Atmospheric super-rotation is a phenomenon where a planet's atmosphere rotates faster than the planet itself. This behavior is observed in the atmosphere of Venus, atmosphere of Titan, atmosphere of Jupiter, and atmosphere of Saturn. Venus exhibits the most extreme super-rotation, with its atmosphere circling the planet in four Earth days, much faster than its planet's own rotation. The phenomenon of atmospheric super-rotation can influence a planet's climate and atmospheric dynamics.
In understanding super-rotation, the role of atmospheric waves and instabilities is crucial. These dynamics, including Rossby waves and Kelvin waves, are integral in transferring momentum and energy within atmospheres, contributing to the maintenance of super-rotation. For instance, on Venus, the interaction of thermal tides with planetary-scale Rossby waves is thought to contribute significantly to its rapid super-rotational winds. Similarly, in Earth's atmosphere, Kelvin waves generate eastward along the equator, playing a vital role in phenomena like the El Niño-Southern Oscillation, demonstrating the broader implications of these dynamics in atmospheric science.
The atmosphere of Venus is a prominent case of extreme super-rotation; the Venusian atmosphere circles the planet in just four Earth days, much faster than Venus' sidereal day of 243 Earth days. [1] The initial observations of Venus' super rotation were Earth-based. Modern GCM models and observations are often enhanced by looking at past ancient climates. In a model where Venus is assumed to have an atmospheric mass similar to Earth, SS-AS circulation could have dominated over superrotation in an ancient thinner atmosphere. [2]
Superrotation present in the stratosphere of Titan has been inferred by Voyager IRIS, Cassini CIRIS, stellar occultation and temperature observations, and Doppler shifts of the Huygens probe’s radio signal. [3] Latitudinal pressure gradients established from measurements taken by Voyager IRIS were sufficient to produce superrotation of the atmosphere. [4] Stratospheric zonal winds on Titan were observed on the order of 100-200 m s−1, [5] faster than the highest zonal winds on Earth at ~60-70 m s−1. Questions on the effect of obliquity in superrotation on Titan is often compared to Venus, as they share similar centrifugal accelerations to achieve dynamic balance. Any seasonal variations effected by obliquity between Titan and Venus is much different, as the small obliquity of Venus at 2.7° negates any strong seasonal effects. Titans obliquity at 26.7° is high enough to cause seasonal variations within the stratospheric spin. [4] Attempts to model superrotation on the gas giants, including Titan, has been abundant. The first observations of Titan in the 1980's revealed little information about circulation within the atmosphere due to the low contrast photochemical haze covering the moon. The first general circulation model (GCMs) in the 1990s provided insight into the stratospheric properties that should be expected on Titan with further observation, and predicted superrotation with winds up to 200 m/s. [6] Superrotation was supported by the first 3D Titan GCM created by the Laboratoire de Météorologie Dynamique (LMD), in which they used an atmosphere similar to the observations of Voyager and recently Cassini.
The most recent GCM that is able to simulate superrotation in the stratosphere successfully is TitanWRF. Modeled after the PlanetWRF, which was designed to be a global weather, research, and forecasting (WRF) model, TitanWRF added planetary physics and generalized parameters to produce a successful superrotation model. Work done with TitanWRF v2 was able to simulate gradients in latitudinal temperature, zonal wind jets and superrotation in the stratosphere. [3] Comparing TitanWRF v2 simulations with constant solar forcing (seasonal cycle removed) models [7] , showed that in the latter, a rapid buildup in rotation, attaining > 100m/s, happened in a few Titan years. The parameters in these older forcing models differ greatly in the mechanisms involved in generating the initial superrotation compared to the more realistic TitanWRF models. After initial spin up, similarities evolve between the different models when a steady state is produced [3] , but differ again in the final states of the model. The initial mechanism producing spin up to superrotation is still an on going question, as correlations between models differ greatly within this regime.
The visible cloud tops of Jupiter and Saturn provides further evidence on its deep atmospheric circulation demonstrating the presence of atmospheric super-rotation. [8] Jupiter's auroras, in particular, highlight the planet's rapid atmospheric movements through their ethereal glow and varying cloud depths.
On Earth, there is a phenomenon that its thermosphere has a slight net super-rotation, exceeding the surface rotational velocity. The size of this phenomenon varies widely across different models. [9] [10] [11] Some models suggest that global warming is likely to cause an increase in super-rotation in the future, including possible change in surface winds patterns. [12] [13] In simplified GCM models, equatorial superrotation emerges without obliquity and the addition of tropical heating anomalies. [5] At present, a counter balance between the easterly Coriolis torque and the westerly torque maintains subrotation in the upper tropical troposphere. This leads to the prospect that with warmer and tropical wave sources in past ancient climates, Earths atmosphere might have superrotated. [14]
Super-rotation in planetary atmospheres extends to the study of exoplanets, particularly, hot Jupiters. These distant worlds, orbiting close to their stars, often exhibit extreme atmospheric conditions, including super-rotation, which influences their thermal structures and potential habitability. Observations from telescopes like the Hubble Space Telescope have unveiled super-rotational wind speeds of thousands of kilometers per hour on some hot Jupiters. Moreover, the phenomenon shows how hot Jupiters is tidally locked, where one side continuously faces the star. This suggests a mechanism for heat distribution in planets, a factor in understanding their climatic conditions and patterns.
