From Wikipedia, the free encyclopedia
Jupiter 
Full-disc view of Jupiter in natural color in April 2014
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| Designations |
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| Pronunciation | |
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| Adjectives | Jovian |
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| Orbital characteristics |
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| Epoch J2000 |
| Aphelion | 816.62 million km (5.4588 AU) |
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| Perihelion | 740.52 million km (4.9501 AU) |
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|
| 778.57 million km (5.2044 AU) |
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| Eccentricity | 0.0489 |
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|
|
|
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|
| 398.88 d |
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|
| 13.07 km/s (8.12 mi/s) |
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|
| 20.020° |
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| Inclination |
|
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|
| 100.464° |
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|
| 273.867° |
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| Known satellites | 79 (as of 2018) |
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| Physical characteristics |
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Mean radius
| 69,911 km (43,441 mi) |
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|
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- 71,492 km (44,423 mi)
- 11.209 Earths
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|
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- 66,854 km (41,541 mi)
- 10.517 Earths
|
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| Flattening | 0.06487 |
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- 6.1419×1010 km2 (2.3714×1010 sq mi)
- 121.9 Earths
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| Volume |
- 1.4313×1015 km3 (3.434×1014 cu mi)
- 1,321 Earths
|
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| Mass |
- 1.8982×1027 kg (4.1848×1027 lb)
- 317.8 Earths
- 1/1047 Sun
|
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|
| 1,326 kg/m3 (2,235 lb/cu yd) |
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|
| 24.79 m/s2 (81.3 ft/s2)
2.528 g |
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|
| 0.254 I/MR2 (estimate) |
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| 59.5 km/s (37.0 mi/s) |
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|
| 9.925 hours (9 h 55 m 30 s) |
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Equatorial rotation velocity
| 12.6 km/s (7.8 mi/s; 45,000 km/h) |
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|
| 3.13° (to orbit) |
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|
| 268.057°; 17h 52m 14s |
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|
| 64.495° |
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| Albedo | 0.503 (Bond)
0.538 (geometric) |
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| Surface temp. |
min |
mean |
max |
| 1 bar level |
|
165 K (−108 °C) |
|
| 0.1 bar |
|
112 K (−161 °C) |
|
|
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| −2.94 to −1.66 |
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|
| 29.8″ to 50.1″ |
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| Atmosphere |
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|
| 20–200 kPa; 70 kPa |
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|
| 27 km (17 mi) |
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| Composition by volume | by volume:
Ices:
|
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Jupiter is the fifth
planet from the
Sun and the
largest in the
Solar System. It is a
giant planet with a
mass
one-thousandth that of the Sun, but two-and-a-half times that of all
the other planets in the Solar System combined. Jupiter and
Saturn are
gas giants; the other two giant planets,
Uranus and
Neptune, are
ice giants. Jupiter has been known to
astronomers since antiquity. It is named after the
Roman god Jupiter. When viewed from
Earth, Jupiter can reach an
apparent magnitude of −2.94, bright enough for its
reflected light to cast shadows, and making it on average the third-brightest natural object in the
night sky after the
Moon and
Venus.
Jupiter is primarily composed of
hydrogen with a quarter of its mass being
helium, though helium comprises only about a tenth of the number of molecules. It may also have a rocky core of heavier elements,
but like the other giant planets, Jupiter lacks a well-defined solid
surface. Because of its rapid rotation, the planet's shape is that of an
oblate spheroid
(it has a slight but noticeable bulge around the equator). The outer
atmosphere is visibly segregated into several bands at different
latitudes, resulting in turbulence and storms along their interacting
boundaries. A prominent result is the
Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by
telescope. Surrounding Jupiter is a faint
planetary ring system and a powerful
magnetosphere. Jupiter has
79 known moons, including the four large
Galilean moons discovered by
Galileo Galilei in 1610.
Ganymede, the largest of these, has a diameter greater than that of the planet
Mercury.
Jupiter has been explored on several occasions by
robotic spacecraft, most notably during the early
Pioneer and
Voyager flyby missions and later by the
Galileo orbiter. In late February 2007, Jupiter was visited by the
New Horizons probe, which
used Jupiter's gravity to increase its speed and bend its trajectory en route to
Pluto. The latest probe to visit the planet is
Juno, which entered into orbit around Jupiter on July 4, 2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon
Europa.
Formation and migration
Astronomers have discovered nearly 500 planetary systems with
multiple planets. Regularly these systems include a few planets with
masses several times greater than Earth's (
super-Earths), orbiting closer to their star than Mercury is to the Sun, and sometimes also Jupiter-mass gas giants close to their star.
Earth and its neighbor planets may have formed from fragments of
planets after collisions with Jupiter destroyed those super-Earths near
the Sun. As Jupiter came toward the inner Solar System, in what
theorists call the
grand tack hypothesis,
gravitational tugs and pulls occurred causing a series of collisions
between the super-Earths as their orbits began to overlap.
Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including
Earth.
Physical characteristics
Jupiter is composed primarily of gaseous and liquid matter. It is the
largest of the four giant planets in the Solar System and hence its
largest planet. It has a diameter of 142,984 km (88,846 mi) at its
equator. The average density of Jupiter, 1.326 g/cm
3, is the second highest of the giant planets, but lower than those of the four
terrestrial planets.
