Jupiter
From Wikipedia, the free encyclopedia
Jupiter is the fifth
planet from the
Sun and the
largest planet in the
Solar System. It is a
gas giant with
mass
one-thousandth of that of the Sun but is two and a half times the mass
of all the other planets in the Solar System combined. Jupiter is
classified as a gas giant along with
Saturn,
Uranus and
Neptune. Together, these four planets are sometimes referred to as the
Jovian or outer planets.
The planet was known by
astronomers of ancient times.
[11] The
Romans named the planet after the
Roman god Jupiter.
[12] When viewed from
Earth, Jupiter can reach an
apparent magnitude of −2.94, bright enough to cast shadows,
[13] and making it on average the third-brightest object in the
night sky after the
Moon and
Venus. (
Mars can briefly match Jupiter's brightness at
certain points in its orbit.)
Jupiter is primarily composed of
hydrogen with a quarter of its mass being
helium, although helium only comprises about a tenth of the number of molecules. It may also have a rocky core of heavier elements,
[14]
but like the other gas giants, Jupiter lacks a well-defined solid
surface. Because of its rapid rotation, the planet's shape is that of an
oblate spheroid
(it possesses 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. There are also at least 67 moons, including the four large moons called the
Galilean moons that were first discovered by
Galileo Galilei in 1610.
Ganymede, the largest of these moons, 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. The most recent probe to visit Jupiter was the
Pluto-bound
New Horizons spacecraft in late February 2007. The probe
used the gravity
from Jupiter to increase its speed. Future targets for exploration in
the Jovian system include the possible ice-covered liquid ocean on the
moon
Europa.
Structure
Jupiter is composed primarily of
gaseous and
liquid matter. It is the largest of four
gas giants as well as the largest
planet in the
Solar System with a diameter of 142,984 km (88,846 mi) at its
equator.
The density of Jupiter, 1.326 g/cm
3, is the second highest of the gas giants, but lower than for any of the four
terrestrial planets.
Composition
Jupiter's upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume or fraction of gas
molecules. Since a helium
atom has about four times as much
mass as a
hydrogen atom, the composition changes when described as the proportion of mass contributed by different atoms. Thus, the
atmosphere
is approximately 75% hydrogen and 24% helium by mass, with the
remaining one percent of the mass consisting of other elements. The
interior contains denser materials such that the distribution is roughly
71% hydrogen, 24% helium and 5% other elements by mass. 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.
[15][16] Through
infrared and
ultraviolet measurements, trace amounts of
benzene and other
hydrocarbons have also been found.
[17]
The atmospheric proportions of hydrogen and helium are very 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.
[18] 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.
[19] Abundances of heavier inert gases in Jupiter's atmosphere are about two to three times that of the Sun.
Based on
spectroscopy,
Saturn is thought to be similar in composition to Jupiter, but the other gas giants
Uranus and
Neptune have relatively much less hydrogen and helium.
[20]
Because of the lack of atmospheric entry probes, high-quality abundance
numbers of the heavier elements are lacking for the outer planets
beyond Jupiter.
Mass
Jupiter's diameter is one
order of magnitude
smaller (×0.10045) than the Sun, and one order of magnitude larger
(×10.9733) than the Earth. The Great Red Spot has roughly the same size
as the circumference of the 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. Although this planet dwarfs the Earth with a
diameter 11 times as great, it is considerably less dense. Jupiter's
volume is that of about 1,321 Earths, yet the planet is only 318 times
as massive.
[3][21] Jupiter's radius is about 1/10 the
radius of the Sun,
[22] and its mass is 0.001 times the
mass of the Sun, so the density of the two bodies is similar.
[23] A "
Jupiter mass" (M
J or M
Jup) 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 M
J, while
Kappa Andromedae b has a mass of 12.8 M
J.
[24]
Theoretical models indicate that if Jupiter had much more mass than it does at present, the planet would shrink.
[25] For small changes in mass, the
radius would not change appreciably, and above about 500
M⊕ (1.6 Jupiter masses)
[25] the interior would become so much more compressed under the increased gravitation force that the planet's 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 is achieved as in high-mass
brown dwarfs around 50 Jupiter masses.
[26]
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.
[27][28]
Despite this, Jupiter still radiates more heat than it receives from
the Sun; the amount of heat produced inside the planet is similar to the
total
solar radiation it receives.
