{"id":53868,"date":"2024-01-16T09:46:45","date_gmt":"2024-01-16T09:46:45","guid":{"rendered":"http:\/\/fb20120c-fe26-4032-9a76-b03f5b956e79"},"modified":"2024-01-16T10:32:34","modified_gmt":"2024-01-16T10:32:34","slug":"a-guide-to-rings-around-planets-and-across-the-solar-system","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/a-guide-to-rings-around-planets-and-across-the-solar-system\/","title":{"rendered":"A guide to rings around planets and across the Solar System"},"content":{"rendered":"

Our Solar System is full of rings, and not just around the planets. <\/p>

By Jane Green\n <\/p>

Published: Tuesday, 16 January 2024 at 09:46 AM<\/p>

\n\n

Whether comprised of silicates, icy dust, water ice or rock and whether micrometre, multi-metre or millions of kilometres in size, all the rings in our Solar System are detritus, relics of our star\u2019s protoplanetary disc.<\/p>

Rings litter a Solar System where \u2018roundness\u2019 rules.<\/p>

The spinning Sun, planets and moons are all near-spherical. Why are planets round<\/a>?<\/p>

Were rings instrumental in the evolution of our Solar System? Are rings relevant or mere rejects?<\/p>

Do discs denote rise or demise, or neither?<\/p>

A view of Uranus, its rings and moons captured by the NIRCam (Near-Infrared Camera) on the James Webb Space Telescope. Credit: NASA, ESA, CSA, STScI<\/figcaption><\/figure>

The Oort Cloud<\/strong><\/h2>

One very familiar ring was spawned some 4.6 billion years ago from a fragmenting cool molecular cloud.<\/p>

Over the next 100,000 years gravity, gas pressure, magnetic fields and rotation flattened this spinning nebula into our nascent Solar System<\/a>\u2019s protoplanetary disc.<\/p>

Peppered with pre-planetary material and anchored by its young T Tauri protostar, the disc stretched out to 200 Astronomical Units (AU) in diameter (where 1AU is the average distance between Earth and the Sun).<\/p>

Another 50 million years saw rising temperatures fuse hydrogen in the star\u2019s core, allowing energy to counteract gravitational contraction and ultimately spawn our Sun.<\/p>

The legacy? A spherical reservoir of trillions of leftover, loosely bound comets known as the \u00d6pik-Oort Cloud<\/a>, stretching 50,000AU to 200,000AU from our main sequence star.<\/p>

For more info on calculating these gargantuan numbers, read our guide on how astronomers measure distance in space<\/a>.<\/p>

\"An
An artist’s impression of the Oort Cloud. Solar System and Kuiper Belt relative sizes not to scale. Credit: MIKKEL JUUL JENSEN \/ SCIENCE PHOTO LIBRARY<\/figcaption><\/figure>

Hills Cloud<\/strong><\/h2>

Like a Russian Matryoshka doll, within this trundles another hypothesised ring, the doughnut-shaped Hills Cloud.<\/p>

Spanning as far as perhaps 30,000AU from the Sun, this swarming disc of icy debris could contain 20 trillion comets<\/a> \u2013 the largest concentration in our neighbourhood.<\/p>

And, along with the outer cloud, host the so-called long-period comets, which have orbits greater than 200 years.<\/p>

Inside this ring, closer to our Sun, lies another: the diaphanous Scattered Disc, home of the short-period comets, which have orbits shorter than 200 years.<\/p>

Once too distant and circling too slowly to be accreted into larger bodies, these icy Scattered Disc Objects are survivors of the solar nebula: a remnant of the molecular cloud from which our Solar System formed.<\/p>

\"Dwarf
Haumea, a dwarf planet in the Scattered Disc, is known to have its own ring system. Credit: IAA-CSIC\/UHU<\/figcaption><\/figure>

Later strewn by a gravitational interplay between the gas giant planets \u2013 primarily Jupiter, Saturn and a migratory Neptune \u2013 these sentinels still exist in a smaller 50-150AU ring defining the Solar System\u2019s frozen outer realms.<\/p>

Zooming in to some 50AU from our Sun, the inner Scattered Disc meets another ring, the outer Edgeworth-Kuiper Belt extending inwards to Neptune.<\/p>

Here dwell three of the five dwarf planets: Pluto, Haumea<\/a> and Makemake, each rolling alongside other smaller orbiting bodies.<\/p>

We meet another narrow dense and newly discovered ring, this time around rugby ball-shaped Haumea.<\/p>