Composition
Jupiter's upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas
molecules.
A helium atom has about four times as much mass as a hydrogen atom, so
the composition changes when described as the proportion of mass
contributed by different atoms. Thus,
Jupiter's atmosphere
is approximately 75% hydrogen and 24% helium by mass, with the
remaining one percent of the mass consisting of other elements. The
atmosphere contains trace amounts of
methane,
water vapor,
ammonia, and
silicon-based compounds. There are also traces of
carbon,
ethane,
hydrogen sulfide,
neon,
oxygen,
phosphine, and
sulfur. The outermost layer of the atmosphere contains
crystals
of frozen ammonia. The interior contains denser materials - by mass it
is roughly 71% hydrogen, 24% helium, and 5% other elements. Through
infrared and
ultraviolet measurements, trace amounts of
benzene and other
hydrocarbons have also been found.
The atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial
solar nebula. Neon in the upper atmosphere only consists of 20 parts per million by mass, which is about a tenth as abundant as in the Sun. Helium is also depleted to about 80% of the Sun's helium composition. This depletion is a result of
precipitation of these elements into the interior of the planet.
Based on
spectroscopy,
Saturn is thought to be similar in composition to Jupiter, but the other giant planets
Uranus and
Neptune have relatively less hydrogen and helium and relatively more
ices and are thus now termed
ice giants.
Mass and size
Jupiter's diameter is one order of magnitude
smaller (×0.10045) than that of the Sun, and one order of magnitude
larger (×10.9733) than that of Earth. The Great Red Spot is roughly the
same size as Earth.
Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its
barycenter with the
Sun lies above the
Sun's surface at 1.068
solar radii from the Sun's center.
Jupiter is much larger than Earth and considerably less dense: its
volume is that of about 1,321 Earths, but it is only 318 times as
massive. Jupiter's radius is about 1/10 the
radius of the Sun, and its mass is 0.001 times the
mass of the Sun, so the densities of the two bodies are similar. A "
Jupiter mass" (
MJ or
MJup) is often used as a unit to describe masses of other objects, particularly
extrasolar planets and
brown dwarfs. So, for example, the extrasolar planet
HD 209458 b has a mass of
0.69 MJ, while
Kappa Andromedae b has a mass of
12.8 MJ.
Theoretical models indicate that if Jupiter had much more mass than it does at present, it would shrink. For small changes in mass, the
radius would not change appreciably, and above about 500
M⊕ (1.6 Jupiter masses) the interior would become so much more compressed under the increased pressure that its volume would
decrease
despite the increasing amount of matter. As a result, Jupiter is
thought to have about as large a diameter as a planet of its composition
and evolutionary history can achieve. The process of further shrinkage with increasing mass would continue until appreciable
stellar ignition was achieved, as in high-mass
brown dwarfs having around 50 Jupiter masses.
Although Jupiter would need to be about 75 times as massive to
fuse hydrogen and become a
star, the smallest
red dwarf is only about 30 percent larger in radius than Jupiter.
Despite this, Jupiter still radiates more heat than it receives from
the Sun; the amount of heat produced inside it is similar to the total
solar radiation it receives. This additional heat is generated by the
Kelvin–Helmholtz mechanism through contraction. This process causes Jupiter to shrink by about 2 cm each year. When it was first formed, Jupiter was much hotter and was about twice its current diameter.
Internal structure
Jupiter is thought to consist of a dense
core with a mixture of elements, a surrounding layer of liquid
metallic hydrogen with some helium, and an outer layer predominantly of
molecular hydrogen. Beyond this basic outline, there is still considerable uncertainty. The core is often described as
rocky,
but its detailed composition is unknown, as are the properties of
materials at the temperatures and pressures of those depths (see below).
In 1997, the existence of the core was suggested by gravitational
measurements, indicating a mass of from 12 to 45 times that of Earth, or roughly 4%–14% of the total mass of Jupiter.
The presence of a core during at least part of Jupiter's history is
suggested by models of planetary formation that require the formation of
a rocky or icy core massive enough to collect its bulk of hydrogen and
helium from the
protosolar nebula.
Assuming it did exist, it may have shrunk as convection currents of hot
liquid metallic hydrogen mixed with the molten core and carried its
contents to higher levels in the planetary interior. A core may now be
entirely absent, as gravitational measurements are not yet precise
enough to rule that possibility out entirely.
The uncertainty of the models is tied to the error margin in hitherto measured parameters: one of the rotational coefficients (J
6) used to describe the planet's gravitational moment, Jupiter's equatorial radius, and its temperature at 1 bar pressure. The
Juno mission, which arrived in July 2016, is expected to further constrain the values of these parameters for better models of the core.
The core region may be surrounded by dense
metallic hydrogen, which extends outward to about 78% of the radius of the planet.
Rain-like droplets of helium and neon precipitate downward through this
layer, depleting the abundance of these elements in the upper
atmosphere.
Rainfalls of
diamonds have been suggested to occur on Jupiter, as well as on
Saturn and
ice giants Uranus and
Neptune.
Above the layer of metallic hydrogen lies a transparent interior
atmosphere of hydrogen. At this depth, the pressure and temperature are
above hydrogen's
critical pressure of 1.2858 MPa and
critical temperature of only 32.938
K.
