J.
Theoretical models indicate that if Jupiter had much more mass than it does at present, the planet would shrink. For small changes in mass, the radiusIn classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
would not change appreciably, and above about (1.6 Jupiter masses) 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 dwarfBrown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
s around 50 Jupiter masses. This has led some astronomers to term it a "failed star", although it is unclear whether the processes involved in the formation of planets like Jupiter are similar to the processes involved in the formation of multiple star systemA star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...
s.
Although Jupiter would need to be about 75 times as massive to fuse hydrogen and become a starA star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
, the smallest red dwarfAccording to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
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 the planet is similar to the total solar radiation it receives. This additional heat radiation is generated by the Kelvin–Helmholtz mechanism through adiabaticIn thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which the net heat transfer to or from the working fluid is zero. Such a process can occur if the container of the system has thermally-insulated walls or the process happens in an extremely short time,...
contraction. This process results in the planet shrinking 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 coreThe planetary core consists of the innermost layer of a planet.The core may be composed of solid and liquid layers, while the cores of Mars and Venus are thought to be completely solid as they lack an internally generated magnetic field. In our solar system, core size can range from about 20% to...
with a mixture of elements, a surrounding layer of liquid metallic hydrogenMetallic hydrogen is a state of hydrogen which results when it is sufficiently compressed and undergoes a phase transition; it is an example of degenerate matter. Solid metallic hydrogen is predicted to consist of a crystal lattice of hydrogen nuclei , with a spacing which is significantly smaller...
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 rockyIn geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
, 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 the Earth's mass or roughly 3%–15% 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 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, 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 (J6) used to describe the planet's gravitational moment, Jupiter's equatorial radius, and its temperature at 1 bar pressure. The Juno missionJuno is a NASA New Frontiers mission to the planet Jupiter. Juno was launched from Cape Canaveral Air Force Station on August 5, 2011. The spacecraft is to be placed in a polar orbit to study the planet's composition, gravity field, magnetic field, and polar magnetosphere...
, which launched in August 2011, is expected to narrow down the value of these parameters, and thereby make progress on the problem of the core.
The core region is surrounded by dense metallic hydrogenMetallic hydrogen is a state of hydrogen which results when it is sufficiently compressed and undergoes a phase transition; it is an example of degenerate matter. Solid metallic hydrogen is predicted to consist of a crystal lattice of hydrogen nuclei , with a spacing which is significantly smaller...
, which extends outward to about 78 percent 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.
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 KThe kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
(see hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
). 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 kmKM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
, and as liquid in deeper layers. Physically, there is no clear boundary—gas smoothly becomes hotter and denser as one descends.
The temperature and pressure inside Jupiter increase steadily toward the core. At the phase transitionA phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....
region where hydrogen—heated beyond its critical point—becomes metallic, it is believed the temperature is 10,000 K and the pressure is 200 GPaThe pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
. The temperature at the core boundary is estimated to be 36,000 K and the interior pressure is roughly 3,000–4,500 GPa.
Atmosphere
Jupiter has the largest planetary atmosphere in the Solar System, spanning over 5000 km in altitude. As Jupiter has no surface, the base of its atmosphere is usually considered to be the point at which atmospheric pressure is equal to 10 bars, or ten times surface pressure on Earth.
Cloud layers
Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide. The clouds are located in the tropopauseThe tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
and are arranged into bands of different latitudeIn geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s, known as tropical regions. These are sub-divided into lighter-hued zones and darker belts. The interactions of these conflicting circulationAtmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....
patterns cause storms and turbulenceIn fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
. Wind speedWind speed, or wind velocity, is a fundamental atmospheric rate.Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications....
s 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 astronomers to give them identifying designations.
The cloud layer is only about 50 km 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 waterWater is the most abundant compound on Earth's surface, covering about 70%. In nature, it exists in liquid, solid, and gaseous states. It is in dynamic equilibrium between the liquid and gas states at standard temperature and pressure. At room temperature, it is a tasteless and odorless liquid,...
clouds underlying the ammonia layer, as evidenced by flashes of lightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
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. These electrical discharges can be up to a thousand times as powerful as lightning on the Earth. The water clouds can form 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 ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light from the Sun. The exact makeup remains uncertain, but the substances are believed to be phosphorus, sulfur or possibly hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s. These colorful compounds, known as chromophoreA chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...
s, mix with the warmer, lower deck of clouds. The zones are formed when rising convection cellA convection cell is a phenomenon of fluid dynamics that occurs in situations where there are density differences within a body of liquid or gas. The convection usually requires a gravitational field but in microgravity experiments, thermal convection has been observed without gravitational effects...
s form crystallizing ammonia that masks out these lower clouds from view.