[29] This additional heat radiation is generated by the
Kelvin–Helmholtz mechanism through contraction. This process results in the planet shrinking by about 2 cm each year.
[30] When it was first formed, Jupiter was much hotter and was about twice its current diameter.
[31]
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.
[30]
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,
[30] indicating a mass of from 12 to 45 times the Earth's mass or roughly 4%–14% of the total mass of Jupiter.
[29][32]
The presence of a core during at least part of Jupiter's history is
suggested by models of planetary formation involving initial formation
of a rocky or icy core that is 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, because gravitational measurements are not yet precise
enough to rule that possibility out entirely.
[30][33]
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 launched in August 2011, is expected to better constrain the
values of these parameters, and thereby make progress on the problem of
the core.
[34]
The core region is surrounded by dense
metallic hydrogen, which extends outward to about 78 percent of the radius of the planet.
[29]
Rain-like droplets of helium and neon precipitate downward through this
layer, depleting the abundance of these elements in the upper
atmosphere.
[19][35]
Above the layer of metallic hydrogen lies a transparent interior
atmosphere of hydrogen. At this depth, the temperature is above the
critical temperature, which for hydrogen is only 33
K[36] (see
hydrogen).
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,
[29]
and as liquid in deeper layers. Physically, there is no clear
boundary—the gas smoothly becomes hotter and denser as one descends.
[37][38]
The temperature and pressure inside Jupiter increase steadily toward the core. At the "surface" pressure level of 10
bars, the temperature is around 340
K. At the
phase transition region where hydrogen—heated beyond its critical point—becomes metallic, it is believed the temperature is
10,000 K and the pressure is
200 GPa. The temperature at the core boundary is estimated to be 36,000 K and the interior pressure is roughly
3,000–4,500 GPa.
[29]
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 (3,107 mi) in altitude.
[39][40]
As Jupiter has no surface, the base of its atmosphere is usually
considered to be the point at which atmospheric pressure is equal to
1 MPa (10 bar), or ten times surface pressure on Earth.
[39]
Cloud layers
This 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 mi) from Jupiter. The white oval storm directly below the
Great Red Spot is approximately the same diameter as Earth.
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.
[41]
The zones have been observed to vary in width, color and intensity from
year to year, but they have remained sufficiently stable for
astronomers to give them identifying designations.
[21]
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, as evidenced by flashes of
lightning detected in the atmosphere of Jupiter. This is caused by water's
polarity, which makes it capable of creating the charge separation needed to produce lightning.
[29] These electrical discharges can be up to a thousand times as powerful as lightning on the Earth.
[42] The water clouds can form thunderstorms driven by the heat rising from the interior.
[43]
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 believed to be phosphorus, sulfur or possibly
hydrocarbons.
[29][44] 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.
[45]
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.
[21]
Great Red Spot and other vortices
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. Latest evidence by the
Hubble Space Telescope shows there are three "red spots" adjacent to the Great Red Spot
[47] It is known to have been in existence since at least 1831,
[48] and possibly since 1665.
[49][50] Mathematical models suggest that the storm is stable and may be a permanent feature of the planet.
[51] The storm is large enough to be visible through Earth-based
telescopes with an
aperture of
12 cm or larger.
[52]
Time-lapse sequence (over 1 month) from the approach of
Voyager 1 to Jupiter, showing the motion of atmospheric bands, and circulation of the Great Red Spot.
The
oval object
rotates counterclockwise, with a
period of about six days.
[53] 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's diameter.
[54] The maximum altitude of this storm is about 8 km (5 mi) above the surrounding cloudtops.
[55]
Storms such as this are common 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 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. During its recorded history it has traveled several times
around the planet relative to any possible fixed rotational marker below
it.
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.
[56][57][58]
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.
[59] These rings appear to be made of dust, rather than ice as with Saturn's rings.
[29] 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.
[60] In a similar way, the moons
Thebe and
Amalthea probably produce the two distinct components of the dusty gossamer ring.
[60] There is also evidence of a rocky ring strung along Amalthea's orbit which may consist of collisional debris from that moon.
[61]
Magnetosphere
Aurora on Jupiter. Three bright dots are created by magnetic
flux tubes
that connect to the Jovian moons Io (on the left), Ganymede (on the
bottom) and Europa (also on the bottom). In addition, the very bright
almost circular region, called the main oval, and the fainter polar
aurora can be seen.