In this state, there are no distinct liquid and gas phases—hydrogen is
said to be in a supercritical fluid state. It is convenient to treat
hydrogen as gas in the upper layer extending downward from the cloud
layer to a depth of about 1,000
km,
and as liquid in deeper layers. Physically, there is no clear
boundary—the gas smoothly becomes hotter and denser as one descends.
The temperature and pressure inside Jupiter increase steadily toward the core, due to the
Kelvin–Helmholtz mechanism. At the pressure level of 10
bars (1
MPa), the temperature is around 340 K (67 °C; 152 °F). At the
phase transition
region where hydrogen—heated beyond its critical point—becomes
metallic, it is calculated the temperature is 10,000 K (9,700 °C;
17,500 °F) and the pressure is
200 GPa. The temperature at the core boundary is estimated to be 36,000 K (35,700 °C; 64,300 °F) and the interior pressure is roughly
3,000–4,500 GPa.
This cut-away illustrates a model of the interior of Jupiter, with a rocky core overlaid by a deep layer of liquid metallic hydrogen.
Atmosphere
Jupiter has the largest planetary atmosphere in the
Solar System, spanning over 5,000 km (3,000 mi) in altitude.
Because Jupiter has no surface, the base of its atmosphere is usually
considered to be the point at which atmospheric pressure is equal to
100 kPa (1.0 bar).
Cloud layers
The movement of Jupiter's counter-rotating cloud bands. This looping animation maps the planet's exterior onto a cylindrical projection.
South polar view of Jupiter
Enhanced color view of Jupiter's southern storms
Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly
ammonium hydrosulfide. The clouds are located in the
tropopause and are arranged into bands of different latitudes, known as tropical regions. These are sub-divided into lighter-hued
zones and darker
belts. The interactions of these conflicting
circulation patterns cause storms and
turbulence.
Wind speeds of 100 m/s (360 km/h) are common in zonal jets.
The zones have been observed to vary in width, color and intensity from
year to year, but they have remained sufficiently stable for scientists
to give them identifying designations.
Jupiter clouds
(Juno; December 2017)
The cloud layer is only about 50 km (31 mi) deep, and consists of at
least two decks of clouds: a thick lower deck and a thin clearer region.
There may also be a thin layer of
water clouds underlying the ammonia layer. Supporting the idea of water clouds are the flashes of
lightning
detected in the atmosphere of Jupiter. These electrical discharges can
be up to a thousand times as powerful as lightning on Earth.
The water clouds are assumed to generate thunderstorms in the same way
as terrestrial thunderstorms, driven by the heat rising from the
interior.
The orange and brown coloration in the clouds of Jupiter are
caused by upwelling compounds that change color when they are exposed to
ultraviolet light from the Sun. The exact makeup remains uncertain, but the substances are thought to be phosphorus, sulfur or possibly
hydrocarbons. These colorful compounds, known as
chromophores, mix with the warmer, lower deck of clouds. The zones are formed when rising
convection cells form crystallizing ammonia that masks out these lower clouds from view.
Jupiter's low
axial tilt means that the poles constantly receive less
solar radiation than at the planet's equatorial region.
Convection within the interior of the planet transports more energy to the poles, balancing out the temperatures at the cloud layer.
Great Red Spot and other vortices
Time-lapse sequence from the approach of Voyager 1,
showing the motion of atmospheric bands and circulation of the Great
Red Spot. Recorded over 32 days with one photograph taken every 10 hours
(once per Jovian day).
The best known feature of Jupiter is the
Great Red Spot, a persistent
anticyclonic storm that is larger than Earth, located 22° south of the equator. It is known to have been in existence since at least 1831, and possibly since 1665. Images by the
Hubble Space Telescope have shown as many as two "red spots" adjacent to the Great Red Spot. The storm is large enough to be visible through Earth-based
telescopes with an
aperture of 12 cm or larger. The
oval object
rotates counterclockwise, with a
period of about six days. The maximum altitude of this storm is about 8 km (5 mi) above the surrounding cloudtops.
The Great Red Spot is large enough to accommodate Earth within its boundaries.
Mathematical models suggest that the storm is stable and may be a permanent feature of the planet.
However, it has significantly decreased in size since its discovery.
Initial observations in the late 1800s showed it to be approximately
41,000 km (25,500 mi) across. By the time of the
Voyager flybys in 1979, the storm had a length of 23,300 km (14,500 mi) and a width of approximately 13,000 km (8,000 mi).
Hubble
observations in 1995 showed it had decreased in size again to 20,950 km
(13,020 mi), and observations in 2009 showed the size to be 17,910 km
(11,130 mi). As of 2015, the storm was measured at approximately 16,500 by 10,940 km (10,250 by 6,800 mi), and is decreasing in length by about 930 km (580 mi) per year.
Storms such as this are common within the
turbulent atmospheres of
giant planets.
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 as little as a few hours or stretch
on for centuries.
Even before Voyager proved that the feature was a storm, there
was strong evidence that the spot could not be associated with any
deeper feature on the planet's surface, as the Spot rotates
differentially with respect to the rest of the atmosphere, sometimes
faster and sometimes more slowly.
In 2000, an atmospheric feature formed in the southern hemisphere
that is similar in appearance to the Great Red Spot, but smaller. This
was created when several smaller, white oval-shaped storms merged to
form a single feature—these three smaller white ovals were first
observed in 1938. The merged feature was named
Oval BA, and has been nicknamed Red Spot Junior. It has since increased in intensity and changed color from white to red.
