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The Great Red Spot is a persistent high-pressure region in the
atmosphere of Jupiter The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is mostly made of molecular hydrogen and helium in roughly Sun#Composition, solar proportions; other chemical compounds are present only in small amounts and in ...
, producing an
anticyclonic storm An anticyclonic storm is a storm with a high-pressure center, in which winds flow in the direction opposite to that of the flow above a region of low pressure. These storms can create powerful mesoanticylonic supercell storms that can generate ...
that is the largest in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. Located 22
degree Degree may refer to: As a unit of measurement * Degree (angle), a unit of angle measurement ** Degree of geographical latitude ** Degree of geographical longitude * Degree symbol (°), a notation used in science, engineering, and mathematics ...
s south of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
's
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
, it produces wind-speeds up to 432 km/h (268 mph). Observations from 1665 to 1713 are believed to be of the same storm; if this is correct, it has existed for at least years. It was next observed in September 1831, with 60 recorded observations between then and 1878, when continuous observations began.


Observation history

The Great Red Spot may have existed since before 1665, but it could also be the case that the present spot was first seen only in 1830, and well-studied only after a prominent apparition in 1879. The storm that was seen in the 17th century may have been different than the storm that exists today. A long gap separates its period of current study after 1830 from its 17th century discovery. Whether the original spot dissipated and reformed, whether it faded, or if the observational record was simply poor is unknown. For example, the first sighting of the Great Red Spot is often credited to
Robert Hooke Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...
, who described a spot on the planet in May 1664. However, it is likely that Hooke's spot was not only in another belt altogether (the North Equatorial Belt, as opposed to the current Great Red Spot's location in the South Equatorial Belt), but also that it was the shadow of a transiting moon, most likely that of
Callisto Callisto most commonly refers to: *Callisto (mythology), a nymph *Callisto (moon), a moon of Jupiter Callisto may also refer to: Art and entertainment *''Callisto series'', a sequence of novels by Lin Carter *''Callisto'', a novel by Torsten Kro ...
. Far more convincing is
Giovanni Cassini Giovanni Domenico Cassini, also known as Jean-Dominique Cassini (8 June 1625 – 14 September 1712) was an Italian (naturalised French) mathematician, astronomer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the C ...
's description of a "permanent spot" the following year. With fluctuations in visibility, Cassini's spot was observed from 1665 to 1713, but the 118-year observational gap makes the identity of the two spots inconclusive. The older spot's shorter observational history and slower motion than the modern spot makes it difficult to conclude that they are the same. A minor mystery concerns a Jovian spot depicted in a 1711 canvas by
Donato Creti Donato Creti (24 February 1671 – 31 January 1749) was an Italian painter of the Rococo period, active mostly in Bologna. Born in Cremona, he moved to Bologna, where he was a pupil of Lorenzo Pasinelli. He is described by Wittkower as the "Bol ...
, which is exhibited in the
Vatican Vatican may refer to: Vatican City, the city-state ruled by the pope in Rome, including St. Peter's Basilica, Sistine Chapel, Vatican Museum The Holy See * The Holy See, the governing body of the Catholic Church and sovereign entity recognized ...
.Hockey (1999), 40-1. Part of a series of panels in which different (magnified) heavenly bodies serve as backdrops for various
Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...
scenes, and all overseen by the astronomer
Eustachio Manfredi Eustachio Manfredi (20 September 1674 – 15 February 1739) was an Italian mathematician, astronomer and poet. Biography Eustachio Manfredi was born in Bologna on 20 September 1674. He attended Jesuit school, then studied at the University of ...
for accuracy, Creti's painting is the first known to depict the Great Red Spot as red (albeit raised to the Jovian Northern hemisphere due to an optical inversion inherent to the era's telescopes). No Jovian feature was explicitly described in writing as red before the late 19th century. The Great Red Spot has been observed since 5 September 1831. By 1879 over 60 observations were recorded. After it came into prominence in 1879, it has been under continuous observation. In the 21st century, the Great Red Spot has been observed to be shrinking in size. At the start of 2004, its longitudinal extent was approximately half that of a century earlier, when it reached a size of , about three times the diameter of Earth. At the present rate of reduction, it would become circular by 2040. It is not known how long the spot will last, or whether the change is a result of normal fluctuations. In 2019, the Great Red Spot began "flaking" at its edge, with fragments of the storm breaking off and dissipating. The shrinking and "flaking" fueled concern from some astronomers that the Great Red Spot could dissipate within 20 years. However, other astronomers believe that the apparent size of the Great Red Spot reflects its cloud coverage and not the size of the actual, underlying vortex, and they also believe that the flaking events can be explained by interactions with other cyclones or anticyclones, including incomplete absorptions of smaller systems; if this is the case, this would mean that the Great Red Spot is not in danger of dissipating. A smaller spot, designated Oval BA, formed in March 2000 from the merging of three white ovals, has turned reddish in color. Astronomers have named it the ''Little Red Spot'' or ''Red Jr.'' As of 5 June 2006, the Great Red Spot and Oval BA appeared to be approaching convergence. The storms pass each other about every two years but the passings of 2002 and 2004 were of little significance. Amy Simon-Miller, of the
Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
, predicted the storms would have their closest passing on 4 July 2006. She worked with
Imke de Pater Imke de Pater is a Dutch astronomer working at the University of California, Berkeley. She is known for her research on the large planets and led the team using the Keck Telescope to image the 1994 impact of the comet Comet Shoemaker–Levy 9 wit ...
and Phil Marcus of
UC Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of Californi ...
and a team of professional astronomers since April 2006 to study the storms using the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
; on 20 July 2006, the two storms were photographed passing each other by the
Gemini Observatory The Gemini Observatory is an astronomical observatory consisting of two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, which are located at two separate sites in Hawaii and Chile, respectively. The twin Gemini telescopes prov ...
without converging. In May 2008, a third storm turned red. The Great Red Spot should not be confused with the Great Dark Spot, a feature observed near the northern pole of Jupiter in 2000 with the ''
Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space research, space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, i ...
'' spacecraft. There is also a feature in the atmosphere of
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
also called the
Great Dark Spot The Great Dark Spot (also known as GDS-89, for Great Dark Spot, 1989) was one of a series of dark spots on Neptune similar in appearance to Jupiter's Great Red Spot. In 1989, GDS-89 was the first Great Dark Spot on Neptune to be observed by NASA's ...
. The latter feature was imaged by ''
Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on a ...
'' in 1989 and may have been an atmospheric hole rather than a storm. It was no longer present as of 1994, although a similar spot had appeared farther to the north.


