Rings of Jupiter

The rings of Jupiter are a system of faint planetary rings. They were the third ring system to be discovered in the Solar System, after those of Saturn and Uranus. The main ring was found in 1979 by the Voyager 1 space probe and studied more in the 1990s by the Galileo orbiter. We have also seen the rings using the Hubble Space Telescope and big telescopes on Earth.

Jupiter's rings are made mostly of dust and have four main parts: a thick inner "halo ring," a very thin "main ring," and two wide, faint outer rings named after the moons Amalthea and Thebe. The dust in these rings comes from moons like Metis and Adrastea, created when objects hit them at high speeds.

The rings look reddish, except the halo ring, which appears blue or neutral. The dust particles vary in size, but the rings contain a lot of tiny pieces around 15 μm across. The total amount of material in the rings is still not well known, but it might be between 10¹¹ and 10¹⁶ kg. Scientists think the rings may have been around since Jupiter formed.

There might also be a small ring or ring arc near the moon Himalia. One idea is that a tiny moon recently crashed into Himalia, and the impact sent material into space to form this ring.

Discovery and structure

Jupiter's ring system was the third to be discovered in the Solar System, after the rings of Saturn and Uranus. It was first seen on March 4, 1979, by the Voyager 1 space probe. The rings have four main parts: a thick inner group called the "halo ring," a very thin and bright "main ring," and two wide, faint outer rings named after the moons Amalthea and Thebe, whose material makes up these rings.

In 2022, studies using computer simulations suggested that Jupiter's rings are smaller compared to Saturn's because of special patterns created by the Galilean satellites that make the rings less stable.

Name	Radius (km)	Width (km)	Thickness (km)	Optical depth (in τ)	Dust fraction	Mass, kg
Halo ring	92,000–122,500	30,500	12,500	~1 × 10⁻⁶	100%	—
Main ring	122,500–129,000	6,500	30–300	5.9 × 10⁻⁶	~25%	10⁷– 10⁹ (dust) 10¹¹– 10¹⁶ (large particles)
Amalthea gossamer ring	129,000–182,000	53,000	2,000	~1 × 10⁻⁷	100%	10⁷– 10⁹
Thebe gossamer ring	129,000–226,000	97,000	8,400	~3 × 10⁻⁸	100%	10⁷– 10⁹

Main ring

The main ring of Jupiter is the brightest part of its ring system. It stretches from about 122,500 kilometers to 129,000 kilometers from Jupiter. This ring was discovered in 1979 by the Voyager 1 space probe and studied later by the Galileo orbiter.

The ring looks different depending on how we view it. In some lights, it appears thin and faint, while in other lights it looks thicker. Scientists think the ring is made of tiny particles and larger pieces, which is why it changes shape in different lights. The ring also has small clumps of particles and waves caused by Jupiter's gravity, which were possibly created when Comet Shoemaker-Levy 9 hit Jupiter in 1994.

Halo ring

The halo ring is the closest and thickest ring around Jupiter. It starts about 122,500 kilometers from the center of the planet and gets thicker as it moves closer to Jupiter. Scientists think it extends up to 10,000 kilometers above and below the main ring plane, though its exact height is not fully known. The inner edge of the halo is sharp, beginning at about 100,000 kilometers from Jupiter's center.

This ring looks brightest when light bounces straight back to the observer. It was studied in detail by the Galileo spacecraft. Though it is fainter than Jupiter's main ring when viewed from the side, it can appear just as bright because it is so thick. The halo ring looks the same whether viewed from the front or the back, but it is generally dimmer from the back. Its color is not red like the main ring and might even appear slightly blue.

Scientists believe the halo ring is made mostly of very tiny dust particles, smaller than 15 micrometers. These tiny particles scatter light in a way that makes the ring appear brighter from the front and bluer in color. The dust in the halo likely comes from the main ring. The halo's large thickness is thought to be caused by the magnetic field of Jupiter affecting the paths of these dust particles.

Gossamer rings

Amalthea gossamer ring

The Amalthea gossamer ring is a very faint ring that stretches from the orbit of Amalthea at 182,000 km to about 129,000 km from Jupiter. It is brightest near its top and bottom edges and gets brighter as it moves closer to Jupiter. In 2002–2003, the Galileo spacecraft passed through these rings and detected tiny dust particles.

Thebe gossamer ring

The Thebe gossamer ring is the faintest ring around Jupiter. It stretches from the orbit of Thebe at 226,000 km to about 129,000 km from Jupiter. Like the Amalthea ring, it is brightest near its edges and gets brighter toward Jupiter. The Galileo spacecraft also detected dust particles here, similar to those in the Amalthea ring.

Himalia ring

In September 2006, NASA's New Horizons mission to Pluto passed by Jupiter for extra speed. During this flyby, it took pictures of what looked like a very thin, unknown ring or part of a ring near the path of a small moon called Himalia. Scientists think this ring might be pieces from a tiny, unseen moon that crashed into Himalia. This means Jupiter may still be getting and losing very small moons through collisions.

Exploration

The rings around Jupiter were first guessed to exist when the Pioneer 11 spacecraft studied the planet's radiation belts in 1975. In 1979, the Voyager 1 spacecraft took a blurry picture of the rings, and Voyager 2 later that year took more pictures to help understand their shape. The Galileo orbiter, which flew between 1995 and 2003, took much clearer pictures and taught us a lot more about these rings. Ground telescopes like the Keck and the HST also studied the rings in the late 1990s and early 2000s. In 2007, the New Horizons spacecraft sent us even finer details of the main ring. The Cassini spacecraft, on its way to Saturn, also observed Jupiter's rings in the year 2000. More missions in the future will help us learn even more.