In April 2017, scientists reported the discovery of a "Great Cold
Spot" in Jupiter's thermosphere at its north pole that is 24,000 km
(15,000 mi) across, 12,000 km (7,500 mi) wide, and 200 °C (360 °F)
cooler than surrounding material. The feature was discovered by
researchers at the
Very Large Telescope in Chile, who then searched archived data from the
NASA Infrared Telescope Facility
between 1995 and 2000. They found that, while the Spot changes size,
shape and intensity over the short term, it has maintained its general
position in the atmosphere across more than 15 years of available data.
Scientists believe the Spot is a giant vortex similar to the Great Red
Spot and also appears to be
quasi-stable like the
vortices
in Earth's thermosphere. Interactions between charged particles
generated from Io and the planet's strong magnetic field likely resulted
in redistribution of heat flow, forming the Spot.
Magnetosphere
Jupiter's
magnetic field is fourteen times as strong as that of Earth, ranging from 4.2
gauss (0.42
mT) at the equator to 10–14 gauss (1.0–1.4 mT) at the poles, making it the strongest in the Solar System (except for
sunspots). This field is thought to be generated by
eddy currents—swirling movements of conducting materials—within the liquid metallic hydrogen core. The volcanoes on the moon
Io emit large amounts of
sulfur dioxide forming a gas torus along the moon's orbit. The gas is ionized in the magnetosphere producing
sulfur and
oxygen ions. They, together with hydrogen ions originating from the atmosphere of Jupiter, form a
plasma sheet
in Jupiter's equatorial plane. The plasma in the sheet co-rotates with
the planet causing deformation of the dipole magnetic field into that of
magnetodisk. Electrons within the plasma sheet generate a strong radio
signature that produces bursts in the range of 0.6–30
MHz.
At about 75 Jupiter radii from the planet, the interaction of the magnetosphere with the
solar wind generates a
bow shock. Surrounding Jupiter's magnetosphere is a
magnetopause, located at the inner edge of a
magnetosheath—a region between it and the bow shock. The solar wind interacts with these regions, elongating the magnetosphere on Jupiter's
lee side
and extending it outward until it nearly reaches the orbit of Saturn.
The four largest moons of Jupiter all orbit within the magnetosphere,
which protects them from the solar wind.
The magnetosphere of Jupiter is responsible for intense episodes of
radio emission
from the planet's polar regions. Volcanic activity on Jupiter's moon Io injects gas into Jupiter's magnetosphere, producing a torus
of particles about the planet. As Io moves through this torus, the
interaction generates
Alfvén waves that carry ionized matter into the polar regions of Jupiter. As a result, radio waves are generated through a
cyclotron maser mechanism,
and the energy is transmitted out along a cone-shaped surface. When
Earth intersects this cone, the radio emissions from Jupiter can exceed
the solar radio output.
Orbit and rotation
Jupiter (red) completes one orbit of the Sun (center) for every 11.86 orbits of Earth (blue)
Jupiter is the only planet whose
barycenter with the Sun lies outside the volume of the Sun, though by only 7% of the Sun's radius.
The average distance between Jupiter and the Sun is 778 million km
(about 5.2 times the average distance between Earth and the Sun, or 5.2
AU) and it completes an orbit every 11.86 years. This is approximately two-fifths the orbital period of Saturn, forming a near
orbital resonance between the two largest planets in the Solar System. The elliptical orbit of Jupiter is inclined 1.31° compared to Earth. Because the
eccentricity of its orbit is 0.048, Jupiter's distance from the Sun varies by 75 million km between its nearest approach (
perihelion) and furthest distance (
aphelion).
The
axial tilt
of Jupiter is relatively small: only 3.13°. As a result, it does not
experience significant seasonal changes, in contrast to, for example,
Earth and Mars.
Jupiter's
rotation is the fastest of all the Solar System's planets, completing a rotation on its
axis in slightly less than ten hours; this creates an
equatorial bulge easily seen through an Earth-based amateur
telescope. The planet is shaped as an
oblate spheroid, meaning that the diameter across its
equator is longer than the diameter measured between its
poles. On Jupiter, the equatorial diameter is 9,275 km (5,763 mi) longer than the diameter measured through the poles.
Because Jupiter is not a solid body, its upper atmosphere undergoes
differential rotation.
The rotation of Jupiter's polar atmosphere is about 5 minutes longer
than that of the equatorial atmosphere; three systems are used as frames
of reference, particularly when graphing the motion of atmospheric
features. System I applies from the latitudes 10° N to 10° S; its period
is the planet's shortest, at 9h 50m 30.0s. System II applies at all
latitudes north and south of these; its period is 9h 55m 40.6s. System
III was first defined by
radio astronomers, and corresponds to the rotation of the planet's magnetosphere; its period is Jupiter's official rotation.