Exploration

On 25 February 1979, when the ''
Voyager 1 ''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin ''Voyager 2'', ''Voya ...
'' spacecraft was from Jupiter, it transmitted the first detailed image of the Great Red Spot. Cloud details as small as across were visible. The colorful, wavy cloud pattern seen to the left (west) of the Red Spot is a region of extraordinarily complex and variable wave motion. The ''Juno'' spacecraft, which entered into a polar orbit around Jupiter in 2016, flew over the Great Red Spot upon its close approach to Jupiter on 11 July 2017, taking several images of the storm from a distance of about above the surface. Over the duration of the ''Juno'' mission, the spacecraft continued to study the composition and evolution of Jupiter's atmosphere, especially its Great Red Spot.


Structure

Jupiter's Great Red Spot rotates counterclockwise, with a period of about 4.5 Earth days or 11 Jovian days in 2008. Measuring in width as of 3 April 2017, Jupiter's Great Red Spot is 1.3 times the diameter of Earth. The cloud-tops of this storm are about above the surrounding cloud-tops.
Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
data has long indicated that the Great Red Spot is colder (and thus higher in altitude) than most of the other clouds on the planet. The upper atmosphere above the storm, however, has substantially higher temperatures than the rest of the planet. Acoustic (sound) waves rising from the turbulence of the storm below have been proposed as an explanation for the heating of this region. Careful tracking of atmospheric features revealed the Great Red Spot's counter-clockwise circulation as far back as 1966, observations dramatically confirmed by the first time-lapse movies from the ''Voyager'' fly-bys. The spot is confined by a modest eastward
jet stream Jet streams are fast flowing, narrow, meandering thermal wind, air currents in the Atmosphere of Earth, atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are west ...
to its south and a very strong westward one to its north. Though winds around the edge of the spot peak at about , currents inside it seem stagnant, with little inflow or outflow. The rotation period of the spot has decreased with time, perhaps as a direct result of its steady reduction in size. The Great Red Spot's
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
has been stable for the duration of good observational records, typically varying by about a degree. Its
longitude Longitude (, ) is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter l ...
, however, is subject to constant variation, including a 90-day longitudinal oscillation with an amplitude of ~1°. Because Jupiter does not rotate uniformly at all latitudes, astronomers have defined three different systems for defining the longitude. System II is used for latitudes of more than 10 degrees and was originally based on the average rotational period of the Great Red Spot of 9h 55m 42s. Despite this, however, the spot has "lapped" the planet in System II at least 10 times since the early nineteenth century. Its drift rate has changed dramatically over the years and has been linked to the brightness of the South Equatorial Belt and the presence or absence of a South Tropical Disturbance.