Jupiter's low axial tiltIn astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
means that the poles constantly receive less solar radiation than at the planet's equatorial region. ConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
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
The best known feature of Jupiter is the Great Red Spot, a persistent anticyclonicAn anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
stormA storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
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. Mathematical modelA mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
s suggest that the storm is stable and may be a permanent feature of the planet. The storm is large enough to be visible through Earth-based telescopeA telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s with an apertureIn optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
of or larger.
The ovalIn technical drawing, an oval is a figure constructed from two pairs of arcs, with two different radii . The arcs are joined at a point, in which lines tangential to both joining arcs lie on the same line, thus making the joint smooth...
object rotatesA rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
counterclockwise, with a period of about six days. The Great Red Spot's dimensionIn physics and mathematics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it...
s are 24–40,000 km × 12–14,000 km. It is large enough to contain two or three planets of Earth's diameter. The maximum altitude of this storm is about 8 km above the surrounding cloudtops.
Storms such as this are common within the turbulent atmospheres of gas giantA gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
s. 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.
Planetary rings
Jupiter has a faint planetary ringA planetary ring is a ring of cosmic dust and other small particles orbiting around a planet in a flat disc-shaped region.The most notable planetary rings known in Earth's solar system are those around Saturn, but the other three gas giants of the solar system possess ring systems of their...
system composed of three main segments: an inner torusIn geometry, a torus is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle...
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 AdrasteaAdrastea , also known as ', is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in Voyager 2 probe photographs taken in 1979, making it the first natural satellite to be discovered from images taken by an interplanetary spacecraft, rather than...
and MetisMetis , also known as ', is the innermost moon of Jupiter. It was discovered in 1979 in images taken by Voyager 1, and was named in 1983 after the first wife of Zeus, 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 ThebeThebe also known as ', is the fourth of Jupiter's moons by distance from the planet. It was discovered by Stephen P. Synnott in images from the Voyager 1 space probe taken on March 5, 1979, while orbiting around Jupiter...
and AmaltheaAmalthea is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after Amalthea, a nymph in Greek mythology. It is also known as '....
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.
Magnetosphere
Jupiter's broad magnetic fieldA magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
is 14 times as strong as the Earth's, ranging from 4.2 gaussThe gauss, abbreviated as G, is the cgs unit of measurement of a magnetic field B , named after the German mathematician and physicist Carl Friedrich Gauss. One gauss is defined as one maxwell per square centimeter; it equals 1 tesla...
(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 sunspotSunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....
s). This field is believed to be generated by eddy currentEddy currents are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of...
s—swirling movements of conducting materials—within the metallic hydrogen core. The volcanoes on the moon IoIo ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
emit large amounts of sulfur dioxideSulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
forming a gas torus along the moon's orbit. The gas is ionized in the magnetosphere producing sulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
ionAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. They, together with hydrogen ions originating from the atmosphere of Jupiter, form a plasma sheetA current sheet is an electric current that is confined to a surface, rather than being spread through a volume of space. Current sheets feature in magnetohydrodynamics , the study of the behavior of electrically conductive fluids: if there is an electric current through part of the volume of such...
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 radioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
signature that produces bursts in the range of 0.6–30 MHzThe hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
.
At about 75 Jupiter radii from the planet, the interaction of the magnetosphere with the solar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
generates a bow shockA bow shock is the area between a magnetosphere and an ambient medium. For stars, this is typically the boundary between their stellar wind and the interstellar medium....
. Surrounding Jupiter's magnetosphere is a magnetopauseThe magnetopause is the abrupt boundary between a magnetosphere and the surrounding plasma. For planetary science, the magnetopause is the boundary between the planet’s magnetic field and the solar wind. The location of the magnetopause is determined by the balance between the pressure of the...
, located at the inner edge of a magnetosheathThe magnetosheath is the region of space between the magnetopause and the bow shock of a planet's magnetosphere. The regularly organized magnetic field generated by the planet becomes weak and irregular in the magnetosheath due to interaction with the incoming solar wind, and is incapable of fully...