Observation
Conjunction of Jupiter and the Moon
The retrograde motion of an outer planet is caused by its relative location with respect to Earth
Jupiter is usually the fourth brightest object in the sky (after the Sun, the
Moon and
Venus); at times
Mars appears brighter than Jupiter. Depending on Jupiter's position with respect to the
Earth, it can vary in visual magnitude from as bright as −2.94 at
opposition down to −1.66 during
conjunction with the Sun. The mean apparent magnitude is -2.20 with a standard deviation of 0.33. The
angular diameter of Jupiter likewise varies from 50.1 to 29.8
arc seconds. Favorable oppositions occur when Jupiter is passing through
perihelion, an event that occurs once per orbit.
Earth overtakes Jupiter every 398.9 days as it orbits the Sun, a duration called the
synodic period. As it does so, Jupiter appears to undergo
retrograde motion
with respect to the background stars. That is, for a period Jupiter
seems to move backward in the night sky, performing a looping motion.
Because the orbit of Jupiter is outside that of Earth, the
phase angle
of Jupiter as viewed from Earth never exceeds 11.5°. That is, the
planet always appears nearly fully illuminated when viewed through
Earth-based telescopes. It was only during spacecraft missions to
Jupiter that crescent views of the planet were obtained. A small telescope will usually show Jupiter's four
Galilean moons and the prominent cloud belts across
Jupiter's atmosphere. A large telescope will show Jupiter's
Great Red Spot when it faces Earth.
Mythology
Jupiter, woodcut from a 1550 edition of Guido Bonatti's Liber Astronomiae
The planet Jupiter has been known since ancient times. It is visible
to the naked eye in the night sky and can occasionally be seen in the
daytime when the Sun is low. To the
Babylonians, this object represented their god
Marduk. They used Jupiter's roughly 12-year orbit along the
ecliptic to define the
constellations of their
zodiac.
The Romans called it "the star of
Jupiter" (
Iuppiter Stella), as they believed it to be sacred to the principal
god of
Roman mythology, whose name comes from the
Proto-Indo-European vocative compound *
Dyēu-pəter (nominative: *
Dyēus-pətēr, meaning "Father Sky-God", or "Father Day-God"). In turn, Jupiter was the counterpart to the
mythical Greek Zeus (Ζεύς), also referred to as
Dias (Δίας), the planetary name of which is retained in modern
Greek. The ancient Greeks knew the planet as
Phaethon, meaning "shining one".
The
astronomical symbol for the planet,
, is a stylized representation of the god's lightning bolt. The original Greek deity
Zeus supplies the root
zeno-, used to form some Jupiter-related words, such as
zenographic.
The Chinese, Vietnamese, Koreans and Japanese called it the "wood star" (
Chinese:
木星;
pinyin:
mùxīng), based on the Chinese
Five Elements. Chinese Taoism personified it as the
Fu star. The Greeks called it
Φαέθων (
Phaethon, meaning "blazing").
In
Vedic astrology, Hindu astrologers named the planet after
Brihaspati, the religious teacher of the gods, and often called it "
Guru", which literally means the "Heavy One".
In the
Central Asian-Turkic myths, Jupiter is called
Erendiz or
Erentüz, from
eren (of uncertain meaning) and
yultuz ("star"). There are many theories about the meaning of
eren.
These peoples calculated the period of the orbit of Jupiter as 11 years
and 300 days. They believed that some social and natural events
connected to Erentüz's movements on the sky.
History of research and exploration
Pre-telescopic research
Model in the Almagest of the longitudinal motion of Jupiter (☉) relative to Earth (⊕)
The observation of Jupiter dates back to at least the
Babylonian astronomers of the 7th or 8th century BC. The ancient Chinese also observed the orbit of
Suìxīng (
歲星) and established their cycle of 12
earthly branches based on its approximate number of years; the
Chinese language still uses its name (
simplified as
岁) when referring to years of age. By the 4th century BC, these observations had developed into the
Chinese zodiac, with each year associated with a
Tai Sui star and
god controlling the region of the heavens opposite Jupiter's position in the night sky; these beliefs survive in some
Taoist religious practices and in the East Asian zodiac's twelve animals, now often
popularly assumed to be related to the arrival of the animals before
Buddha. The Chinese historian
Xi Zezong has claimed that
Gan De, an ancient
Chinese astronomer, discovered one of
Jupiter's moons in 362 BC with the unaided eye. If accurate, this would predate Galileo's discovery by nearly two millennia. In his 2nd century work the
Almagest, the Hellenistic astronomer
Claudius Ptolemaeus constructed a
geocentric planetary model based on
deferents and
epicycles to explain Jupiter's motion relative to Earth, giving its orbital period around Earth as 4332.38 days, or 11.86 years.
Ground-based telescope research
In 1610, Italian polymath
Galileo Galilei discovered the four largest
moons of Jupiter (now known as the
Galilean moons) using a telescope; thought to be the first telescopic observation of moons other than Earth's. One day after Galileo,
Simon Marius independently discovered moons around Jupiter, though he did not publish his discovery in a book until 1614. It was Marius's names for the four major moons, however, that stuck—Io, Europa, Ganymede and
Callisto. These findings were also the first discovery of
celestial motion not apparently centered on Earth. The discovery was a major point in favor 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.
During the 1660s,
Giovanni Cassini
used a new telescope to discover spots and colorful bands on Jupiter
and observed that the planet appeared oblate; that is, flattened at the
poles. He was also able to estimate the rotation period of the planet. In 1690 Cassini noticed that the atmosphere undergoes
differential rotation.