Venus is the second planet from the Sun. It is a terrestrial planet and is the closest in mass and size to its orbital neighbour Earth. Venus is notable for having the densest atmosphere of the terrestrial planets, composed mostly of carbon dioxide with a thick, global sulfuric acid cloud cover. At the surface it has a mean temperature of 737 K and a pressure of 92 times that of Earth's at sea level. These conditions are extreme enough to compress carbon dioxide into a supercritical state close to Venus's surface.
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.
Atmospheric escape is the loss of planetary atmospheric gases to outer space. A number of different mechanisms can be responsible for atmospheric escape; these processes can be divided into thermal escape, non-thermal escape, and impact erosion. The relative importance of each loss process depends on the planet's escape velocity, its atmosphere composition, and its distance from its star. Escape occurs when molecular kinetic energy overcomes gravitational energy; in other words, a molecule can escape when it is moving faster than the escape velocity of its planet. Categorizing the rate of atmospheric escape in exoplanets is necessary to determining whether an atmosphere persists, and so the exoplanet's habitability and likelihood of life.
The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.85%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and noble gases. The atmosphere of Mars is much thinner and colder than Earth's having a max density 20g/m3 with a temperature generally below zero down to -60 Celsius. The average surface pressure is about 610 pascals (0.088 psi) which is less than 1% of the Earth's value.
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.
The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. Titan is the only natural satellite in the Solar System with an atmosphere that is denser than the atmosphere of Earth and is one of two moons with an atmosphere significant enough to drive weather. Titan's lower atmosphere is primarily composed of nitrogen (94.2%), methane (5.65%), and hydrogen (0.099%). There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene, propane, PAHs and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, acetonitrile, argon and helium. The isotopic study of nitrogen isotopes ratio also suggests acetonitrile may be present in quantities exceeding hydrogen cyanide and cyanoacetylene. The surface pressure is about 50% higher than on Earth at 1.5 bars which is near the triple point of methane and allows there to be gaseous methane in the atmosphere and liquid methane on the surface. The orange color as seen from space is produced by other more complex chemicals in small quantities, possibly tholins, tar-like organic precipitates.
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.
Polar wander is the motion of a pole in relation to some reference frame. It can be used, for example, to measure the degree to which Earth's magnetic poles have been observed to move relative to the Earth's rotation axis. It is also possible to use continents as reference and observe the relative motion of the magnetic pole relative to the different continents; by doing so, the relative motion of those two continents to each other can be observed over geologic time as paleomagnetism.
In atmospheric science, hydrodynamic escape refers to a thermal atmospheric escape mechanism that can lead to the escape of heavier atoms of a planetary atmosphere through numerous collisions with lighter atoms.
The NASA International Planetary Patrol Program consists of a network of astronomical observatories to collect uninterrupted images and observations of the large-scale atmospheric and surface features of the planets. This group was established in 1969, and consisted of the Mauna Kea Observatory, the Mount Stromlo Observatory, the Perth Observatory, the Republic Observatory, the Cerro Tololo Inter-American Observatory, the Magdalena Peak Station of the New Mexico State University, and the Lowell Observatory. The activities were coordinated by William A. Baum of Lowell Observatory. In the years from 1975 to 1981 the San Vittore Observatory (Bologna) Italy also participated with observations of Mars, Jupiter and Saturn.
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.
The length of the day (LOD), which has increased over the long term of Earth's history due to tidal effects, is also subject to fluctuations on a shorter scale of time. Exact measurements of time by atomic clocks and satellite laser ranging have revealed that the LOD is subject to a number of different changes. These subtle variations have periods that range from a few weeks to a few years. They are attributed to interactions between the dynamic atmosphere and Earth itself. The International Earth Rotation and Reference Systems Service monitors the changes.
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.
Donald B. Campbell is an Australian-born astronomer and Professor of Astronomy at Cornell University. Prior to joining the Cornell faculty he was Director of the Arecibo Observatory in Puerto Rico for seven years. Campbell's research work is in the general area of planetary studies with a concentration on the radio-wavelength-scattering properties of planets, planetary satellites, and small bodies. His work includes studies of Venus, the Moon, the Galilean satellites of Jupiter, Titan, as well as comets and asteroids. Campbell observed near-Earth asteroid 433 Eros, which was the first asteroid detected by the Arecibo Observatory radar system.
Planetary oceanography, also called astro-oceanography or exo-oceanography, is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry, and planetary geology, it only began after the discovery of underground oceans in Saturn's moon Titan and Jupiter's moon Europa. This field remains speculative until further missions reach the oceans beneath the rock or ice layer of the moons. There are many theories about oceans or even ocean worlds of celestial bodies in the Solar System, from oceans made of diamond in Neptune to a gigantic ocean of liquid hydrogen that may exist underneath Jupiter's surface.
Chemical cycling describes systems of repeated circulation of chemicals between other compounds, states and materials, and back to their original state, that occurs in space, and on many objects in space including the Earth. Active chemical cycling is known to occur in stars, many planets and natural satellites.
The dwarf planet Pluto has an unusual set of climate zones, due to its atypical axial configuration. Five climate zones are assigned on the dwarf planet: tropics, arctic, tropical arctic, diurnal, and polar. These climate zones are delineated based on astronomically defined boundaries or sub-solar latitudes, which are not associated with the atmospheric circulations on the dwarf planet. Charon, the largest moon of Pluto, is tidally locked with it, and thus has the same climate zone structure as Pluto itself.
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 with Jupiter.