Jupiter's broad
magnetic field is 14 times as strong as the Earth's, 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).
[45] This field is believed 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.
[62]
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.
[29]
The magnetosphere of Jupiter is responsible for intense episodes of
radio
emission from the planet's polar regions. Volcanic activity on the
Jovian moon Io (see below) 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 the
Earth intersects this cone, the radio emissions from Jupiter can exceed
the solar radio output.
[63]
Orbit and rotation
Jupiter (red) completes one orbit of the Sun (center) for every 11.86 orbits of the Earth (blue)
Jupiter is the only planet that has a
center of mass with the Sun that lies outside the volume of the Sun, though by only 7% of the Sun's radius.
[64]
The average distance between Jupiter and the Sun is 778 million km
(about 5.2 times the average distance from the Earth to the Sun, or 5.2
AU) and it completes an orbit every 11.86 years. This is two-fifths the orbital period of
Saturn, forming a 5:2
orbital resonance between the two largest planets in the Solar System.
[65] The elliptical orbit of Jupiter is inclined 1.31° compared to the Earth. Because of an
eccentricity of 0.048, the distance from Jupiter and the Sun varies by 75 million km between
perihelion and
aphelion, or the nearest and most distant points of the planet along the orbital path respectively.
The
axial tilt of Jupiter is relatively small: only 3.13°. As a result this planet does not experience significant
seasonal changes, in contrast to Earth and Mars for example.
[66]
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.
[38]
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.
[67]
Observation
Conjunction of Jupiter and the Moon
The retrograde motion of an outer planet is caused by its relative location with respect to the Earth.
Jupiter is usually the fourth brightest object in the sky (after the Sun, the
Moon and
Venus);
[45] 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 −2.9 at
opposition down to −1.6 during
conjunction with the Sun. The
angular diameter of Jupiter likewise varies from 50.1 to 29.8
arc seconds.
[3]
Favorable oppositions occur when Jupiter is passing through
perihelion,
an event that occurs once per orbit. As Jupiter approached perihelion
in March 2011, there was a favorable opposition in September 2010.
[68]
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.
Jupiter's 12-year orbital period corresponds to the dozen
astrological signs of the
zodiac, and may have been the historical origin of the signs.
[21] That is, each time Jupiter reaches opposition it has advanced eastward by about 30°, the width of a zodiac sign.
Because the orbit of Jupiter is outside the Earth's, the
phase angle
of Jupiter as viewed from the 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.
[69] A small telescope will usually show Jupiter's four
Galilean Moons and the prominent cloud belts across
Jupiter's atmosphere.
[70] A large telescope will show Jupiter's
Great Red Spot when it faces the Earth.
Research and exploration
Pre-telescopic research
Model in the
Almagest of the longitudinal motion of Jupiter (☉) relative to the Earth (⊕).
The observation of Jupiter dates back to the
Babylonian astronomers of the 7th or 8th century BC.
[71] The Chinese historian of astronomy,
Xi Zezong, has claimed that
Gan De, a
Chinese astronomer, made the discovery of one of
Jupiter's moons in 362 BC with the unaided eye. If accurate, this would predate Galileo's discovery by nearly two millennia.
[72][73] 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 the Earth, giving its orbital period around the Earth as 4332.38 days, or 11.86 years.
[74] In 499,
Aryabhata, a
mathematician-
astronomer from the classical age of
Indian mathematics and
astronomy, also used a geocentric model to estimate Jupiter's period as 4332.2722 days, or 11.86 years.
[75]
Ground-based telescope research
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; thought to be the first telescopic observation of moons
other than Earth's. Galileo's was also the first discovery of a
celestial motion not apparently centered on the Earth. It 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.
[76]
During the 1660s, 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.
[16] In 1690 Cassini noticed that the atmosphere undergoes
differential rotation.
[29]
False-color detail of Jupiter's atmosphere, imaged by
Voyager 1, showing the Great Red Spot and a passing white oval.
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
Giovanni Cassini, although this is disputed. The pharmacist
Heinrich Schwabe produced the earliest known drawing to show details of the Great Red Spot in 1831.
[77]
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.
