26% Luna)
                            Callisto kə-lis'-toe
                             kəˈlɪstəʊ 4821
                           (140% Luna) 10.8×10^22
                            (150% Luna) 1 882 709
                              (490% Luna) 16.69
                                 (61% Luna)

Classification of Jupiter's moons

   Before the discoveries of the Voyager missions, Jupiter's moons were
   arranged neatly into four groups of four. Since then, the large number
   of new small outer moons has complicated this picture. There are now
   thought to be six main groups, although some are more distinct than
   others. A basic division is between the eight inner regular moons with
   nearly circular orbits near the plane of Jupiter's equator, which are
   believed to have formed with Jupiter, and an unknown number of small
   irregular moons, with elliptical and inclined orbits, which are
   believed to be captured asteroids or fragments of captured asteroids.
   Europa, one of Jupiter's many moons.
   Enlarge
   Europa, one of Jupiter's many moons.
    1. Regular moons
         1. The inner group of four small moons all have diameters of less
            than 200 km, orbit at radii less than 200,000 km, and have
            orbital inclinations of less than half a degree..
         2. The four Galilean moons, discovered by Galileo Galilei and by
            Simon Marius in parallel, orbit between 400,000 and 2,000,000
            km, and include some of the largest moons in the solar system.
    2. Irregular moons
         1. Themisto is in a group of its own, orbiting halfway between
            the Galilean moons and the next group.
         2. The Himalia group is a tightly clustered group of moons with
            orbits around 11,000,000-12,000,000 km from Jupiter.
         3. Carpo is another isolated case; at the inner edge of the
            Ananke group, it revolves in the direct sense.
         4. The Ananke group is a group with rather indistinct borders,
            averaging 21,276,000 km from Jupiter with an average
            inclination of 149 degrees.
         5. The Carme group is a fairly distinct group that averages
            23,404,000 km from Jupiter with an average inclination of 165
            degrees.
         6. The Pasiphaë group is a dispersed and only vaguely distinct
            group that covers all the outermost moons.

   It is thought that the groups of outer moons may each have a common
   origin, perhaps as a larger moon or captured body that broke up.

Life on Jupiter

   It is considered highly unlikely that there is any Earth-like life on
   Jupiter, as there is little water in the atmosphere and any possible
   solid surface deep within Jupiter would be under extraordinary
   pressures. However, in 1976, before the Voyager missions, Carl Sagan
   hypothesized (with Edwin Ernest Salpeter) that ammonia-based life could
   evolve in Jupiter's upper atmosphere. Sagan and Salpeter based this
   hypothesis on the ecology of terrestrial seas which have simple
   photosynthetic plankton at the top level, fish at lower levels feeding
   on these creatures, and marine predators which hunt the fish. The
   Jovian equivalents Sagan and Salpeter hypothesized were "sinkers",
   "floaters", and "hunters". The "sinkers" would be plankton-like
   organisms which fall through the atmosphere, existing just long enough
   that they can reproduce in the time they are kept afloat by convection.
   The "floaters" would be giant bags of gas functioning along the lines
   of hot air balloons, using their own metabolism (feeding off sunlight
   and free molecules) to keep their gas warm. The "hunters" would be
   almost squid-like creatures, using jets of gas to propel themselves
   into "floaters" and consume them.
   This diagram shows the Trojan Asteroids in Jupiter's orbit, as well as
   the main asteroid belt
   Enlarge
   This diagram shows the Trojan Asteroids in Jupiter's orbit, as well as
   the main asteroid belt

Trojan asteroids

   In addition to its moons, Jupiter's gravitational field controls
   numerous asteroids which have settled into the regions of the
   Lagrangian points preceding and following Jupiter in its orbit around
   the sun. These are known as the Trojan asteroids, and are divided into
   Greek and Trojan "camps" to commemorate the Iliad. The first of these,
   588 Achilles, was discovered by Max Wolf in 1906; since then hundreds
   more have been discovered. The largest is 624 Hektor.

Cometary impact

   Aftermath of impact of a cometary fragment. The dark scars visible on
   the cloudtops were larger than Earth itself.
   Enlarge
   Aftermath of impact of a cometary fragment. The dark scars visible on
   the cloudtops were larger than Earth itself.

   During the period July 16 to July 22, 1994, over twenty fragments from
   the comet Shoemaker-Levy 9 hit Jupiter's southern hemisphere, providing
   the first direct observation of a collision between two solar system
   objects. It is thought that due to Jupiter's large mass and location
   near the inner solar system it receives the most frequent comet impacts
   of the solar system's planets.

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