Great Dark Spot

Last updated April 13, 2024

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 Voyager 2 space probe. Like Jupiter's spot, Great Dark Spots are anticyclonic storms. However, their interiors are relatively cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be shorter, forming and dissipating once every few years or so. Based on observations taken with Voyager 2 and since then with the Hubble Space Telescope, Neptune appears to spend somewhat more than half its time with a Great Dark Spot. Little is known about the origins, movement, and disappearance of the dark spots observed on the planet since 1989.

Characteristics

The Great Dark Spot was captured by NASA's Voyager 2 space probe in Neptune's southern hemisphere. The dark, elliptically shaped spot (with initial dimensions of 13,000 × 6,600 km, or 8,100 × 4,100 mi of GDS-89 was about the same size as Earth, and was similar in general appearance to Jupiter's Great Red Spot. One major difference compared to Jupiter's Great Red Spot is that Neptune's Great Dark Spot has shown the ability to shift north-south over time, while the Great Red Spot is held in the same latitudinal region by global east-west wind currents.^[1] Around the edges of the storm, winds were measured at up to 2,100 kilometers per hour (1,300 mph), the fastest recorded in the Solar System. The Great Dark Spot is thought to be a hole in the methane cloud deck of Neptune. The spot was observed at different times with different sizes and shapes.

The Great Dark Spot generated large white clouds at or just below the tropopause layer similar to high-altitude cirrus clouds found on Earth. Unlike the clouds on Earth, however, which are composed of crystals of water ice, Neptune's cirrus clouds are made up of crystals of frozen methane. These high altitude clouds are located somewhere between 50–100 km (30–60 miles) above the main cloud deck.^[2] While cirrus clouds usually form and then disperse within a period of a few hours, the clouds in the Great Dark Spot were still present after 36 hours, or two rotations of the planet.

Neptune's dark spots are thought to occur in the troposphere at lower altitudes than the brighter upper cloud deck features. As they are stable features that can persist for several months, they are thought to be vortex structures.

Disappearance

When the spot was to be photographed again in November 1994 by the Hubble Space Telescope, it had disappeared completely, leaving astronomers to believe that it had either been covered up or had vanished. The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature. Dark spots may dissipate when they migrate too close to the equator, or possibly through some other unknown mechanisms.^[4]

Other dark spots observed

Following the Great Dark Spot, several other dark spots have been observed. In 1989, when the Voyager 2 observed the Great Dark Spot (GDS), a second dark spot, Dark Spot 2 (DS2) was found. Dark Spot 2 fully dissipated prior to the year 1994. ^[6] Beginning in 1994, the Hubble became the only operating facility to detect the presence and observe dark spots on Neptune and is still used to the present day.^[7] Hubble is able to view images at blue wavelength, which is the only way features are visible. In 1994, a Northern Dark Spot (NGDS-1994) formed in the northern hemisphere and disappeared between 1998 and 2000. The storm for its duration showed to be stable in latitude.^[8]^[6] In 1996, a separate Northern Dark Spot (NGDS-1996) formed and was observed until its disappearance, which occurred prior to 1998. Similarly to the prior dark spot, this one exhibited little to no meridional drift.^[8]^[6] In 2015, a Southern Dark Spot (SDS) was discovered by the Hubble Outer Planet Atmosphere Legacy (OPAL) program.^[9] The Southern Dark Spot exhibited a poleward drift before its disappearance in 2017. In 2016, an almost identical spot as the Great Dark Spot (GDS) emerged in Neptune's northern hemisphere. This new spot, called the Northern Great Dark Spot (NGDS), has remained visible for several years. It is unknown whether this spot is still present on the planet, as observations using the Hubble telescope are limited.