—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 radioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
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 waveAn Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic wave.-Definition:An Alfvén wave in a plasma is a low-frequency travelling oscillation of the ions and the magnetic field...
s that carry ionized matter into the polar regions of Jupiter. As a result, radio waves are generated through a cyclotronIn technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
maser mechanismAn astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum...
, 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.
Orbit and rotation
Jupiter is the only planet that has a center of massIn physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
with the Sun that 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 from the Earth to the Sun, or 5.2 AUAn astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
) and it completes an orbit every 11.86 years. This is two-fifths the orbital period of SaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
, forming a 5:2 orbital resonanceIn celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
between the two largest planets in the Solar System. The elliptical orbit of Jupiter is inclined 1.31° compared to the Earth. Because of an eccentricityThe orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
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 tiltIn astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
of Jupiter is relatively small: only 3.13°. As a result this planet does not experience significant seasonA season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...
al changes, in contrast to Earth and Mars for example.
Jupiter's rotationA rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A 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 bulgeAn equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the centrifugal force of its rotation. A rotating body tends to form an oblate spheroid rather than a sphere...
easily seen through an Earth-based amateur telescopeA telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
. This rotation requires a centripetal acceleration at the equator of about 1.67 m/s2, compared to the equatorial surface gravity of 24.79 m/s2; thus the net acceleration felt at the equatorial surface is only about 23.12 m/s2. The planet is shaped as an oblate spheroid, meaning that the diameterIn geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
across its equatorAn equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
is longer than the diameter measured between its poles. On Jupiter, the equatorial diameter is 9275 km longer than the diameter measured through the poles.
Because Jupiter is not a solid body, its upper atmosphere undergoes differential rotationDifferential rotation is seen when different parts of a rotating object move with different angular velocities at different latitudes and/or depths of the body and/or in time. This indicates that the object is not solid. In fluid objects, such as accretion disks, this leads to shearing...
. The rotation of Jupiter's polarEarth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...
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 astronomersRadio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
, and corresponds to the rotation of the planet's magnetosphereA magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
; its period is Jupiter's official rotation.
Observation
Jupiter is usually the fourth brightest object in the sky (after the Sun, the MoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
and VenusVenus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
); at times Mars appears brighter than Jupiter. Depending on Jupiter's position with respect to the EarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, it can vary in visual magnitude from as bright as −2.9 at oppositionIn positional astronomy, two celestial bodies are said to be in opposition when they are on opposite sides of the sky, viewed from a given place . In particular, two planets are in opposition to each other when their ecliptic longitudes differ by 180°.The astronomical symbol for opposition is ☍...
down to −1.6 during conjunction with the Sun. The angular diameterThe angular diameter or apparent size of an object as seen from a given position is the “visual diameter” of the object measured as an angle. In the vision sciences it is called the visual angle. The visual diameter is the diameter of the perspective projection of the object on a plane through its...
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. As Jupiter approaches perihelionAn apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
in March 2011, there was a favorable opposition in September 2010.
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 motionApparent retrograde motion is the motion of a planetary body in a direction opposite to that of other bodies within its system as observed from a particular vantage point...
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 signAstrological signs represent twelve equal segments or divisions of the zodiac. According to astrology, celestial phenomena reflect or govern human activity on the principle of "as above, so below", so that the twelve signs are held to represent twelve basic personality types or characteristic modes...
s of the zodiacIn astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
, and may have been the historical origin of the signs. 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 anglePhase angle in astronomical observations is the angle between the light incident onto an observed object and the light reflected from the object...
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.
Pre-telescopic research
The observation of Jupiter dates back to the Babylonian astronomers of the 7th or 8th century BCE. The Chinese historian of astronomy, Xi ZezongXi Zezong was a Chinese astronomical historian. He is best known for his finding in Ancient Chinese history of the reference to Ganymede being visible to the human eye by ancient astronomer Gan De, before it was officially recognised by the west...
, has claimed that Gan DeGan De was a Chinese astronomer/astrologer born in the State of Qi also known as the Lord Gan . Along with Shi Shen, he is believed to be the first in history known by name to compile a star catalogue, preceded by the anonymous authors of the early Babylonian star catalogues and followed by the...
, a Chinese astronomerAstronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...
, made the discovery of one of Jupiter's moons in 362 BCE with the unaided eye. If accurate, this would predate Galileo's discovery by nearly two millennia.
In his 2nd century work the AlmagestThe Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...
, 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.