A possible result of a collision between its moons Hi\u2019iaka and Namaka, this ring was discovered occulting distant star URAT1533-1825 in January 2017, double-dimming its light by an astonishing 50%.<\/p>

Solar System planets<\/strong><\/h2>
\"An
An image of Uranus and its rings captured by the Keck II telescopeSource: W. M. Keck Observatory (Marcos van Dam) – Lawrence Sromovsky, University of Wisconsin-Madison\/W.W. Keck Observatory<\/figcaption><\/figure>

Spiralling yet further inward from these Trans-Neptunian Objects \u2013 those minor planets populating the Kuiper Belt, Scattered Disc and Oort Cloud \u2013 we spy Neptune, Uranus, Saturn and Jupiter.<\/p>

Recognise a theme? Yet more rings. Neptune has six, each tenuous and dusty. Uranus, with its arcs and interspersed dust bands, has 13.<\/p>

The most extensive ring system, of course, are Saturn’s rings<\/a>.<\/p>

Sculpted by gravity, resonances between embedded \u2018shepherd\u2019 moons and other phenomena, these rings are exquisite.<\/p>

The water ice Saturn’s rings are made up of have been pushed, pulled and pummelled into spiral density waves, cliffs, accreting moonlets, gaps, spokes and other dazzling derivations.<\/p>

Yet these are but trivial compared to the Phoebe dust ring. This Saturnian circle spreads a whopping 6 to 12.5 million km and is sparsely peppered with dark particles measuring just one-tenth to one-fifth the average width of a human hair.<\/p>

\"Saturn\u2019s
Saturn\u2019s Phoebe dust ring has a diameter the equivalent of 300 Saturns. Credit: NASA\/JPL-Caltech\/SSI<\/figcaption><\/figure>

As we dive ever deeper into our Sun\u2019s gravitational well we discover the lesser-known Jovian rings: a system of 100 to 1,000-year-old self-replenishing dust.<\/p>

Looming 10,000km above Jupiter\u2019s ring plane spins the thick inner torus or \u2018halo\u2019, girdled by an outer razor-thin ring some 30km deep.<\/p>

A third ring\u2019s inner edge furnishes a faint 600km-thick cloud, or bloom, fed by dust from moons Metis and Adrastea, and other impacting bodies.<\/p>

Concentricity continues. The main ring smears into two wider \u2018gossamer rings\u2019, Amalthea and Thebe, so-named after the Jovian moons from whose material they are composed.<\/p>

\"Jupiter,
Credit: Webb NIRCam composite image (two filters) of Jupiter system, unlabeled (top) and labeled (bottom). Credit: NASA, ESA, CSA, Jupiter ERS Team; image processing by Ricardo Hueso (UPV\/EHU) and Judy Schmidt.<\/figcaption><\/figure>

Beyond is the whiff of a primordial arc of dust detected by NASA\u2019s New Horizons probe, hinting at the dawn of yet another ring.<\/p>

And cradling them all is a bagel-shaped torus of ionised sulphur, oxygen, sodium and chlorine.<\/p>

This dynamic hoop centres on Jupiter\u2019s volcanic satellite Io.<\/p>

Io is tilted with respect to Jupiter\u2019s equator and its own orbital plane, and as it completes its 1.8-day orbit, swooping above and below the hoop\u2019s core, neutral atoms and molecules are stripped from its tenuous atmosphere and companion neutral doughnut-shaped cloud.<\/p>

Energised and accelerated by the gas giant\u2019s mighty magnetosphere and speedy 10-hour rotation, this miasmic ring of plasma co-rotates at some 74 km\/s.<\/p>

\"Illustration
Illustration of Chiron and its rings. Credit: Celestia Team – Celestia<\/figcaption><\/figure>

So, just the four gas giant ring-systems then, plus those of tiny Haumea? No! Rings reside almost everywhere in our Solar System\u2019s rubble-ridden realms.<\/p>

Before Haumea\u2019s were discovered astronomers found rings around the 250km-wide asteroid 10199 Chariklo and the 200km-wide minor planet 2060 Chiron.<\/p>

These double-ringed rocky relics orbit between Jupiter and Neptune, their discs diminutive but still beautifully formed.<\/p>

What causes rings to form in the Solar System?<\/strong><\/h2>
\"A
A view of Saturn’s rings captured by Voyager 2, 22 August 1981, from a distance of 2.5 million miles. Credit: NASA \/ JPL-Caltech<\/figcaption><\/figure>

So why are there rings in the Solar System, and why so many? The simple answer is gravity and its governance.<\/p>