More recently, in 2018, a newer main dark spot and a smaller dark spot were identified and studied. This discovery of the dark spot in Neptune's northern hemisphere was monumental in that it was the first dark spot that the Hubble Telescope was able to document from birth. The storm is much smaller in comparison than the one discovered by NASA's Voyager 2, but was found to be larger in diameter than the Atlantic Ocean at approximately 4,600 miles across.^[10] In August 2020, the new Great Dark Spot suddenly stopped its southward motion and reversed direction, contrary to projections that the storm would continue to the equator, where it would have met its likely demise. It is believed that the storms remain stable in the northern hemisphere due to the effect of Coriolis forces. However, as the storms moved towards the equator, the Coriolis forces weakened, causing the storms to dissipate.

Around the same time, a smaller "Dark Spot Jr." was found near the larger storm, before disappearing later on. Dark Spot Jr. as the name suggests was smaller than the prior dark spot, only measuring 3,900 miles in diameter. The coincidental appearance of this storm led astronomers to believe that the prior storm's reversal of motion may have been related to the birth of the smaller storm.

While the formation of the storms is still under investigation, it had been concluded from observations regarding the Southern Dark Spot (SDS-2015) and Northern Great Dark Spot (NGDS-2018) that their origins are preceded by an increase in cloud activity in the given region 2–3 years prior to becoming visible.^[9] The storms from 1989–2018 have exhibited different movement patterns and are generally only visible for a few years. Furthermore, the disappearance of dark spots including the Southern Dark Spot can be linked to companion clouds reaching the center of the storm and blocking the view of the blue wavelengths that are used to track the vortex, prior to their disappearance.^[6]

Proposed missions

Two mission ideas have been proposed to NASA to visit Neptune in the coming years. Trident was proposed in 2021 as a discovery mission to visit Neptune and its moon Triton in the year, but two missions to Venus (DAVINCI+ and VERITAS) were selected over it. Neptune Odyssey is a flagship orbiter mission concept with similar goals as Trident and is targeted for a launch date of 2033. These missions have a high focus on learning more about Neptune's largest moon Triton, but also aim to gain more information about the atmosphere of Neptune. An analysis of a nuclear-electric propulsion mission to Neptune was published by the China National Space Administration.^[11]

Related Research Articles

Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is currently carried out mainly by astronomers with telescopes, its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science.

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 trajectory that took longer to reach gas giants Jupiter and Saturn but enabled further encounters with ice giants Uranus and Neptune. Voyager 2 remains the only spacecraft to have visited either of the ice giant planets, and was the third of five spacecraft to achieve Solar escape velocity, which will allow it to leave the Solar System.

Jupiter is the fifth planet from the Sun and the 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, and slightly less than one one-thousandth the mass of the Sun. Jupiter orbits the Sun at a distance of 5.20 AU (778.5 Gm) with an orbital period of 11.86 years. Jupiter is the third brightest natural object in the Earth's night sky after the Moon and Venus, and it has been observed since prehistoric times. It was named after Jupiter, the chief deity of ancient Roman religion.

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, but is over 95 times more massive. Even though Saturn is nearly the size of Jupiter, Saturn has less than one-third of Jupiter's mass. Saturn orbits the Sun at a distance of 9.59 AU (1,434 million km) with an orbital period of 29.45 years.

Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a supercritical phase of matter, which in astronomy is called 'ice' or volatiles. The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature of 49 K out of all the Solar System's planets. It has a marked axial tilt of 82.23° with a retrograde rotation period of 17 hours and 14 minutes. This means that in an 84-Earth-year orbital period around the Sun, its poles get around 42 years of continuous sunlight, followed by 42 years of continuous darkness.

The Great Red Spot is a persistent high-pressure region in the atmosphere of Jupiter, producing an anticyclonic storm that is the largest 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 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 359 years. It was next observed in September 1831, with 60 recorded observations between then and 1878, when continuous observations began.

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. Unlike a cyclonic storm, anticyclonic storms are typically associated with fair weather and stable atmospheric conditions. On other planets or in rare cases on Earth, anticyclones can contribute to inclement weather. Examples include Hartmut, which brought a blizzard to the British Isles in 2018, Jupiter, and Neptune's persistent anticyclonic storms.