[78]
Both
Giovanni Borelli
and Cassini made careful tables of the motions of the Jovian 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 the Earth, these events would occur
about 17 minutes later than expected.
Ole Rømer deduced that sight is not instantaneous (a conclusion that Cassini had earlier rejected),
[16] and this timing discrepancy was used to estimate the
speed of light.
[79]
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. The moon was later named
Amalthea.
[80] It was the last planetary moon to be discovered directly by visual observation.
[81] An additional eight satellites were subsequently discovered before the flyby of the
Voyager 1 probe in 1979.
In 1932,
Rupert Wildt identified absorption bands of ammonia and methane in the spectra of Jupiter.
[82]
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.
[83]
Radiotelescope research
In 1955, Bernard Burke and
Kenneth Franklin detected bursts of radio signals coming from Jupiter at 22.2 MHz.
[29]
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.
[84]
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.[85]
- Decimetric radio emission (with wavelengths measured in centimeters) was first observed by Frank Drake and Hein Hvatum in 1959.[29] 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.[86]
- Thermal radiation is produced by heat in the atmosphere of Jupiter.[29]
Exploration with space probes
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.
[87][88] 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
[89] which is comparable to the 9.7 km/s delta-v needed to reach low Earth orbit.
[90] Fortunately,
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.
[91]
Flyby missions
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[92] |
408,894 km |
| February 4, 2004[92] |
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.
[21][93]
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.
[15][21]
The next mission to encounter Jupiter, the
Ulysses solar probe, performed a flyby maneuver to attain a
polar orbit around the Sun. During this pass the spacecraft conducted studies on Jupiter's magnetosphere. Since
Ulysses has no cameras, no images were taken. A second flyby six years later was at a much greater distance.
[92]
Cassini views Jupiter and Io on January 1, 2001
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 spacecraft captured an
image of the moon
Himalia, but the resolution was too low to show surface details.
[94]
The
New Horizons probe, en route to
Pluto, flew by Jupiter for gravity assist. Its closest approach was on February 28, 2007.
[95]
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.
[96] Imaging of the Jovian system began September 4, 2006.
[97][98]
Galileo mission
Jupiter as seen by the space probe
Cassini.
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, 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. While the information gained about the Jovian system from
Galileo
was extensive, its originally designed capacity was limited by the
failed deployment of its high-gain radio transmitting antenna.
[99]
An atmospheric probe was released from the spacecraft in July 1995,
entering the planet's atmosphere on December 7. It parachuted through
150 km (93 mi) of the atmosphere, collected data for 57.6 minutes, and
was crushed by the pressure to which it was subjected by that time
(about 22 times Earth normal, at a temperature of 153 °C).
[100] It would have 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.
[99]
Future probes
NASA currently has a mission underway to study Jupiter in detail from a
polar orbit. Named
Juno, the spacecraft launched in August 2011, and will arrive in late 2016.
[101] The next planned mission to the Jovian system will be the
European Space Agency's
Jupiter Icy Moon Explorer (JUICE), due to launch in 2022.
[102]
Canceled missions
Because of the possibility of subsurface liquid oceans on Jupiter's
moons Europa, Ganymede and Callisto, there has been great interest in
studying the icy moons in detail. Funding difficulties have delayed
progress. NASA's
JIMO (
Jupiter Icy Moons Orbiter) was cancelled in 2005.
[103] A subsequent proposal for a joint
NASA/
ESA mission, called
EJSM/Laplace, was developed 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.
[104]
However by April 2011, ESA had formally ended the partnership 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.
[105]
Moons
Jupiter with the Galilean moons
Jupiter has 67
natural satellites.
[106]
Of these, 51 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 orbits of Io, Europa, and Ganymede, some of the largest satellites 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 large 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. The
tidal force from Jupiter, on the other hand, works to circularize their orbits.
[107]
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 |
3643 |
105 |
8.9×1022 |
120 |
421,700 |
110 |
1.77 |
7 |
| Europa |
jʊˈroʊpə |
3122 |
90 |
4.8×1022 |
65 |
671,034 |
175 |
3.55 |
13 |
| Ganymede |
ˈɡænimiːd |
5262 |
150 |
14.8×1022 |
200 |
1,070,412 |
280 |
7.15 |
26 |
| Callisto |
kəˈlɪstoʊ |
4821 |
140 |
10.8×1022 |
150 |
1,882,709 |
490 |
16.69 |
61 |
Classification of moons
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 believed 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 believed 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.