This, and competing forces, shaped our nascent Sun and protoplanetary disc. It still does.<\/p>

Any objects orbiting within a planet\u2019s gravitational threshold \u2013 known as the Roche Limit \u2013 endure tidal forces overwhelming their own gravity, which prevents coalescence into a moon.<\/p>

If an orbiting moon breaches that limit, tidal stresses tear it apart. A cosmic impact will rip a moon asunder.<\/p>

There are meteoroid strikes. Cryovolcanic activity creating ejecta. The fallout? Gravitationally corralled rings.<\/p>

\"Artist's
Artist’s impression of an asteroid belt. Credit: Maciej Frolow \/ Getty Images<\/figcaption><\/figure>

This ring-fest overview halts some 2AU from the Sun, in the raggedy bracelet of the main asteroid belt<\/a> circling between Jupiter and Mars.<\/p>

Meet billions more pebbles, larger asteroids \u2013 Vesta, Pallas and Hygiea \u2013 and the 950km-wide dwarf planet Ceres<\/a>.<\/p>

If the Martian moon Phobos smashes into the Red Planet, there will be rubble.<\/p>

Constrained by gravity, it may eternally circle or coalesce into another spherical moon, to be again impacted.<\/p>

Rings represent beginnings, middles and ends, their evolution evident not just around our host star, but others in the Milky Way Galaxy and beyond.<\/p>

\"A
A Hubble Space Telescope image of Mars showing the stages of its moon Phobos’s orbit. Credit: NASA, ESA and Z. Levay (STScI) Acknowledgment: J. Bell (ASU) and M. Wolff (Space Science Institute)<\/figcaption><\/figure>

Solar System rings facts and figures<\/strong><\/h2>

\u00d6pik-Oort Cloud<\/strong><\/b><\/h3>
  • Radius: 200,000AU<\/li>
  • Discovered by Ernst \u00d6pik, Jan Hendrik Oort (theorised)<\/li><\/ul>

    Hills Cloud<\/strong><\/b><\/h3>
    • Radius: 30,000AU<\/li>
    • Discovered by JG Hills<\/li><\/ul>

      Scattered Disc<\/strong><\/b><\/h3>
      • Radius: 100AU<\/li>
      • Discovered by David C Jewitt, Jane Luu (fist object)<\/li><\/ul>

        Edgeworth-Kuiper Belt<\/strong><\/b><\/h3>
        • Radius: 55AU<\/li>
        • Discovered by David C Jewitt, Jane Luu<\/li><\/ul>

          Main asteroid belt<\/strong><\/b><\/h3>
          • Radius: 3.2AU<\/li>
          • Discovered by Giuseppe Piazzi (who discovered Ceres, the first observed object within the belt)<\/li><\/ul>

            Rings of Saturn<\/strong><\/b><\/h3>
            • Radius: 480,000km (outermost)<\/li>
            • Discovered by Christiaan Huygens<\/li><\/ul>

              Phoebe dust ring<\/strong><\/b><\/h3>
              • Radius: 12,500,000km<\/li>
              • Discovered by Anne J Verbiscer, Michael F Skrutskie, Douglas P Hamilton<\/li><\/ul>

                Rings of Jupiter<\/strong><\/b><\/h3>
                • Radius: 226,000km (outermost)<\/li>
                • Discovered by Voyager 1<\/li><\/ul>

                  Rings of Neptune<\/strong><\/b><\/h3>
                  • Radius: 62,900km (outermost)<\/li>
                  • Discovered by Voyager 2<\/li><\/ul>

                    Rings of Uranus<\/strong><\/b><\/h3>
                    • Radius: 51,150km (outermost)<\/li>
                    • Discovered by James L Elliot, Edward W Dunham, Jessica Mink<\/li><\/ul>

                      Rings of Haumea<\/strong><\/b><\/h3>
                      • Radius: 2,287km<\/li>
                      • Discovered by 10 central European observatories<\/li><\/ul>

                        Rings of 10199 Chariklo<\/strong><\/b><\/h3>
                        • Radius: 410km (outermost)<\/li>
                        • Discovered by 10 telescopes in Argentina, Brazil and Chile<\/li><\/ul>

                          Rings of 95P\/Chiron<\/strong><\/b><\/h3>
                          • Radius: 320km (outermost)<\/li>
                          • Discovered by Amanda Bosh, Jessica Ruprecht, Michael Person, Amanda Gulbis<\/li><\/ul>

                            This article originally appeared in the October 2018 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p> <\/body><\/html>\n

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