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 characteristic white appearance. The spots can be several thousands of kilometers wide.

The Small Dark Spot, sometimes also called Dark Spot 2 or The Wizard's Eye, was an extraterrestrial vortex on the planet Neptune. It was the second largest southern cyclonic storm on the planet in 1989, when Voyager 2 flew by the planet. When the Hubble Space Telescope observed Neptune in 1994, the storm had disappeared.

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 dust storms have been known to produce vortices on Mars and Titan. Various spacecraft missions have recorded evidence of past and present extraterrestrial vortices. The largest extraterrestrial vortices are found on the gas giants, Jupiter and Saturn, and the ice giants, Uranus and Neptune.

The study of extraterrestrial atmospheres is an active field of research, both as an aspect of astronomy and to gain insight into Earth's atmosphere. In addition to Earth, many of the other astronomical objects in the Solar System have atmospheres. These include all the gas giants, as well as Mars, Venus and Titan. Several moons and other bodies also have atmospheres, as do comets and the Sun. There is evidence that extrasolar planets can have an atmosphere. Comparisons of these atmospheres to one another and to Earth's atmosphere broaden our basic understanding of atmospheric processes such as the greenhouse effect, aerosol and cloud physics, and atmospheric chemistry and dynamics.

Neptune has been directly explored by one space probe, Voyager 2, in 1989. As of 2024, there are no confirmed future missions to visit the Neptunian system, although a tentative Chinese mission has been planned for launch in 2024. NASA, ESA, and independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.

The atmosphere of Uranus is composed primarily of hydrogen and helium. At depth it is significantly enriched in volatiles such as water, ammonia and methane. The opposite is true for the upper atmosphere, which contains very few gases heavier than hydrogen and helium due to its low temperature. Uranus's atmosphere is the coldest of all the planets, with its temperature reaching as low as 49 K.

Heidi B. Hammel is a planetary astronomer who has extensively studied Neptune and Uranus. She was part of the team imaging Neptune from Voyager 2 in 1989. She led the team using the Hubble Space Telescope to view Shoemaker-Levy 9's impact with Jupiter in 1994. She has used the Hubble Space Telescope and the Keck Telescope to study Uranus and Neptune, discovering new information about dark spots, planetary storms and Uranus' rings. In 2002, she was selected as an interdisciplinary scientist for the James Webb Space Telescope.

<span class="mw-page-title-main">Climate of Uranus</span>

The climate of Uranus is heavily influenced by both its lack of internal heat, which limits atmospheric activity, and by its extreme axial tilt, which induces intense seasonal variation. Uranus's atmosphere is remarkably bland in comparison to the other giant planets which it otherwise closely resembles. When Voyager 2 flew by Uranus in 1986, it observed a total of ten cloud features across the entire planet. Later observations from the ground or by the Hubble Space Telescope made in the 1990s and the 2000s revealed bright clouds in the northern (winter) hemisphere. In 2006 a dark spot similar to the Great Dark Spot on Neptune was detected.

Neptune is the eighth and farthest known planet from the Sun. 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 the mass of Earth, and slightly more massive than fellow ice giant Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. Being composed primarily of gases and liquids, it has no well-defined solid surface. The planet orbits the Sun once every 164.8 years at an orbital distance of 30.1 astronomical units. It is named after the Roman god of the sea and has the astronomical symbol , representing Neptune's trident.

The exploration of Io, Jupiter's innermost Galilean and third-largest moon, began with its discovery in 1610 and continues today with Earth-based observations and visits by spacecraft to the Jupiter system. Italian astronomer Galileo Galilei was the first to record an observation of Io on January 8, 1610, though Simon Marius may have also observed Io at around the same time. During the 17th century, observations of Io and the other Galilean satellites helped with the measurement of longitude by map makers and surveyors, with validation of Kepler's Third Law of planetary motion, and with measurement of the speed of light. Based on ephemerides produced by astronomer Giovanni Cassini and others, Pierre-Simon Laplace created a mathematical theory to explain the resonant orbits of three of Jupiter's moons, Io, Europa, and Ganymede. This resonance was later found to have a profound effect on the geologies of these moons. Improved telescope technology in the late 19th and 20th centuries allowed astronomers to resolve large-scale surface features on Io as well as to estimate its diameter and mass.

