Editing Ring system (section)

== Ring systems of planets ==
[[File:Saturn in natural colors (captured by the Hubble Space Telescope).jpg|thumb|upright=1.5|The ring orbiting [[Saturn]] consists mostly of chunks of ice and dust. The small dark spot on Saturn is the shadow from Saturn's moon [[Enceladus]].]]

The composition of planetary ring particles varies, ranging from silicates to icy dust. Larger rocks and boulders may also be present, as seen in 2007 when [[Tide|tidal]] effects from eight moonlets only a few hundred meters across were detected within Saturn's rings. The maximum size of a ring particle is determined by the [[specific strength]] of the material it is made of, its density, and the tidal force at its altitude. The tidal force is proportional to the average density inside the radius of the ring, or to the mass of the planet divided by the radius of the ring cubed. It is also inversely proportional to the square of the orbital period of the ring.

{{anchor|shepherds}}Some planetary rings are influenced by [[Shepherd moon|''shepherd moons'']], small [[Natural satellite|moons]] that orbit near the inner or outer edges of a ringlet or within gaps in the rings. The [[gravity]] of shepherd moons serves to maintain a sharply defined edge to the ring; material that drifts closer to the shepherd moon's orbit is either deflected back into the body of the ring, ejected from the system, or accreted onto the moon itself.

It is also predicted that [[Phobos (moon)|Phobos]], a moon of Mars, will break up and form into a planetary ring in about 50 million years. Its low orbit, with an orbital period that is shorter than a Martian day, is decaying due to [[tidal deceleration]].<ref name="Holsapple2001"/><ref>Gürtler, J. & Dorschner, J: "''Das Sonnensystem''", Barth (1993), {{ISBN|3-335-00281-4}}</ref>

=== Jupiter ===
{{main|Rings of Jupiter}}
Jupiter's ring system was the third to be discovered, when it was first observed by the ''[[Voyager 1]]'' probe in 1979,<ref name="smith1979"/> and was observed more thoroughly by the ''Galileo'' orbiter in the 1990s.<ref name="ockert-bell1999"/> Its four main parts are a faint thick torus known as the "halo"; a thin, relatively bright main ring; and two wide, faint "gossamer rings".<ref name="esposito2002"/> The system consists mostly of dust.<ref name="smith1979"/><ref name="showalter1987"/>

===Saturn===
{{main|Rings of Saturn}}
Saturn's rings are the most extensive ring system of any planet in the Solar System, and thus have been known to exist for quite some time. [[Galileo Galilei]] first observed them in 1610, but they were not accurately described as a disk around Saturn until [[Christiaan Huygens]] did so in 1655.<ref name="solarviews"/> The rings are not a series of tiny ringlets as many think, but are more of a disk with varying density.<ref name="tiscareno2013"/> They consist mostly of water ice and trace amounts of [[Rock (geology)|rock]], and the particles range in size from micrometers to meters.<ref name="ciclops"/>

===Uranus===
{{main|Rings of Uranus}}
Uranus's ring system lies between the level of complexity of Saturn's vast system and the simpler systems around Jupiter and Neptune. They were discovered in 1977 by [[James L. Elliot]], Edward W. Dunham, and [[Jessica Mink]].<ref name="elliot1977"/> In the time between then and 2005, observations by ''[[Voyager 2]]''<ref name="smith1986"/> and the [[Hubble Space Telescope]]<ref name="showalter2006"/> led to a total of 13 distinct rings being identified, most of which are opaque and only a few kilometers wide. They are dark and likely consist of water ice and some radiation-processed [[Organic compound|organics]]. The relative lack of dust is due to [[aerodynamic drag]] from the extended [[exosphere]]-[[Uranus|corona]] of Uranus.

===Neptune===
{{main|Rings of Neptune}}
The system around Neptune consists of five principal rings that, at their densest, are comparable to the low-density regions of Saturn's rings. However, they are faint and dusty, much more similar in structure to those of Jupiter. The very dark material that makes up the rings is likely organics processed by [[radiation]], like in the rings of Uranus.<ref name="smith1989"/> 20 to 70 percent of the rings are [[Cosmic dust|dust]], a relatively high proportion.<ref name="smith1989"/> Hints of the rings were seen [[Rings of Neptune|for decades]] prior to their conclusive discovery by ''Voyager 2'' in 1989.

=== Prehistoric ring systems ===

==== Earth ====
{{main|Rings of Earth}}

A 2024 study suggests that Earth may have had a ring system for a period of 40 million years, starting from the middle of the [[Ordovician]] period (around 466 million years ago). This ring system may have originated from a large asteroid that passed by Earth at this time and had a significant amount of debris stripped by Earth's gravitational pull, forming a ring system. Evidence for this ring comes from impact craters from the [[Ordovician meteor event]] appearing to cluster in a distinctive band around the Earth's equator at that time. The presence of this ring may have led to significant shielding of Earth from sun's rays and a severe cooling event, thus causing the [[Andean-Saharan glaciation|Hirnantian glaciation]], the coldest known period of the last 450 million years.<ref name=":0">{{Cite journal |last1=Tomkins |first1=Andrew G. |last2=Martin |first2=Erin L. |last3=Cawood |first3=Peter A. |date=2024-11-15 |title=Evidence suggesting that earth had a ring in the Ordovician |journal=Earth and Planetary Science Letters |volume=646 |pages=118991 |doi=10.1016/j.epsl.2024.118991 |issn=0012-821X|doi-access=free |bibcode=2024E&PSL.64618991T }}</ref>