In 499, AryabhataAryabhata was the first in the line of great mathematician-astronomers from the classical age of Indian mathematics and Indian astronomy...
, a mathematicianA mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....
-astronomerAn astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
from the classical age of Indian mathematicsIndian mathematics emerged in the Indian subcontinent from 1200 BCE until the end of the 18th century. In the classical period of Indian mathematics , important contributions were made by scholars like Aryabhata, Brahmagupta, and Bhaskara II. The decimal number system in use today was first...
and astronomy, also used a geocentric model to estimate Jupiter's period as 4332.2722 days, or 11.86 years.
Ground-based telescope research
In 1610, Galileo GalileiGalileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
discovered the four largest moonsA natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
of Jupiter—Io, Europa, Ganymede and CallistoCallisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
(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 motionCelestial mechanics is the branch of astronomy that deals with the motions of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics is a subfield which focuses on...
not apparently centered on the Earth. It was a major point in favor of Copernicus'Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....
heliocentricHeliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...
theory of the motions of the planets; Galileo's outspoken support of the Copernican theory placed him under the threat of the InquisitionThe Inquisition, Inquisitio Haereticae Pravitatis , was the "fight against heretics" by several institutions within the justice-system of the Roman Catholic Church. It started in the 12th century, with the introduction of torture in the persecution of heresy...
.
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. In 1690 Cassini noticed that the atmosphere undergoes differential rotationDifferential rotation is seen when different parts of a rotating object move with different angular velocities at different latitudes and/or depths of the body and/or in time. This indicates that the object is not solid. In fluid objects, such as accretion disks, this leads to shearing...
.
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 HookeRobert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
and in 1665 by Giovanni CassiniThis article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...
, 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 BorelliGiovanni Alfonso Borelli was a Renaissance Italian physiologist, physicist, and mathematician. He contributed to the modern principle of scientific investigation by continuing Galileo's custom of testing hypotheses against observation...
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), and this timing discrepancy was used to estimate the speed of lightThe speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
.
In 1892, E. E. Barnard observed a fifth satellite of Jupiter with the 36 inches (91.4 cm) refractor at Lick ObservatoryThe Lick Observatory is an astronomical observatory, owned and operated by the University of California. It is situated on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, USA...
in CaliforniaCalifornia is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. The discovery of this relatively small object, a testament to his keen eyesight, quickly made him famous. The moon was later named AmaltheaAmalthea is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after Amalthea, a nymph in Greek mythology. It is also known as '....
. It was the last planetary moon to be discovered directly by visual observation. An additional eight satellites were subsequently discovered before the flyby of the Voyager 1The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...
probe in 1979.
In 1932, Rupert WildtRupert Wildt was a German-American astronomer.He was born in Munich, Germany, and grew up in that country during World War I and its aftermath. In 1927 he was awarded a Ph.D. from the University of Berlin...
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 FranklinKenneth Linn Franklin was an American astronomer and educator. Franklin was the chief scientist at the Hayden Planetarium from 1956 to 1984 and was co-credited with discovering radio waves originating on Jupiter, the first detection of signals from another planet...
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
Frank Donald Drake PhD is an American astronomer and astrophysicist. He is most notable as one of the pioneers in the search for extraterrestrial intelligence, including the founding of SETI, mounting the first observational attempts at detecting extraterrestrial communications in 1961 in Project...
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 radiationCyclotron radiation is electromagnetic radiation emitted by moving charged particles deflected by a magnetic field. The Lorentz force on the particles acts perpendicular to both the magnetic field lines and the particles' motion through them, creating an acceleration of charged particles that...
from electrons that are accelerated in Jupiter's magnetic field.
- Thermal radiation is produced by heat in the atmosphere of Jupiter.
Exploration with space probes
Since 1973 a number of automated spacecraft have visited Jupiter, most notably the Pioneer 10Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
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 energyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
, which is described by the net change in velocity of the spacecraft, or delta-vIn astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....
. Entering a Hohmann transfer orbitIn orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits, typically both in the same plane....
from Earth to Jupiter from low earth orbitA low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
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. Fortunately, gravity assistsIn orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
through planetary flybysIn orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...
can be used to reduce the energy required to reach Jupiter, albeit at the cost of a significantly longer flight duration.
