Great Red Spot
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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 solar proportions; other chemical compounds are present only in small amounts and include methane, a ...
, producing an anticyclonic storm 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 "Sola ...
. It is the most recognizable feature on Jupiter, owing to its red-orange color whose origin is still unknown. Located 22 degrees 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 Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
's
equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
, it produces wind-speeds up to . It was first observed in September 1831, with 60 recorded observations between then and 1878, when continuous observations began. A similar spot was observed from 1665 to 1713; if this is the same storm, it has existed for at least years, but a study from 2024 suggests this is not the case.


Observation history


First observations

The Great Red Spot may have existed before 1665, but it could be that the present spot was first seen only in 1830, and was well studied only after a prominent appearance in 1879. The storm that was seen in the 17th century may have been different from the storm that exists today. A long gap separates its period of current study after 1830 from the 17th century discovery. It is unknown whether the original spot dissipated and reformed, whether it faded away, or whether observers simply failed to study and record it. The first sighting of the Great Red Spot is often credited to
Robert Hooke Robert Hooke (; 18 July 16353 March 1703) was an English polymath who was active as a physicist ("natural philosopher"), astronomer, geologist, meteorologist, and architect. He is credited as one of the first scientists to investigate living ...
, 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 in the South Equatorial Belt), but also that it was in the shadow of a transiting moon, most likely
Callisto CALLISTO (''Cooperative Action Leading to Launcher Innovation in Stage Toss-back Operations'') is a reusable VTVL Prototype, demonstrator propelled by a small 40 kN Japanese LOX-LH2 rocket engine. It is being developed jointly by the CNES, French ...
. In the following year,
Giovanni Cassini Giovanni Domenico Cassini (8 June 1625 – 14 September 1712) was an Italian-French mathematician, astronomer, astrologer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the County of Nice, part of the Savoyard sta ...
describes a "a permanent potwhich was often seen to return in the same place with the same size and shape", calculating its rotation period to be . With fluctuations in visibility, Cassini's spot was observed from 1665 to 1713, but the 48-year observational gap makes the identity of the two spots inconclusive. Because of the older spot's shorter observational history and slower motion than the modern spot, it is difficult to conclude that they are the same. A minor mystery concerns a Jovian spot depicted in a 1711 canvas by Donato Creti, which is exhibited in the
Vatican Vatican may refer to: Geography * Vatican City, an independent city-state surrounded by Rome, Italy * Vatican Hill, in Rome, namesake of Vatican City * Ager Vaticanus, an alluvial plain in Rome * Vatican, an unincorporated community in the ...
. 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, a Romance ethnic group related to or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance languag ...
scenes, and all overseen by the astronomer Eustachio Manfredi for accuracy, Creti's painting is the first known depiction of a large spot on Jupiter 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 frequently observed since 5 September 1831, with over 60 observations recorded by 1879, when it came into popular prominence. Since then, it has been under continuous observation. A 2024 study of historical observations suggests that the "permanent spot" observed from 1665 to 1713 may not be the same as the modern Great Red Spot observed since 1831. It is suggested that the original spot disappeared, and later another spot formed, which is the one seen today.


Late 20th and 21st centuries

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 the interstellar medium, interstellar space beyond the Sun's heliosphere. It was launched 16 days afte ...
'' 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. In the 21st century, the major diameter of the Great Red Spot has been observed to be shrinking. In 2004 its length was about 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 will become circular by 2040. It is not known how long the spot will last, or whether the change is a result of periodic fluctuations. In 2019, the spot began "flaking" at its edge, with fragments of the storm spinning off and dissipating. The shrinking and "flaking" fueled speculation from some astronomers that the spot could dissipate within decades. However, other astronomers believe the apparent size of the spot reflects its cloud coverage and not the size of the underlying vortex, and also that the flaking events can be explained by interactions with other cyclones or anticyclones, including incomplete absorptions of smaller systems; this might mean that the Great Red Spot is not in danger of dissipating. A smaller spot, designated Oval BA, which 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 ...
, predicted the storms would have their closest passing on 4 July 2006. She worked with Imke de Pater and Phil Marcus of
UC Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a public land-grant research university in Berkeley, California, United States. Founded in 1868 and named after the Anglo-Irish philosopher George Berkele ...
as well as a team of professional astronomers beginning in April 2006 to study the storms using the
Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
; on 20 July 2006, the two storms were photographed passing each other by the
Gemini Observatory The Gemini Observatory comprises two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, situated in Hawaii and Chile, respectively. These twin telescopes offer extensive coverage of the northern and southern skies and rank among ...
without converging. In May 2008, a third storm turned red. 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. 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 and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...
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' ...
. The latter feature was imaged by ''
Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory towards the gas giants (Jupiter and Saturn) and enabled further encounters with the ice giants (Uranus and ...
'' in 1989 and may have been an atmospheric hole rather than a storm. It disappeared by 1994, although a similar spot had appeared farther to the north.


