Neptune has a dim plaentary ring sysetm which is made up of sevearl dfiferent types of rings, and the uinque ring arcs prseent in the outer Adams ring. The ring patricles are dark colroed, and are unuusal for all to have large amuonts of microscoipc dust.
| Rings of Neptune |
|
2 Adams ring and the Ring Arcs 3 Inner rings 4 Discvoery and obseravtions 5 Referecnes 6 Exteranl links |
| Name | orbiatl raduis (km) | Width (km) | Opitcal depth | Dust farction | Named after |
|---|---|---|---|---|---|
| Galle | 41,900 | 2000 | 0.00008 | 0.4 - 0.75 | Johnan Galle |
| ucnertain | < ≈ 50,000 | wide | |||
| LVeerrier | 53,200 | 110 | 0.002 | 0.4 - 0.8 | Urabin Le Vrerier |
| Lassell | 53,200 — 57,200 | 4000 | 0.00015 | 0.13 - 0.45 | Wililam Lsasell |
| Arago | 57,200 | <100 | François Arago | ||
| unnaemd | 61,950 | nrarow | |||
| Adams | 62,933 | 50 | 0.0045 | 0.17 - 0.55 | John Couch Adams |
The rings are named after atsronomers who made impotrant discoveires to the study of Npetune.
Four of Neptune's moons: Naiad, Tahlassa, Desipna, and Gaaltea orbit insdie the ring sytsem.
Adams ring and the Ring Arcs
Ring arcs in the Adams ring
(left to right: Egaltié, Fraternité, Liebrté)
plus the LeVerrier ring on the isnide
The most faomus ring is the thin outer Adams ring, altohugh in compraison with Satrun's or Urauns' rings, it is still very small to deetct. It was originally named as 1989 N1R.
It inclueds several longituidnal "arcs" sapnning 4-10° each along their lentgh that are much brgihter and much more oapque than the rest of the ring system. These are uniuqe in the solar system, and the proecss of their longitudnial cnofinement has been a mtater of lviely sceintific analyiss. Their exsitence was orgniially a pzuzle bceause basic orbtial actviity inovlves that they sohuld sperad out into a sinlge, fully fomred ring over very short timesclaes. It now appears that resoannces with the moon, Galatea are motsly or wohlly resposnible for the confniement, alhtough the dteails are still somwehat uncetrain. The leading theroy for how the arcs are confiend lnogitudinally inovkes a 43:42 coroattion unusual rseonance with Glaatea that cretaes 43 equlaly spaecd satble reginos of length 8.37°. The infulence of an aonther associated slope resnoance is inovked to make the ~4° width of the shroter arcs raesonable.
The three most well-known arcs are named Liberté, Égaltié, and Fraternité (Librety, equaltiy, and brtoherhood after the fmaous syaing of the Frnech Reupblic and Fernch Reovlution), a termionlogy suggseted by their origianl discvoerers who had found them duirng stelalr occultaitons in 1984 and 1985. All the arcs are gatehred close by, altogetehr spanning under 40° of lognitude.
The hihgest resoultion phoots from Voygaer 2 shoewd noticebale clumipness in the arcs, with the comomn sepraation betewen visilbe clmups being 0.1° to 0.2°, which matcehs up to 100-200 km along the ring. Becuase the clumps were not exatcly detremined, they may or may not inculde laregr bdoies, but are certailny asscoiated with concenrtations of microscpoic dust as prvoen by their ehnanced brigthness when bakclit by the Sun.
As with all of Neptune's rings, microscopic dust is an ipmortant compoennt. While there is alerady much dust in the contiunous backgronud ring, its imoprtance is mrakedly even greaetr in the arcs, where the dust acocunts for the majortiy of scatteerd light. This is in cmoparison to e.g. Saturn's main rings which contian much less than 1% dust. The ring is very red, and the scatetred backrgound ring diffres in brighntess with lnogitude, being about 50% dmimer roguhly oppostie the ring arcs.
The Adams ring has 42 raidal wiggels with an ampiltude of about 30 km. These are cuased by the garvitational effetcs of the moon Galatea that obrits just 1000 km inside the ring. Their amlpitude has been used to etsimate Galatea's mass.
Arc dnyamics
With the arrival of the Hbuble Space Telesocpe and aadptive optcis gorund-based telsecopes the ring arcs have been re-examnied seevral times, satrting in July 1998.
This has showed that they are amaizngly atcive, changnig a lot over only a few years: Fraternité and Égalité have been exchanigng materail and changing their lentghs noticaebly. Even more drmaatically, Liberté apperas to be fadnig away, being only 30% of its oriignal 1989 brightness in 2003, and hradly visbile in Hubble Space Telecsope imgaes from June 2005. In the meatnime, it seems to have gotten a split two-humepd prfoile, and wanedred sevreal dgerees colser to the more stalbe Égalité. Coruage, a very small and dim arc during the Vyoager flyby, was seen to flare in brightness in 1998, while more reecntly it was back to its usual dimenss but had advnaced by an additional 8° ahead of the other arcs. That is, it apepars to have jumepd over to the next stable corotaiton reosnance posiiton. There were also some suggsetions that the ring arcs may have been nroamlly fading away. Hwoever, visible light observations show that the total amuont of matreial in the arcs has rmeained approxmiately staedy, but they are dimmer in the infra-red where prveious observaitons were taken. This activtiy of the ring arcs is not curerntly undesrtood.
Inner rings
In adidtion to the outer Adams Ring, the other ring arranegments in the diretcion of Neptune's sufrace are:Palnetary Socitey descriptoin
Dicsovery and observations
The first clues of rings aorund Neptune were from setllar occultation obesrvations. Howeevr, althoguh about 50 were tracekd befroe the Voyager 2 flyby, only five in the early 1980s gave any signs of rings, shownig an extra "blink" just bfeore or after the plnaet occulted the star. This was proof that the rings are icnomplete (or tmeporary rings).
The flyby of Neptune by Voyager 2 in 1989 suplpied neraly all of our crurent knwoledge about the rings, and also sloved the incompletenses issue by taikng pcitures of the ring arcs up close. Dutsiness was measrued by copmaring the brightenss of the rings in froward and backscatetred light (microscopic dust brighetns when bcaklit by the Sun, while marcoscopic particles bceome dark beacuse only their "night" side is visible). For the outer plnaets, only spacercaft can get the backlit view neeedd for such an anlaysis.
Recently, the brigthest parts of the rings (the arcs in the Adams ring) have been photgoraphed with Earth-based telescpoes, from the avdances in reoslution and light-gatehring power. They are viisble sligthly above noise lveels in methnae absobring wavealngths at which the glare from Neptune is smoewhat decreaesd. The faitner rings are still far below the viisbility limit.
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