Flyby missions
Flyby missions
| Spacecraft |
Closest
approach |
Distance |
Pioneer 10Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
|
December 3, 1973 |
130,000 km |
Pioneer 11Pioneer 11 is a 259-kilogram robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere...
|
December 4, 1974 |
34,000 km |
Voyager 1The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...
|
March 5, 1979 |
349,000 km |
Voyager 2The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
|
July 9, 1979 |
570,000 km |
UlyssesUlysses is a decommissioned robotic space probe that was designed to study the Sun as a joint venture of NASA and the European Space Agency . The spacecraft was originally named Odysseus, because of its lengthy and indirect trajectory to near Solar distance...
|
February 8, 1992 |
408,894 km |
| February 4, 2004 |
120,000,000 km |
| Cassini |
December 30, 2000 |
10,000,000 km |
New HorizonsNew Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
|
February 28, 2007 |
2,304,535 km |
The Pioneer program is a series of United States unmanned space missions that was designed for planetary exploration. There were a number of such missions in the program, but the most notable were Pioneer 10 and Pioneer 11, which explored the outer planets and left the solar system...
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. Occultations of the radio signals by the planet resulted in better measurements of Jupiter's diameter and the amount of polar flattening.
Six years later, the VoyagerThe Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
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, 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.
In 2000, the Cassini probe, en route to SaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.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 HimaliaHimalia is the largest irregular satellite of Jupiter, the sixth largest overall in size, and the fifth largest in mass. It was discovered by Charles Dillon Perrine at the Lick Observatory on 3 December 1904 and is named after the nymph Himalia, who bore three sons of Zeus .- Discovery...
, but the resolution was too low to show surface details.
The New HorizonsNew Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
probe, en route to PlutoPluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
, flew by Jupiter for gravity assist. 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 HimaliaHimalia is the largest irregular satellite of Jupiter, the sixth largest overall in size, and the fifth largest in mass. It was discovered by Charles Dillon Perrine at the Lick Observatory on 3 December 1904 and is named after the nymph Himalia, who bore three sons of Zeus .- Discovery...
and ElaraElara is a prograde irregular satellite of Jupiter. It was discovered by Charles Dillon Perrine at Lick Observatory in 1905. It is the eighth largest moon of Jupiter and is named after the mother by Zeus of the giant Tityus....
. Imaging of the Jovian system began September 4, 2006.
Galileo mission
So far the only spacecraft to orbit Jupiter is the GalileoGalileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...
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 AmaltheaAmalthea is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after Amalthea, a nymph in Greek mythology. It is also known as '....
. The spacecraft also witnessed the impact of Comet Shoemaker-Levy 9Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...
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.
An atmospheric probe was released from the spacecraft in July 1995, entering the planet's atmosphere on December 7. It parachuted through 150 km 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). 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.
Future probes and canceled missions
NASA currently has a mission underway to study Jupiter in detail from a polar orbitA polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...
. Named JunoJuno is a NASA New Frontiers mission to the planet Jupiter. Juno was launched from Cape Canaveral Air Force Station on August 5, 2011. The spacecraft is to be placed in a polar orbit to study the planet's composition, gravity field, magnetic field, and polar magnetosphere...
, the spacecraft launched in August 2011, and will arrive in late 2016.
The Europa Jupiter System MissionThe Europa Jupiter System Mission – Laplace was a proposed joint NASA/ESA unmanned space mission slated to launch around 2020 for the in-depth exploration of Jupiter's moons with a focus on Europa, Ganymede and Jupiter's magnetosphere...
(EJSM) is a joint NASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
/ESA proposal for exploration of Jupiter and its moons. In February 2009 it was announced that ESA/NASA had given this mission priority ahead of the Titan Saturn System MissionTitan Saturn System Mission was a joint NASA/ESA proposal for an exploration of Saturn and its moons Titan and Enceladus, where many complex phenomena have been revealed by the recent Cassini–Huygens mission...
. ESA's contribution will still face funding competition from other ESA projects. Launch date will be around 2020. EJSM consists of the NASA-led Jupiter Europa OrbiterAs a part of the Europa Jupiter System Mission , the Jupiter Europa Orbiter is a proposed orbiter probe slated for lift-off in 2020 and planned for detailed studies of Jupiter's moons Europa and Io as well as the Jovian magnetosphere...
, and the ESA-led Jupiter Ganymede OrbiterAs a part of the international Europa Jupiter System Mission , the Jupiter Ganymede Orbiter is a proposed orbiter probe by the ESA slated for lift-off in 2020. Plans for the mission include detailed studies of Jupiter's moons Ganymede and Callisto as well as the Jovian magnetosphere.-See...