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, ammonia, hydrogen sulfide, and water. Although water is thought to reside deep in the atmosphere, its directly measured concentration is very low. The nitrogen, sulfur, and noble gas abundances in Jupiter's atmosphere exceed solar values by a factor of about three.

Saturn's hexagon is a persistent approximately hexagonal cloud pattern around the north pole of the planet Saturn, located at about 78°N. The sides of the hexagon are about 14,500 km (9,000 mi) long, which is about 2,000 km (1,200 mi) longer than the diameter of Earth. The hexagon may be a bit more than 29,000 km (18,000 mi) wide, may be 300 km (190 mi) high, and may be a jet stream made of atmospheric gases moving at 320 km/h (200 mph). It rotates with a period of 10h 39m 24s, the same period as Saturn's radio emissions from its interior. The hexagon does not shift in longitude like other clouds in the visible atmosphere.

Amy Simon is an American planetary scientist at NASA's Goddard Space Flight Center, involved in several missions of the Solar System Exploration Program.

References

↑ ""The Mystery Continues" --New Hubble Observations of Neptune's Great Dark Spot". The Daily Galaxy. 2021-08-29. Retrieved 2022-05-01.
↑ "Urbain-Jean-Joseph Le Verrier | Britannica". www.britannica.com. Retrieved 2022-05-01.
↑ "Dark spot on Neptune". ESA/Hubble . 27 June 2016. Retrieved 28 June 2016.
↑ Sromovsky, L. A.; Fry, P. M.; Dowling, T. E.; Baines, K. H. (2000). "The unusual dynamics of new dark spots on Neptune". Bulletin of the American Astronomical Society. 32: 1005. Bibcode:2000DPS....32.0903S.
↑ Lavoie, Sue (8 January 1998). "PIA01142: Neptune Scooter". NASA. Archived from the original on 29 October 2013. Retrieved 26 March 2006.
1 2 3 4 Wong, Michael H.; Tollefson, Joshua; Hsu, Andrew I.; Pater, Imke de; Simon, Amy A.; Hueso, Ricardo; Sánchez-Lavega, Agustín; Sromovsky, Lawrence; Fry, Patrick; Luszcz-Cook, Statia; Hammel, Heidi (2018-02-15). "A New Dark Vortex on Neptune". The Astronomical Journal. 155 (3): 117. Bibcode:2018AJ....155..117W. doi: 10.3847/1538-3881/aaa6d6 . ISSN 1538-3881. S2CID 125410572.
↑ Hsu, Andrew I.; Wong, Michael H.; Simon, Amy A. (2019-03-25). "Lifetimes and Occurrence Rates of Dark Vortices on Neptune from 25 Years of Hubble Space Telescope Images". The Astronomical Journal. 157 (4): 152. Bibcode:2019AJ....157..152H. doi: 10.3847/1538-3881/ab0747 . ISSN 1538-3881. S2CID 127269903.
1 2 Sromovsky, L. A.; Fry, P. M.; Baines, K. H. (2002-03-01). "The Unusual Dynamics of Northern Dark Spots on Neptune". Icarus. 156 (1): 16–36. Bibcode:2002Icar..156...16S. doi:10.1006/icar.2001.6761. ISSN 0019-1035.
1 2 Simon, A. A.; Wong, M. H.; Hsu, A. I. (2019-03-28). "Formation of a New Great Dark Spot on Neptune in 2018". Geophysical Research Letters. 46 (6): 3108–3113. Bibcode:2019GeoRL..46.3108S. doi:10.1029/2019GL081961. ISSN 0094-8276. S2CID 135445270.
↑ Jenner, Lynn (2020-12-14). "Dark Storm on Neptune Reverses Direction, Possibly Shedding a Fragment". NASA. Retrieved 2022-05-01.
↑ Yu, GuoBin; Wang, PengFei; Zhu, AnWen; Niu, JunPo; Xie, QiLin; Hu, Gu; Li, Hui; He, JianSen (1 June 2021). "Mission analysis of a Neptune detector with a 10 kWe nuclear reactor power generator". SCIENTIA SINICA Technologica. 51 (6): 711–721. doi:10.1360/SST-2020-0399.

