Neptune's Rings

Image of Neptune's Rings taken from Voyager 2 in 1989.

Three rings are easily seen in this image: Adams (outermost), Le Verrier (middle) and Galle (inner ring). To the left of the image, in the Adams Ring, Galatea is visible. Between Adams and Le Verrier, two faint rings can be made out: Arago and Lassell.

Image Credit:

NASA/JPL/Voyager

 

Neptune has five main rings: Galle, Le Verrier, Lassell, Arago, and Adams, named after five important astronomers in Neptune's history. Much like the rings of Uranus, the rings of Neptune are made up of dust particles, and kept in place by shepherd moons, which include Galatea (Adams Ring) and Despina (Le Verrier Ring). It is believed that Neptune has other moons which help keep the rings narrow and stable (so to speak), but they have yet to be discovered.

The Adams Ring is unique in that it contains arcs, which are caused by gravity from Galatea. The arcs were discovered when Neptune occulted a star and where the rings should have been, the star shone through the rings. Close ups by Voyager confirmed that the Adams Ring contained arcs.

Much like the rings around Jupiter, Saturn, and Uranus, the material in the rings of Neptune are not permanent. They are continuously replenished by collisions with the moons of Neptune and are kept in orbit by shepherd satellites. The rings themselves are mostly dust with some ice particles and are covered in organic material (carbon compounds) that make them dark.

Image Credit:

Sky and Telescope

The Moons of Uranus

The Moons of Uranus from closest to farthest starting from the left

Image Credit:

NASA/Voyager

Uranus has 27 known moons which are mostly icy bodies similar to comets. Most of them might be captured comets from the Kuiper Belt or the Oort Cloud. However, there are a few that are considered planetary mass bodies, which means they have enough mass to be differentiated and spherical in shape. Most likely, these five major moons were probably formed at the same time as Uranus.

Titania

Image Credit:

NOAA

Titania has the largest diameter of all of the moons of Uranus, but it is still smaller than our Moon. Its diameter is 1600 km, compared to 3500 km for the Earth. Even though it has the largest diameter, it is not the most massive. That honor goes to Oberon which will be discussed later. Of the five major moons, it is the fourth out from Uranus and has an inclination of 0.34°, meaning it orbits along the equatorial plane of Uranus. William Herschel discovered Titania along with Oberon in January of 1787. Observations of Titania with telescopes and with the Voyager probes tell us a lot of Titania. We know that the moon has two main layers, and icy crust/mantle and a rocky core. The surface is heavily cratered, though not as much as Oberon which also tells us that it was more active in the past than Oberon. Titania was named after the Queen of the Fairies in William Shakespeare's A Midsummer's Night Dream.

Oberon

Image Credit:

NOAA

Oberon has the largest mass, and is second to Titania in diameter. It is also the farthest of the major moons. Discovered at the same time as Titania, Oberon was named after the King of the Fairies in A Midsummer's Night Dream. It is the most heavily cratered moon orbiting Uranus and much like Titania, it has a icy crust/mantle with a rocky core. With an inclination of only 0.058°, it is almost completely aligned with Uranus' equator.

Umbriel

Image Credit:

NOAA

Umbriel is the third largest in mass and diameter of the moons, but was not discovered until 1851 by William Lassell. Like Titania and Oberon, it is an icy and rocky body with an inclination of 0.128°. It is the second most cratered body but went under internal geologic processes in its past to give it the surface it has now. It was named after a character in Alexander Pope's The Rape of the Lock.

Ariel

Image Credit:

NOAA

Ariel is the fourth largest moon and second closest. It was discovered with Umbriel by William Lassell. Again, it is an icy and rocky body that formed in the accretion disk around Uranus based on its inclination of 0.260°. It is also tidally locked in the same way the Moon is tidally locked to Earth. Its name comes from two sources: Pope's The Rape of the Lock and Shakespeare's The Tempest.

Miranda
Image Credit:
NOAA
The last and smallest major moon is Miranda, which is also the closest to Uranus. It is also tidally locked to Uranus and was the last one discovered. Gerard Kuiper (after whom the Kuiper Belt is named - we'll discuss the Kuiper Belt later) found Miranda in 1948. Voyager imaged Miranda as it passed by the Uranus system and discovered that it is the most geologically active because it is the closest and tidal forces keep the interior warm enough. It has the highest inclination at 4.232° and was named after a character in Shakespeare's The Tempest.