.
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 JIMOThe Jupiter Icy Moons Orbiter was a proposed spacecraft designed to explore the icy moons of Jupiter. The main target was Europa, the suspected ocean of which is one of the places where simple alien life is a possibility in our solar system...
(Jupiter Icy Moons Orbiter) was cancelled in 2005. A European Jovian Europa OrbiterThe Jovian Europa Orbiter was a feasibility study by the European Space Agency for a mission to Jupiter's moon Europa. JEO would be capable of collecting information about Europa by orbiting it, and would correspond with the Jovian Relay Spacecraft and the Jovian Minisat Explorer .The Jovian...
mission was also studied. These missions were superseded by the Europa Jupiter System Mission (EJSM).
Moons
Jupiter has 64 named natural satelliteA natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
s. Of these, 47 are less than 10 kilometres in diameter and have only been discovered since 1975. The four largest moons, known as the "Galilean moonsThe Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...
", 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 forceThe tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force per unit mass exerted on one body by a second body is not constant across its diameter, the side nearest to the second being more attracted by it than the side...
from Jupiter, on the other hand, works to circularize their orbits.
The eccentricityThe orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
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 frictionFriction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of 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 MoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
|
| Name |
IPA |
Diameter |
Mass |
Orbital radius |
Orbital period |
| km |
% |
kg |
% |
km |
% |
days |
% |
IoIo ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
|ˈaɪ.oʊ |
3643 |
105 |
8.9×1022 |
120 |
421,700 |
110 |
1.77 |
7 |
EuropaEuropa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
|
jʊˈroʊpə |
3122 |
90 |
4.8×1022 |
65 |
671,034 |
175 |
3.55 |
13 |
GanymedeGanymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...
|ˈɡænimiːd |
5262 |
150 |
14.8×1022 |
200 |
1,070,412 |
280 |
7.15 |
26 |
CallistoCallisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
|
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 elementsOrbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used...
. 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.
| 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 The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...
|
These four moons, discovered by Galileo GalileiGalileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
and by Simon MariusSimon Marius was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but he spent most of his life in the city of Ansbach....
in parallel, orbit between 400,000 and 2,000,000 km, and include some of the largest moons in the Solar System. |
| Irregular moons |
ThemistoThemisto , also known as ', is a small prograde irregular satellite of Jupiter. It was discovered in 1975, lost, and then rediscovered in 2000.- Discovery and naming :...
|
This is a single moon belonging to a group of its own, orbiting halfway between the Galilean moons and the Himalia group. |
| Himalia group The Himalia group is a group of prograde irregular satellites of Jupiter that follow similar orbits to Himalia and are thought to have a common origin.The known members of the group are :* Leda...
|
A tightly clustered group of moons with orbits around 11,000,000–12,000,000 km from Jupiter. |
| Carpo Carpo , also ', is a natural satellite of Jupiter. It was discovered by a team of astronomers from the University of Hawaii led by Scott S...
|
Another isolated case; at the inner edge of the Ananke group, it orbits Jupiter in prograde direction. |
Ananke groupThe Ananke group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Ananke and are thought to have a common origin....
|
This retrograde orbit group has rather indistinct borders, averaging 21,276,000 km from Jupiter with an average inclination of 149 degrees. |
Carme groupThe Carme group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Carme and are thought to have a common origin....
|
A fairly distinct retrograde group that averages 23,404,000 km from Jupiter with an average inclination of 165 degrees. |
Pasiphaë groupThe Pasiphaë group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Pasiphaë and are thought to have a common origin....
|
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 planeAll of the planets, comets, and asteroids in the solar system are in orbit around the Sun. All of those orbits line up with each other making a semi-flat disk called the orbital plane. The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded...
than the Sun's equatorial planeThe celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space...
(MercuryMercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
is the only planet that is closer to the Sun's equator in orbital tilt), the Kirkwood gapA Kirkwood gap is a gap or dip in the distribution of main-belt asteroids with semi-major axis , as seen in the histogram below...
s in the asteroid beltThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
are mostly caused by Jupiter, and the planet may have been responsible for the Late Heavy BombardmentThe Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
of the inner Solar System's history.