External links

Neptune's Great Dark Spot of 1989, Windows to the Universe
Neptune's Great Dark Spot: Gone But Not Forgotten, Astronomy Picture of the Day , May 8, 1996

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[1] ""The Mystery Continues" --New Hubble Observations of Neptune's Great Dark Spot". The Daily Galaxy. 2021-08-29. Retrieved 2022-05-01.

[2] "Urbain-Jean-Joseph Le Verrier | Britannica". www.britannica.com. Retrieved 2022-05-01.

[3] "Dark spot on Neptune". ESA/Hubble . 27 June 2016. Retrieved 28 June 2016.

[Sromovsky_2000-4] Sromovsky, L. A.; Fry, P. M.; Dowling, T. E.; Baines, K. H. (2000). "The unusual dynamics of new dark spots on Neptune". Bulletin of the American Astronomical Society. 32: 1005. Bibcode:2000DPS....32.0903S.

[scooter-5] Lavoie, Sue (8 January 1998). "PIA01142: Neptune Scooter". NASA. Archived from the original on 29 October 2013. Retrieved 26 March 2006.

[:0-6] 1 2 3 4 Wong, Michael H.; Tollefson, Joshua; Hsu, Andrew I.; Pater, Imke de; Simon, Amy A.; Hueso, Ricardo; Sánchez-Lavega, Agustín; Sromovsky, Lawrence; Fry, Patrick; Luszcz-Cook, Statia; Hammel, Heidi (2018-02-15). "A New Dark Vortex on Neptune". The Astronomical Journal. 155 (3): 117. Bibcode:2018AJ....155..117W. doi: 10.3847/1538-3881/aaa6d6 . ISSN 1538-3881. S2CID 125410572.

[7] Hsu, Andrew I.; Wong, Michael H.; Simon, Amy A. (2019-03-25). "Lifetimes and Occurrence Rates of Dark Vortices on Neptune from 25 Years of Hubble Space Telescope Images". The Astronomical Journal. 157 (4): 152. Bibcode:2019AJ....157..152H. doi: 10.3847/1538-3881/ab0747 . ISSN 1538-3881. S2CID 127269903.

[:1-8] 1 2 Sromovsky, L. A.; Fry, P. M.; Baines, K. H. (2002-03-01). "The Unusual Dynamics of Northern Dark Spots on Neptune". Icarus. 156 (1): 16–36. Bibcode:2002Icar..156...16S. doi:10.1006/icar.2001.6761. ISSN 0019-1035.

[:2-9] 1 2 Simon, A. A.; Wong, M. H.; Hsu, A. I. (2019-03-28). "Formation of a New Great Dark Spot on Neptune in 2018". Geophysical Research Letters. 46 (6): 3108–3113. Bibcode:2019GeoRL..46.3108S. doi:10.1029/2019GL081961. ISSN 0094-8276. S2CID 135445270.

[10] Jenner, Lynn (2020-12-14). "Dark Storm on Neptune Reverses Direction, Possibly Shedding a Fragment". NASA. Retrieved 2022-05-01.

[11] Yu, GuoBin; Wang, PengFei; Zhu, AnWen; Niu, JunPo; Xie, QiLin; Hu, Gu; Li, Hui; He, JianSen (1 June 2021). "Mission analysis of a Neptune detector with a 10 kWe nuclear reactor power generator". SCIENTIA SINICA Technologica. 51 (6): 711–721. doi:10.1360/SST-2020-0399.

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