A gas torus is a toroidal cloud of gas or plasma that encircles a planet or moon. 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 ...

, gas tori tend to be produced by the interaction of a satellite's

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

with the

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

of a planet. The most famous example of this is the Io plasma torus, which is produced by the ionization of roughly 1 ton per second of oxygen and sulfur from the tenuous atmosphere of Jupiter's volcanic moon Io. Before being ionized, these particles are part of a neutral torus, also centered on the orbit of Io. Energetic particle observations also suggest the presence of a neutral torus around the orbit of Jupiter's moon

Europa Europa may refer to: Places * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Cliffs, Alexan ...

although such a torus would be merged with the outer portions of an Io torus. Other examples include the largely neutral torus of oxygen and hydrogen produced by

Saturn's 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 times ...

moon

Enceladus Enceladus is the sixth-largest moon of Saturn and the 18th-largest in the Solar System. It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. It is covered by clean, freshly deposited snow hundreds of meters thick, ...

. The Enceladus and Io tori differ in that particles in the Io torus are predominantly ionized while in the Enceladus torus, the neutral density is much greater than the ion density. After the

Voyager Voyager may refer to: Computing and communications * LG Voyager, a mobile phone model manufactured by LG Electronics * NCR Voyager, a computer platform produced by NCR Corporation * Voyager (computer worm), a computer worm affecting Oracle ...

encounters, the possibility of a torus of

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

produced by Saturn's moon

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

was proposed. Subsequent observations by the Cassini spacecraft showed no clear evidence of such a torus. While neutral nitrogen could not be measured, the ions near the orbit of Titan were primarily hydrogen or water group (O⁺, OH⁺, H₂O⁺ and H₃O⁺) from the Enceladus torus. Trace amounts of nitrogen ions were detected but at levels consistent with an Enceladus source.

References

Astrophysics {{Astronomy-stub