The Great Red Spot, a prominent oval-shaped feature in the
southern hemisphere of Jupiter, may have been observed as early as 1664
by
Robert Hooke and in 1665 by Cassini, although this is disputed. The pharmacist
Heinrich Schwabe produced the earliest known drawing to show details of the Great Red Spot in 1831.
The Red Spot was reportedly lost from sight on several occasions
between 1665 and 1708 before becoming quite conspicuous in 1878. It was
recorded as fading again in 1883 and at the start of the 20th century.
Both
Giovanni Borelli
and Cassini made careful tables of the motions of Jupiter's moons,
allowing predictions of the times when the moons would pass before or
behind the planet. By the 1670s, it was observed that when Jupiter was
on the opposite side of the Sun from Earth, these events would occur
about 17 minutes later than expected.
Ole Rømer deduced that light does not travel instantaneously (a conclusion that Cassini had earlier rejected), and this timing discrepancy was used to estimate the
speed of light.
In 1892,
E. E. Barnard observed a fifth satellite of Jupiter with the 36-inch (910 mm) refractor at
Lick Observatory
in California. The discovery of this relatively small object, a
testament to his keen eyesight, quickly made him famous. This moon was
later named
Amalthea. It was the last planetary moon to be discovered directly by visual observation.
In 1932,
Rupert Wildt identified absorption bands of ammonia and methane in the spectra of Jupiter.
Three long-lived anticyclonic features termed white ovals were
observed in 1938. For several decades they remained as separate features
in the atmosphere, sometimes approaching each other but never merging.
Finally, two of the ovals merged in 1998, then absorbed the third in
2000, becoming
Oval BA.
Radiotelescope research
In 1955, Bernard Burke and
Kenneth Franklin detected bursts of radio signals coming from Jupiter at 22.2 MHz.
The period of these bursts matched the rotation of the planet, and they
were also able to use this information to refine the rotation rate.
Radio bursts from Jupiter were found to come in two forms: long bursts
(or L-bursts) lasting up to several seconds, and short bursts (or
S-bursts) that had a duration of less than a hundredth of a second.
Scientists discovered that there were three forms of radio signals transmitted from Jupiter.
- Decametric radio bursts (with a wavelength of tens of meters)
vary with the rotation of Jupiter, and are influenced by interaction of
Io with Jupiter's magnetic field.
- Decimetric radio emission (with wavelengths measured in centimeters) was first observed by Frank Drake and Hein Hvatum in 1959. The origin of this signal was from a torus-shaped belt around Jupiter's equator. This signal is caused by cyclotron radiation from electrons that are accelerated in Jupiter's magnetic field.
- Thermal radiation is produced by heat in the atmosphere of Jupiter.
Exploration
Since 1973 a number of automated spacecraft have visited Jupiter, most notably the
Pioneer 10
space probe, the first spacecraft to get close enough to Jupiter to
send back revelations about the properties and phenomena of the Solar
System's largest planet.
Flights to other planets within the Solar System are accomplished at a
cost in energy, which is described by the net change in velocity of the
spacecraft, or
delta-v. Entering a
Hohmann transfer orbit from Earth to Jupiter from
low Earth orbit requires a delta-v of 6.3 km/s which is comparable to the 9.7 km/s delta-v needed to reach low Earth orbit.
Gravity assists through planetary
flybys can be used to reduce the energy required to reach Jupiter, albeit at the cost of a significantly longer flight duration.
Flyby missions
Perijove 6 pass of Jupiter as viewed by JunoCam
Flyby missions
| Spacecraft
|
Closest
approach
|
Distance
|
| Pioneer 10
|
December 3, 1973
|
130,000 km
|
| Pioneer 11
|
December 4, 1974
|
34,000 km
|
| Voyager 1
|
March 5, 1979
|
349,000 km
|
| Voyager 2
|
July 9, 1979
|
570,000 km
|
| Ulysses
|
February 8, 1992
|
408,894 km
|
| February 4, 2004
|
120,000,000 km
|
| Cassini
|
December 30, 2000
|
10,000,000 km
|
| New Horizons
|
February 28, 2007
|
2,304,535 km
|
Beginning in 1973, several spacecraft have performed planetary flyby
maneuvers that brought them within observation range of Jupiter. The
Pioneer
missions obtained the first close-up images of Jupiter's atmosphere and
several of its moons. They discovered that the radiation fields near
the planet were much stronger than expected, but both spacecraft managed
to survive in that environment. The trajectories of these spacecraft
were used to refine the mass estimates of the Jovian system.
Radio occultations by the planet resulted in better measurements of Jupiter's diameter and the amount of polar flattening.
Six years later, the
Voyager missions vastly improved the understanding of the
Galilean moons
and discovered Jupiter's rings. They also confirmed that the Great Red
Spot was anticyclonic. Comparison of images showed that the Red Spot had
changed hue since the Pioneer missions, turning from orange to dark
brown. A torus of ionized atoms was discovered along Io's orbital path,
and volcanoes were found on the moon's surface, some in the process of
erupting. As the spacecraft passed behind the planet, it observed
flashes of lightning in the night side atmosphere.
The next mission to encounter Jupiter was the
Ulysses solar probe. It performed a flyby maneuver to attain a
polar orbit around the Sun. During this pass, the spacecraft conducted studies on Jupiter's magnetosphere.