Internal depth and structure

Jupiter's Great Red Spot (GRS) is an elliptical shaped anticyclone, occurring at 22 degrees below the equator, in Jupiter's southern hemisphere. The largest
anticyclonic An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from abov ...
storm (~16,000 km) in our solar system, little is known about its internal depth and structure. Visible imaging and cloud-tracking from in-situ observation determined the velocity and vorticity of the GRS which is located in a thin anticyclonic ring at 70–85% of the radius and is located along Jupiter's fastest westward moving jet stream. During NASA's 2016
Juno Juno commonly refers to: *Juno (mythology), the Roman goddess of marriage and queen of the gods *Juno (film), ''Juno'' (film), 2007 Juno may also refer to: Arts, entertainment and media Fictional characters *Juno, in the film ''Jenny, Juno'' *Ju ...
mission, gravity signature and thermal infrareddata was obtained that offered insight into the structural dynamics and depth of the GRS. During July 2017, the Juno spacecraft conducted a second pass of the GRS to collect
Microwave Radiometer A microwave radiometer (MWR) is a radiometer that measures energy emitted at one millimeter-to-metre wavelengths (frequencies of 0.3–300 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermally- ...
(MWR) scans of the GRS to determine how far the GRS extended toward the surface of the condensed H2O layer. These MWR scans suggested that the GRS vertical depth extended to about 240 km below the cloud level, with an estimated drop in atmospheric pressure to 100 bar. Two methods of analysis that constrain the data collected were the Mascon approach which found a depth of ~290 km, and the Slepian approach showing wind extending to ~310 km. These methods, along with gravity signature MWR data suggest that the GRS zonal winds still increase at a rate of 50% the velocity of the viable cloud level, before the wind decay starts at lower levels, this rate of wind decay and Gravity data suggest the depth of the GRS is between 200 and 500 km.
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
and Cassini's thermal infrared imaging and
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
were conducted of the GRS during 1995–2008, in order to find evidence of thermal inhomogeneities with in the internal structure vortex of the GRS. Previous thermal infrared temperature maps from the Voyager, Galileo, and Cassini missions; suggested the GRS is a cold-core within a upwelling warmer annulus structure of an anticyclonic vortex, this data shows a gradient in the temperature of the GRS. To gain better understanding of Jupiter's atmospheric temperature, aerosol particle opacity, and ammonia gas composition from thermal-IR imaging, a direct correlation of the visible-cloud layers reactions, thermal gradient and compositional mapping to observational data collected over decades. During December 2000, high spatial resolution images from Galileo, of an atmospheric turbulent area to the northwest of the GRS, shows a thermal contrast between the warmest region of the anticyclone with regions to the east and west of the GRS. The vertical temperature of the structure of the GRS is constrained between the 100–600 mbar range, with the vertical temperature of the GRS core is approximately 400 mbar of pressure, being 1.0–1.5 K, much warmer than regions of the GRS to the east–west, and 3.0–3.5 K warmer than regions to the north–south of the structures edge. This structure is consistent with the data collected by the VISIR (VLT Mid-Infrared Imager Spectrometer on the ESO Very Large Telescope) imaging obtain in 2006, this data revealed that the GRS was physically present in a wide range of altitudes that occur within the 80 - 600 mbar pressure of the atmosphere and confirmers the thermal infrared mapping result. To develop a model of the internal structure of the GRS the Cassini mission Composite
Infrared Spectrometer Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...
(CIRS) and ground based spatial imaging mapped the composition of the
phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
aerosols (PH3, NH3 and para-hydroxybenzoic acid) within the anticyclonic circulation of the GRS. The imaging that was collected form the CIRS and ground-based imaging trace the vertical motion in the Jovian atmosphere by PH3 and NH3 spectra. The highest concentrations of PH3 and NH3 are found to the north of the GRS peripheral rotation and aided in determine the southward jet movement and shows data of an increase in altitude of the column of aerosols with ranging pressures of 200–500 mbar. However, the NH3 composition data shows that there is a major depletion of NH3 below the visible cloud layer at the southern peripheral ring of the GRS, this lower opacity is relative to a narrow band of atmospheric subsidence. The low mid-IR aerosol opacity along with; the temperature gradients, the altitude difference, and the vertical movement of the zonal winds are involved with the development and sustainability of the vorticity. The stronger atmospheric
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...
and compositional asymmetries of the GRS suggest that the structure exhibits a degree of tilt form the northern edge to the southern edge of the structure. The GRS depth and internal structure has been constant with changes over decades however there is still no logical reason why it is 200–500 km in depth, but the jet streams that supply the force that powers the GRS vortex are well below the structure base.