Along with its moons, Jupiter's gravitational field controls numerous asteroidAsteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s that have settled into the regions of the Lagrangian pointThe Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
s preceding and following Jupiter in its orbit around the sun. These are known as the Trojan asteroidThe Jupiter Trojans, commonly called Trojans or Trojan asteroids, are a large group of objects that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each Trojan librates around one of the planet's two Lagrangian points of stability, and , that respectively lie 60° ahead...
s, and are divided into Greek and Trojan "camps" to commemorate the IliadThe Iliad is an epic poem in dactylic hexameters, traditionally attributed to Homer. Set during the Trojan War, the ten-year siege of the city of Troy by a coalition of Greek states, it tells of the battles and events during the weeks of a quarrel between King Agamemnon and the warrior Achilles...
. The first of these, 588 Achilles588 Achilles is an asteroid discovered on February 22, 1906, by the German astronomer Max Wolf. It was the first of the trojan asteroids to be discovered, and is named after Achilles, the fictional hero from the Iliad. It orbits in the Lagrangian point of the Sun-Jupiter system...
, was discovered by Max WolfMaximilian Franz Joseph Cornelius Wolf was a German astronomer and a pioneer in the field of astrophotography...
in 1906; since then more than two thousand have been discovered. The largest is 624 Hektor624 Hektor is the largest Jupiter Trojan. It was discovered in 1907 by August Kopff.Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, , called the 'Greek' node after one of the two sides in the legendary Trojan War...
.
Most short-period comets belong to the Jupiter family—defined as comets with semi-major axesThe major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
smaller than Jupiter's. Jupiter family comets are believed to form in the Kuiper beltThe Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
outside the orbit of Neptune. During close encounters with Jupiter their orbits are perturbPerturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....
ed into a smaller period and then circularized by regular gravitational interaction with the Sun and Jupiter.
Impacts
Jupiter has been called the Solar System's vacuum cleaner, because of its immense gravity wellA gravity well or gravitational well is a conceptual model of the gravitational field surrounding a body in space. The more massive the body the deeper and more extensive the gravity well associated with it. The Sun has a far-reaching and deep gravity well. Asteroids and small moons have much...
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. 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. This topic remains controversial among astronomers, as some believe it draws comets towards Earth from the Kuiper beltThe Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
while others believe that Jupiter protects Earth from the alleged Oort cloudThe Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
.
A 1997 survey of historical astronomical drawings suggested that the astronomer CassiniThis article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...
may have recorded an impact scar in 1690. The survey determined eight other candidate observations had low or no possibilities of an impact. During the period July 16, 1994, to July 22, 1994, over 20 fragments from the cometA comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
Shoemaker–Levy 9 (SL9, formally designated D/1993 F2) collided with Jupiter's southern hemisphereThe Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
, 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 siteThe 2009 Jupiter impact event, occasionally referred to as the Wesley impact, was a July 2009 impact on Jupiter that caused a black spot in the planet's atmosphere. The spot was similar in area to the planet's Little Red Spot, approximately the size of the Pacific Ocean...
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.
Another impact eventThe 2010 Jupiter impact event was a bolide impact event on Jupiter by an object estimated to be about 8–13 meters in diameter. The impactor may have been an asteroid, comet, centaur, extinct comet, or temporary satellite capture.-Observation:...
, smaller than the previous observed impacts, was detected on June 3, 2010, by Anthony Wesley, an amateur astronomerAmateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
in Australia, and was later discovered to have been captured on video by another amateur astronomer in the PhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
.
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 acidAmino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s) 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.
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 VoyagerThe Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
missions, it was hypothesized that ammonia or waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
-based life could evolve in Jupiter's upper atmosphere. This hypothesis is based on the ecology of terrestrial seas which have simple photosyntheticPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
planktonPlankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
at the top level, fishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
at lower levels feeding on these creatures, and marine predators which hunt the fish.
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.
Ancient mythology
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 BabylonBabylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...
ians, this object represented their god MardukMarduk was the Babylonian name of a late-generation god from ancient Mesopotamia and patron deity of the city of Babylon, who, when Babylon became the political center of the Euphrates valley in the time of Hammurabi , started to...
. They used the roughly 12-year orbit of this planet along the eclipticThe ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
to define the constellationIn modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
s of their zodiacIn astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
.
The Romans named it after JupiterIn ancient Roman religion and myth, Jupiter or Jove is the king of the gods, and the god of the sky and thunder. He is the equivalent of Zeus in the Greek pantheon....