Ulysses has no cameras so no images were taken. A second flyby six years later was at a much greater distance.
Cassini views Jupiter and Io on January 1, 2001
In 2000, the
Cassini probe flew by Jupiter on its way to
Saturn, and provided some of the highest-resolution images ever made of the planet.
The
New Horizons probe flew by Jupiter for a gravity assist en route to
Pluto. Its closest approach was on February 28, 2007.
The probe's cameras measured plasma output from volcanoes on Io and
studied all four Galilean moons in detail, as well as making
long-distance observations of the outer moons
Himalia and
Elara. Imaging of the Jovian system began September 4, 2006.
Galileo mission
Jupiter as seen by the space probe Cassini
The first spacecraft to orbit Jupiter was the
Galileo probe, which entered orbit on December 7, 1995. It orbited the planet for over seven years, conducting multiple flybys of all the Galilean moons and
Amalthea. The spacecraft also witnessed the impact of
Comet Shoemaker–Levy 9
as it approached Jupiter in 1994, giving a unique vantage point for the
event. Its originally designed capacity was limited by the failed
deployment of its high-gain radio antenna, although extensive
information was still gained about the Jovian system from
Galileo.
A 340-kilogram titanium
atmospheric probe was released from the spacecraft in July 1995, entering Jupiter's atmosphere on December 7. It parachuted through 150 km (93 mi) of the atmosphere at a speed of about 2,575 km/h (1600 mph) and collected data for 57.6 minutes before the signal was lost at a pressure of about 23
atmospheres at a temperature of 153 °C. It melted thereafter, and possibly vaporized. 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 to avoid any possibility of it crashing into and
possibly contaminating Europa, a moon which has been hypothesized to
have the possibility of
harboring life.
Data from this mission revealed that hydrogen composes up to 90% of Jupiter's atmosphere.
The recorded temperature was more than 300 °C (>570 °F) and the
windspeed measured more than 644 km/h (>400 mph) before the probes
vaporised.
Juno mission
NASA's
Juno mission arrived at Jupiter on July 4, 2016, and is expected to complete 37 orbits over the next 20 months. The mission plan called for
Juno to study the planet in detail from a
polar orbit.
On August 27, 2016, the spacecraft completed its first fly-by of
Jupiter and sent back the first-ever images of Jupiter’s north pole.
Future probes
Canceled missions
There has been great interest in studying the icy moons in detail
because of the possibility of subsurface liquid oceans on Jupiter's
moons Europa, Ganymede, and Callisto. Funding difficulties have delayed
progress. NASA's
JIMO (
Jupiter Icy Moons Orbiter) was cancelled in 2005. A subsequent proposal was developed for a joint
NASA/
ESA mission called
EJSM/Laplace, with a provisional launch date around 2020. EJSM/Laplace would have consisted of the NASA-led
Jupiter Europa Orbiter and the ESA-led
Jupiter Ganymede Orbiter.
However, ESA had formally ended the partnership by April 2011, citing
budget issues at NASA and the consequences on the mission timetable.
Instead, ESA planned to go ahead with a European-only mission to compete
in its L1
Cosmic Vision selection.
Moons
Jupiter has 79 known
natural satellites.
Of these, 63 are less than 10 kilometres in diameter and have only been
discovered since 1975. The four largest moons, visible from Earth with
binoculars on a clear night, known as the "
Galilean moons", are Io, Europa, Ganymede, and Callisto.
Galilean moons
The moons discovered by Galileo—Io, Europa, Ganymede, and
Callisto—are among the largest satellites in the Solar System. The
orbits of three of them (Io, Europa, and Ganymede) 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 large moons to distort their orbits into
elliptical shapes, because each moon receives an extra tug from its
neighbors at the same point in every orbit it makes. The
tidal force from Jupiter, on the other hand, works to
circularize their orbits.
The
eccentricity
of their orbits causes regular flexing of the three moons' shapes, with
Jupiter's gravity stretching them out as they approach it and allowing
them to spring back to more spherical shapes as they swing away. This
tidal flexing
heats the moons' interiors by
friction. This is seen most dramatically in the extraordinary
volcanic activity of innermost Io (which is subject to the strongest tidal forces), and to a lesser degree in the geological youth of
Europa's surface (indicating recent resurfacing of the moon's exterior).
The Galilean moons, compared to Earth's Moon
| Name
|
IPA
|
Diameter
|
Mass
|
Orbital radius
|
Orbital period
|
| km
|
%
|
kg
|
%
|
km
|
%
|
days
|
%
|
| Io
|
/ˈaɪ.oʊ/
|
3,643
|
105
|
8.9×1022
|
120
|
421,700
|
110
|
1.77
|
7
|
| Europa
|
/jʊˈroʊpə/
|
3,122
|
90
|
4.8×1022
|
65
|
671,034
|
175
|
3.55
|
13
|
| Ganymede
|
/ˈɡænimiːd/
|
5,262
|
150
|
14.8×1022
|
200
|
1,070,412
|
280
|
7.15
|
26
|
| Callisto
|
/kəˈlɪstoʊ/
|
4,821
|
140
|
10.8×1022
|
150
|
1,882,709
|
490
|
16.69
|
61
|
|
|
|
| The Galilean moons Io, Europa, Ganymede, Callisto (in order of increasing distance from Jupiter)
|
Classification
Before the discoveries of the Voyager missions, Jupiter's moons were
arranged neatly into four groups of four, based on commonality of their
orbital elements.
