Great Red Spot

The Great Red Spot is a persistent, high-pressure region in the atmosphere of the planet Jupiter, producing the largest anticyclonic storm in the Solar System. 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's equator, 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. 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, who described a spot on the planet in May 1664. In the following year, Giovanni Cassini describes "a permanent [spot] which was often seen to return in the same place with the same size and shape", calculating its rotation period to be . Part of a series of panels in which different (magnified) heavenly bodies serve as backdrops for various Italian 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. 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, predicted the storms would have their closest passing on 4 July 2006. She worked with Imke de Pater and Phil Marcus of UC Berkeley as well as a team of professional astronomers beginning in April 2006 to study the storms using the Hubble Space Telescope; on 20 July 2006, the two storms were photographed passing each other by the Gemini Observatory 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. There is also a feature in the atmosphere of Neptune called the Great Dark Spot. The latter feature was imaged by Voyager 2 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

thumb|upright=1.25|Time-lapse sequence representing 28 days from the approach of Voyager 1 to Jupiter in early 1979, showing the motion of atmospheric bands and the circulation of the Great Red Spot. The momentary black spots are shadows cast by [[Moons of Jupiter|Jupiter's moons.]]

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. It has been shrinking for about a century, making it now slightly smaller than 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) to cause friction; circulating atmospheric eddies persist because there is nothing to oppose their angular momentum.

Infrared 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.

left|thumb|upright=1.2|Size of the Earth compared to the Great Red Spot

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 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 has been stable for the duration of good observational records, typically varying by about a degree. Its longitude, 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

thumb|400x400px|Clockwise from top left: [[Hubble Space Telescope|Hubble image of visible spectrum; infrared from the Gemini Observatory; multiwavelength composite of Hubble and Gemini data showing visible light in blue and thermal infrared in red; ultraviolet image from Hubble; visible light detail ]]

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 storm () in the 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 mission, gravity signature and thermal infrared data were obtained that offered insight into the structural dynamics and depth of the GRS.

left|thumb|400x400px|Winds in the Great Red Spot as analyzed from Hubble's data. In the false-color image at right, red indicates faster wind, blue indicates slower.

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. To develop a model of the internal structure of the GRS, the Cassini instrument Composite Infrared Spectrometer (CIRS) and ground based spatial imaging mapped the composition of the phosphine and ammonia 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. 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 GRS depth and internal structure has been constantly changing over decades; and the organic compound acetylene, which produces a reddish material—likely complex organic compounds called tholins. 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.

References

External links

Video based on Juno's Perijove 7 overflight by Seán Doran (see album for more)

Great Red Spot

Mechanical dynamics

Internal depth and structure

See also

References

Further reading

External links