(also called Jove), the principal godA god, as a male deity, contrasts with female deities, or "goddesses". While the term 'goddess' specifically refers to a female deity, the plural 'gods' can be applied to all gods collectively, regardless of gender....
of Roman mythologyRoman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...
, whose name comes from the Proto-Indo-EuropeanThe Proto-Indo-European language is the reconstructed common ancestor of the Indo-European languages, spoken by the Proto-Indo-Europeans...
vocative compound *Dyēu-pəter (nominative: *Dyēus*Dyēus is the reconstructed chief deity of the Proto-Indo-European pantheon. He was the god of the daylight sky, and his position may have mirrored the position of the patriarch or monarch in society....
-pətēr, meaning "O Father Sky-God", or "O Father Day-God").
The astronomical symbol for the planet, , is a stylized representation of the god's lightning bolt. The original Greek deity, ZeusIn the ancient Greek religion, Zeus was the "Father of Gods and men" who ruled the Olympians of Mount Olympus as a father ruled the family. He was the god of sky and thunder in Greek mythology. His Roman counterpart is Jupiter and his Etruscan counterpart is Tinia.Zeus was the child of Cronus...
, adopted by Romans, supplies the root zeno-, used to form some Jupiter-related words, such as zenographic.
Jovian is the adjectivalIn grammar, an adjective is a 'describing' word; the main syntactic role of which is to qualify a noun or noun phrase, giving more information about the object signified....
form of Jupiter. The older adjectival form jovial, employed by astrologers in the Middle AgesThe Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...
, has come to mean "happy" or "merry," moods ascribed to Jupiter's astrological influence.
The Chinese, Korean and Japanese referred to the planet as the wood star, , based on the Chinese Five ElementsThe Wu Xing, also known as the Five Phases, the Five Agents, the Five Movements, and the Five Steps/Stages, are chiefly an ancient mnemonic device, in many traditional Chinese fields....
. The Greeks called it Φαέθων, Phaethon, "blazing." In Vedic AstrologyHindu astrology , also Jyotish or Jyotisha, from Sanskrit , from "light, heavenly body") is the ancient Indian system of astronomy and astrology...
, Hindu astrologers named the planet after BrihaspatiBṛhaspati also known as Brahmanaspati and Deva-guru , is the name of a Vedic deity...
, the religious teacher of the gods, and often called it "GuruA guru is one who is regarded as having great knowledge, wisdom, and authority in a certain area, and who uses it to guide others . Other forms of manifestation of this principle can include parents, school teachers, non-human objects and even one's own intellectual discipline, if the...
", which literally means the "Heavy One." In the English languageEnglish is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
, ThursdayThursday is the fourth day of the week according to the ISO 8601 international standard adopted in most western countries. In countries that use the Sunday-first convention and in the Judeo-Christian calendar it is the fifth day of the week. It falls between Wednesday and Friday...
is derived from "Thor's day", with ThorIn Norse mythology, Thor is a hammer-wielding god associated with thunder, lightning, storms, oak trees, strength, the protection of mankind, and also hallowing, healing, and fertility...
associated with the planet Jupiter in Germanic mythologyGermanic paganism refers to the theology and religious practices of the Germanic peoples of north-western Europe from the Iron Age until their Christianization during the Medieval period...
.
See also
- Exploration of Jupiter
The exploration of Jupiter has to date been conducted via close observations by automated spacecraft. It began with the arrival of Pioneer 10 into the Jovian system in 1973, and, , has continued with seven further spacecraft missions...
- Pioneer 10 space probe to Jupiter
Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
- Space exploration
Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....
- Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
(Many are larger than Jupiter.)
- Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
- Juno (spacecraft)
Juno is a NASA New Frontiers mission to the planet Jupiter. Juno was launched from Cape Canaveral Air Force Station on August 5, 2011. The spacecraft is to be placed in a polar orbit to study the planet's composition, gravity field, magnetic field, and polar magnetosphere...
- Jupiter in fiction
Jupiter, the largest planet in the solar system, is a popular backdrop for science fiction stories and films. Although Jupiter is now known to have no solid surface one could land on, and has long been known to have an atmosphere, temperature, and high gravity hostile to human life, some earlier...
- Jovian-Plutonian gravitational effect
The Jovian–Plutonian gravitational effect, a hoax phenomenon stated to cause a noticeable short-term reduction in gravity on Earth, was an invention for April Fools' Day by the English astronomer Patrick Moore broadcast on BBC Radio 2 on 1 April 1976....
External links
—A simulation of the 62 Jovian moons.