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 sub-division is a grouping of the eight inner regular
moons, which have nearly circular orbits near the plane of Jupiter's
equator and are thought to have formed with Jupiter. The remainder of
the moons consist of an unknown number of small irregular moons with
elliptical and inclined orbits, which are thought to be captured
asteroids or fragments of captured asteroids. Irregular moons that
belong to a group share similar orbital elements and thus may have a
common origin, perhaps as a larger moon or captured body that broke up.
| Regular moons
|
| Inner group
|
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.
|
| Galilean moons
|
These four moons, discovered by Galileo Galilei and by Simon Marius in parallel, orbit between 400,000 and 2,000,000 km, and are some of the largest moons in the Solar System.
|
| Irregular moons
|
| Themisto
|
This is a single moon belonging to a group of its own, orbiting halfway between the Galilean moons and the Himalia group.
|
| Himalia group
|
A tightly clustered group of moons with orbits around 11,000,000–12,000,000 km from Jupiter.
|
| Carpo
|
Another isolated case; at the inner edge of the Ananke group, it orbits Jupiter in prograde direction.
|
| Valetudo
|
A third isolated case, which has a prograde orbit but overlaps the
retrograde groups listed below; this may result in a future collision.
|
| Ananke group
|
This retrograde orbit group has rather indistinct borders, averaging 21,276,000 km from Jupiter with an average inclination of 149 degrees.
|
| Carme group
|
A fairly distinct retrograde group that averages 23,404,000 km from Jupiter with an average inclination of 165 degrees.
|
| Pasiphae group
|
A dispersed and only vaguely distinct retrograde group that covers all the outermost moons.
|
Planetary rings
Jupiter has a faint
planetary ring system composed of three main segments: an inner
torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring. These rings appear to be made of dust, rather than ice as with Saturn's rings. The main ring is probably made of material ejected from the satellites
Adrastea and
Metis.
Material that would normally fall back to the moon is pulled into
Jupiter because of its strong gravitational influence. The orbit of the
material veers towards Jupiter and new material is added by additional
impacts. In a similar way, the moons
Thebe and
Amalthea probably produce the two distinct components of the dusty gossamer ring. There is also evidence of a rocky ring strung along Amalthea's orbit which may consist of collisional debris from that moon.
Interaction with the Solar System
Along with its moons, Jupiter's gravitational field controls numerous
asteroids that 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 more than two thousand have been discovered. The largest is
624 Hektor.
Most
short-period comets belong to the Jupiter family—defined as comets with
semi-major axes smaller than Jupiter's. Jupiter family comets are thought to form in the
Kuiper belt outside the orbit of Neptune. During close encounters with Jupiter their orbits are
perturbed into a smaller period and then circularized by regular gravitational interaction with the Sun and Jupiter.
Due to the magnitude of Jupiter's mass, the center of gravity between it and the Sun lies just above the Sun's surface. Jupiter is the only body in the Solar System for which this is true.
Impacts
Jupiter has been called the Solar System's vacuum cleaner, because of its immense
gravity well and location near the inner Solar System. It receives the most frequent comet impacts of the Solar System's planets. It was thought that the planet served to partially shield the inner system from cometary bombardment.
However, recent computer simulations suggest that Jupiter does not
cause a net decrease in the number of comets that pass through the inner
Solar System, as its gravity perturbs their orbits inward roughly as
often as it accretes or ejects them. This topic remains controversial among scientists, as some think it draws comets towards Earth from the
Kuiper belt while others think that Jupiter protects Earth from the alleged
Oort cloud. Jupiter experiences about 200 times more
asteroid and
comet impacts than Earth.
A 1997 survey of early astronomical records and drawings suggested that a certain dark surface feature discovered by astronomer
Giovanni Cassini
in 1690 may have been an impact scar. The survey initially produced
eight more candidate sites as potential impact observations that he and
others had recorded between 1664 and 1839. It was later determined,
however, that these candidate sites had little or no possibility of
being the results of the proposed impacts.
More recent discoveries include the following:
- A fireball was photographed by Voyager 1 during its Jupiter encounter in March 1979.
- During the period July 16, 1994, to July 22, 1994, over 20 fragments from the comet Shoemaker–Levy 9 (SL9, formally designated D/1993 F2) collided with Jupiter's southern hemisphere,
providing the first direct observation of a collision between two Solar
System objects. This impact provided useful data on the composition of
Jupiter's atmosphere.
- On July 19, 2009, an impact site was discovered at approximately 216 degrees longitude in System 2. This impact left behind a black spot in Jupiter's atmosphere, similar in size to Oval BA.
Infrared observation showed a bright spot where the impact took place,
meaning the impact warmed up the lower atmosphere in the area near
Jupiter's south pole.
- A fireball, smaller than the previous observed impacts, was detected on June 3, 2010, by Anthony Wesley, an amateur astronomer in Australia, and was later discovered to have been captured on video by another amateur astronomer in the Philippines.
- Yet another fireball was seen on August 20, 2010.
- On September 10, 2012, another fireball was detected.
- On March 17, 2016 an asteroid or comet struck and was filmed on video.