[108][109]
| 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[110] |
These four 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. |
| 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. |
| 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. |
| Pasiphaë group |
A dispersed and only vaguely distinct retrograde group that covers all the outermost moons. |
Interaction with the Solar System
Along with the Sun, the
gravitational influence of Jupiter has helped shape the Solar System. The orbits of most of the system's planets lie closer to Jupiter's
orbital plane than the Sun's
equatorial plane (
Mercury is the only planet that is closer to the Sun's equator in orbital tilt), the
Kirkwood gaps in the
asteroid belt are mostly caused by Jupiter, and the planet may have been responsible for the
Late Heavy Bombardment of the inner Solar System's history.
[111]
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.
[112] 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 believed 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.
[113]
Impacts
Jupiter has been called the Solar System's vacuum cleaner,
[115] 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.
[116]
It was thought that the planet served to partially shield the inner
system from cometary bombardment. 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 in roughly the same numbers that it accretes or ejects
them.
[117] This topic remains controversial among astronomers, as some believe it draws comets towards Earth from the
Kuiper belt while others believe that Jupiter protects Earth from the alleged
Oort cloud.
[118]
A 1997 survey of historical astronomical drawings suggested that the astronomer
Cassini
may have recorded an impact scar in 1690. The survey determined eight
other candidate observations had low or no possibilities of an impact.
[119] A
fireball was photographed by Voyager 1 during its Jupiter encounter in March 1979.
[120] 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.
[121][122]
On July 19, 2009, an
impact site was discovered at approximately 216 degrees longitude in System 2.
[123][124] 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.
[125]
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.
[126] Yet another fireball was seen on August 20, 2010.
[127]
On September 10, 2012, another fireball was detected.
[120][128]
Possibility of life
In 1953, the
Miller–Urey experiment
demonstrated that a combination of lightning and the chemical compounds
that existed in the atmosphere of a primordial Earth could form organic
compounds (including
amino acids)
that could serve as the building blocks of life. The simulated
atmosphere included water, methane, ammonia and molecular hydrogen; all
molecules still found in the atmosphere of Jupiter. The atmosphere of
Jupiter has a strong vertical air circulation, which would carry these
compounds down into the lower regions. The higher temperatures within
the interior of the atmosphere breaks down these chemicals, which would
hinder the formation of Earth-like life.
[129]
It is considered highly unlikely that there is any Earth-like life on
Jupiter, as there is only a small amount of water in the atmosphere and
any possible solid surface deep within Jupiter would be under
extraordinary pressures. In 1976, before the
Voyager missions, it was hypothesized that ammonia or
water-based
life could evolve in Jupiter's upper atmosphere. This hypothesis is
based 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.
[130][131]
The possible presence of underground oceans on some of Jupiter's
moons has led to speculation that the presence of life is more likely
there.
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.
[132] To the
Babylonians, this object represented their god
Marduk. They used the roughly 12-year orbit of this planet along the
ecliptic to define the
constellations of their
zodiac.
[21][133]
The Romans named it after
Jupiter (
Latin:
Iuppiter, Iūpiter) (also called Jove), the principal
god of
Roman mythology, whose name comes from the
Proto-Indo-European vocative compound *
Dyēu-pəter (nominative: *
Dyēus-pətēr, meaning "O Father Sky-God", or "O Father Day-God").
[134] 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.
[135]
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.
[136]
Jovian is the
adjectival form of Jupiter. The older adjectival form
jovial, employed by astrologers in the
Middle Ages, has come to mean "happy" or "merry," moods ascribed to
Jupiter's astrological influence.
[137]
The Chinese, Korean and Japanese referred to the planet as the "wood star" (
Chinese:
木星;
pinyin:
mùxīng), based on the Chinese
Five Elements.
[138] Chinese Taoism personified it as the
Fu star. The Greeks called it Φαέθων,
Phaethon, "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."
[139] In the
English language,
Thursday is derived from "Thor's day", with
Thor associated with the planet Jupiter in
Germanic mythology.
[140]
In the
Central Asian-Turkic myths,
Jupiter called as a "Erendiz/Erentüz", which means
"eren(?)+yultuz(star)". There are many theories about meaning of "eren".
Also, these peoples calculated 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.
[141]
