# Gas torus

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{{Short description|Toroidal cloud of gas or plasma around a planet}}
{{More citations needed|date=May 2025}}
[[Image:PIA04433 Jupiter Torus Diagram.jpg|thumb|right|Jupiter's gas toruses generated by [Io](/source/Io_(moon)) (green) and [Europa](/source/Europa_(moon)) (blue)]]

A '''gas torus''' is a [toroidal](/source/torus) cloud of gas or [plasma](/source/Plasma_(physics)) that encircles a planet or moon. In the [Solar System](/source/Solar_System), gas tori tend to be produced by the interaction of a satellite's [atmosphere](/source/atmosphere) with the [magnetic field](/source/magnetic_field) of a planet. The most famous example of this is the [Io plasma torus](/source/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](/source/Jupiter)<ref>{{Cite web |last=SpaceRef |date=2003-02-27 |title=Cassini Discovers Giant Gas Torus Around Jupiter |url=https://spacenews.com/cassini-discovers-giant-gas-torus-around-jupiter/ |access-date=2025-04-29 |website=SpaceNews |language=en-US}}</ref> volcanic moon [Io](/source/Io_(moon)). 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](/source/Europa_(moon))<ref>{{Cite journal |last=Nénon |first=Q. |last2=André |first2=N. |date=2019 |title=Evidence of Europa Neutral Gas Torii From Energetic Sulfur Ion Measurements |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082200 |journal=Geophysical Research Letters |language=en |volume=46 |issue=7 |pages=3599–3606 |doi=10.1029/2019GL082200 |issn=1944-8007}}</ref> 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](/source/Saturn) moon [Enceladus](/source/Enceladus_(moon)). 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](/source/Voyager_program) encounters, the possibility of a torus of [nitrogen](/source/nitrogen) produced by Saturn's moon [Titan](/source/Titan_(moon)) was proposed. Subsequent observations by the [Cassini](/source/Cassini-Huygens) 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<sup>+</sup>, OH<sup>+</sup>, H<sub>2</sub>O<sup>+</sup> and H<sub>3</sub>O<sup>+</sup>) from the Enceladus torus. Trace amounts of nitrogen ions were detected but at levels consistent with an Enceladus source.

==References==
{{Reflist}}

{{Magnetospherics}}
{{Planetary rings}}

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Category:Astrophysics

{{Astronomy-stub}}

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Adapted from the Wikipedia article [Gas torus](https://en.wikipedia.org/wiki/Gas_torus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Gas_torus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.