Color and composition

It is not known what causes the Great Red Spot's reddish color. Hypotheses supported by laboratory experiments suppose that it may be caused by chemical products created from the solar ultraviolet irradiation of
ammonium hydrosulfide Ammonium hydrosulfide is the chemical compound with the formula . Composition It is the salt derived from the ammonium cation and the hydrosulfide anion. The salt exists as colourless, water-soluble, micaceous crystals. On Earth the compound ...
and the organic compound
acetylene Acetylene (systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
, which produces a reddish material—likely complex organic compounds called
tholin Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
s. The high altitude of the compounds may also contribute to the coloring. The Great Red Spot varies greatly in hue, from almost brick-red to pale salmon or even white. The spot occasionally disappears, becoming evident only through the Red Spot Hollow, which is its location in the South Equatorial Belt (SEB). Its visibility is apparently coupled to the SEB; when the belt is bright white, the spot tends to be dark, and when it is dark, the spot is usually light. These periods when the spot is dark or light occur at irregular intervals; from 1947 to 1997, the spot was darkest in the periods 1961–1966, 1968–1975, 1989–1990, and 1992–1993.Beebe (1997), 38-41.


Mechanical dynamics

The reason the storm has continued to exist for centuries is that there is no planetary surface (only a mantle of
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
) to provide friction; circulating gas eddies persist for a very long time in the atmosphere because there is nothing to oppose their angular momentum. Research suggests that the storm produces extreme amounts of
acoustic wave Acoustic waves are a type of energy propagation through a medium by means of adiabatic loading and unloading. Important quantities for describing acoustic waves are acoustic pressure, particle velocity, particle displacement and acoustic intensit ...
s, owing to the turbulence of the storm. The acoustic waves travel vertically upwards to a height of above the storm where they break in the upper atmosphere, converting wave energy into heat. This creates a region of upper atmosphere that is —several hundred Kelvin warmer than the rest of the planet at this altitude. The effect is described as being like "crashing ..ocean waves on a beach".


Gallery

File:Winds in Jupiter’s Great Red Spot.jpg, Winds in Jupiter's Great Red Spot File:790106-0203 Voyager 58M to 31M reduced.gif, Time-lapse sequence from the approach of ''
Voyager 1 ''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin ''Voyager 2'', ''Voya ...
'' to Jupiter, showing the motion of atmospheric bands, and circulation of the Great Red Spot. ''NASA image''. File:Great red spot juno 20170712.jpg, Closeup of the Great Red Spot taken from about above it (July 11, 2017) File:Jupiter-Earth-Spot comparison.jpg, Approximate size comparison of Earth and the Great Red Spot. File:Jupiter’s Colourful Palette.tif, Jupiter's clouds taken on 27 June 2019 by Hubble's Wide Field Camera 3. File:PIA02863 - Jupiter surface motion animation.gif, Color animation of Jupiter's cloud motion and circulation of the Great Red Spot.


See also

*
Extraterrestrial vortex An extraterrestrial vortex is a vortex that occurs on planets and natural satellites other than Earth that have sufficient atmospheres. Most observed extraterrestrial vortices have been seen in large cyclones, or anticyclones. However, occasional ...
*
Great White Spot Saturn's Great White Spot in 2011. The Great White Spot, also known as Great White Oval, on Saturn, named by analogy to Jupiter's Great Red Spot, are periodic storms that are large enough to be visible from Earth by telescope by their character ...
, a similar storm on
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
*
Hypercane A hypercane is a hypothetical class of extreme tropical cyclone that could form if sea surface temperatures reached approximately , which is warmer than the warmest ocean temperature ever recorded. Such an increase could be caused by a large ast ...
* WISEP J190648.47+401106.8


References


Further reading

* * * * * *


External links

* * * * *
Video based on Juno's Perijove 7 overflight
by Seán Doran (se
album
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