Mechanical dynamics

Jupiter's Great Red Spot rotates counterclockwise, with a period of about 4.5 Earth days, or 11 Jovian days, as of 2008. Measuring in width as of 3 April 2017, the Great Red Spot is 1.3 times the diameter of Earth. The cloud-tops of this storm are about above the surrounding cloud-tops. The storm has continued for centuries because there is no planetary surface (only a mantle of
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
) to cause friction; circulating atmospheric eddies persist because there is nothing to oppose their angular momentum.
Infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
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 waves rising from the turbulence of the storm below have been proposed as an explanation for the heating of this region. The acoustic waves travel vertically up 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 kelvins warmer than the rest of the planet at this altitude. The effect is described as like "crashing ..ocean waves on a beach". Careful tracking of atmospheric features revealed the Great Red Spot's counterclockwise 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 thermal wind, air currents in the Earth's Atmosphere of Earth, atmosphere. The main jet streams are located near the altitude of the tropopause and are westerly winds, flowing west to east around the gl ...
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 of the spot has slowed with time, perhaps as a direct result of its steady reduction in size. The Great Red Spot's
latitude In geography, latitude is a geographic coordinate system, geographic 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 t ...
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 lett ...
, however, is subject to constant variation, including a 90-day longitudinal oscillation with an amplitude of ~1°. Because Jupiter's gaseous body does not rotate uniformly at all latitudes, astronomers have defined three different systems for defining 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 (). Despite this, however, the spot has "lapped" the planet in System II at least 10 times since the early 19th 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 A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interpl ...
storm () 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 "Sola ...
, little is known about its internal depth and structure. Visible imaging and cloud-tracking from
in-situ is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...
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'' mission, gravity signature and thermal infrared data were 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 layer. These MWR scans suggested that the GRS vertical depth extended to about below cloud level, with an estimated drop in atmospheric pressure to . Two methods of analysis that constrain the data collected were the mascon approach, which found a depth of , and the Slepian approach showing wind extending to . These methods, along with gravity signature MWR data, suggest that the GRS zonal winds still increase at a rate of 50% of 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 .
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...
and Cassini's thermal infrared imaging and
spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...
of the GRS were conducted during 1995–2008, in order to find evidence of thermal inhomogeneities within the internal structure vortex of the GRS. Previous thermal infrared temperature maps from the Voyager, Galileo, and Cassini missions suggested the GRS is a structure of an anticyclonic vortex with a cold core within a upwelling warmer annulus; this data shows a gradient in the temperature of the GRS. Better understanding of Jupiter's atmospheric temperature, aerosol particle opacity, and ammonia gas composition was provided by thermal-IR imaging: a direct correlation of the visible cloud layers reactions, thermal gradient and compositional mapping to observational data were collected over decades. During December 2000, high spatial resolution images from Galileo, of an atmospheric turbulent area to the northwest of the GRS, showed a thermal contrast between the warmest region of the anticyclone and regions to the east and west of the GRS. The vertical temperature of the structure of the GRS is constrained to be between 100 and , with the vertical temperature of the GRS core at approximately of pressure being , much warmer than regions of the GRS to the east–west, and warmer than regions to the north–south of the structure's edge. This structure is consistent with the data collected by the VISIR (VLT Mid-Infrared Imager Spectrometer on the ESO Very Large Telescope) imaging obtained in 2006; this revealed that the GRS was physically present at a wide range of altitudes that occur within the atmospheric pressure range of , and confirms the thermal infrared mapping result. To develop a model of the internal structure of the GRS, the Cassini instrument 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 functio ...
(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 chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
aerosols (, ) and para-hydroxybenzoic acid within the anticyclonic circulation of the GRS. The images that were collected from the CIRS and ground-based imaging trace the vertical motion in the Jovian atmosphere by and spectra. The highest concentrations of and were found to the north of the GRS peripheral rotation. They aided in determining the southward jet movement and showed evidence of an increase in altitude of the column of aerosols with pressures ranging from . However, the composition data shows that there is a major depletion of 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 mov ...
and compositional asymmetries of the GRS suggest that the structure exhibits a degree of tilt from the northern edge to the southern edge of the structure. The GRS depth and internal structure has been constantly changing over decades; however there is still no logical reason that it is 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 by 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 (Chemical nomenclature, systematic name: ethyne) is a 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 u ...
, 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 rays, cosmic ray irradiation of simple carbon-containing compounds su ...
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: between 1947 and 1997, the spot was darkest in the periods 1961–1966, 1968–1975, 1989–1990, and 1992–1993.


See also

* Extraterrestrial vortex *
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' ...
* Great White Spot, 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 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...
* Hypercane * WISEP J190648.47+401106.8


References


Further reading

* * * * * *


External links

* * * * *
Video based on Juno's Perijove 7 overflight
by Seán Doran (se
album
for more) {{Jupiter 1664 in science 1831 in science Jupiter Planetary spots Anticyclones Vortices Storms Robert Hooke