The Oberon moon is one of the five major moons of Uranus. From facts and figures to its Shakespearean name, let us learn more about this major moon of the “sideways planet.”
What is Oberon?
Oberon is one of the 27 moons of the planet Uranus. It is also called Uranus IV. This moon was discovered in 1787 by William Herschel, the same person who discovered Uranus just six years before. More information was gathered about it in January 1986 when Voyager 2 approached the closest to the natural satellite. No magnetic field and atmosphere were detected from it.
The southern hemisphere of Oberon was facing the Sun during the flyby. The northern hemisphere, on the other hand, was in the dark so it was not observable. The Voyager 2 probe was the only close encounter we had with Oberon and the whole system of Uranus. Its nearest approach to Oberon was approximately 470,600 km.
Nowadays, with the help of the advancement of technology, it is now possible to see Oberon using large amateur telescopes.
The natural satellites of Uranus are categorized into three groups: the smaller inner moons, the five major moons, and the outer irregular moons.
Moons Of Uranus
One can easily remember the moons of Uranus because they are named after certain literary characters. Most of them are from the works of William Shakespeare while some were inspired by that of Alexander Pope’s works.
It was the son of its discoverer, John Herschel, that named the moon Oberon. The name was after Oberon, the king of the fairies, from one of the most famous plays of Shakespeare, A Midsummer Night’s Dream.
One explanation for the formation of Oberon is that it was born from Uranus’s accretion disc. This disc is made up of gas and dust which may have originated from the formation of Uranus.
Another possible origin of this disc is that it may have formed from a big impact that largely affected Uranus, resulting in its large axial tilt. This tilt has a big impact on the seasons of this planet. Its northern and southern poles are either bathed in total darkness or perpetual sunlight for 42 years straight. It has one of the most extreme seasons in the solar system.
Location of the Oberon Moon in the Solar System
Oberon is just one of the many Uranian moons. Getting to know Oberon also means knowing the basics of Uranus. One year on this world is 84 years here on Earth, that is about the entire human lifespan.
Uranus is 1.8 billion miles away from the Sun or roughly 2.9 billion kilometers. That distance translates to 9.8 astronomical units (AU). Remember that one astronomical unit is the distance from our planet, Earth, to the Sun.
While most of the planets rotate from west to east, including the Earth, Uranus does otherwise. It rotates from east to west just like Venus.
The first four moons discovered in Uranus were Titania, Oberon, Ariel, and Umbriel. William Lassell called Oberon Uranus II before. However, in 1851, he assigned their Roman numerals designation according to their distance from the planet they are orbiting.
With that said, Ariel is Uranus I, Umbriel became Uranus II, followed by Titania which is Uranus III, and Oberon is Uranus IV. Many years later in 1948, the moon Miranda was discovered. It became Uranus V, though it has the closest orbit among the five large moons.
Oberon, however, remained the outermost moon among the five.
Characteristics of Oberon
Surface Color: Red
Composition: Ice and rock
Radius: About 761.4 km
Surface Area: 7,285,000 sq. km
Orbit: 584,000 km from Uranus
Orbital Period: 13.5 days
Rotational Period: 13.5 days
Mass: 2,883,438,065,279,000,000,000 kg
Apparent Magnitude: 14.1
Oberon has a dark and slightly red appearance. Because it has the same orbital and rotational period of 13.5 days, it is tidally locked to Uranus. With synchronous rotation, only one of its sides faces the planet all the time. It orbits Uranus in the equatorial plane together with the other moons. That is because the blue-green planet orbits the Sun on its side.
Oberon is made up of water ice and a dense component likely to be of rock and carbon material. A small percentage of frozen volatile materials may also be present.
Oberon has a rocky core which is contrasted by an icy mantle. There may be a liquid ocean layer between the two layers if the ice contains antifreeze like ammonia.
The radius of Oberon is approximately 761.4 km which equals about 0.1194 Earths. A slight eccentricity of 0.0014 is observed in this moon, and its inclination to the equator of Uranus is 0.058°.
Oberon has a surface area of 7,285,000 sq. km. Its orbit is about 584,000 km from its planet. It is the farthest from Uranus among the major moons. With that, part of the orbit of Oberon is outside the magnetosphere of Uranus.
The mass of Oberon is 2,883,438,065,279,000,000,000 kg. It has an apparent magnitude of 14.1, too faint to see with the naked eye for observers here on Earth. The Bond albedo of Oberon is around 14%.
From the surface, this natural satellite can be described as an old moon with many craters. These features seem primarily formed by the impacts of asteroids and comets.
One common thing about these craters is the presence of a dark material that is yet to be identified. Some of the craters of Oberon even measure 210 km across. This moon, in itself, has minimal internal activity.
Surface Features of Oberon
Oberon is perhaps the oldest among the moons of Uranus. It can be easily distinguished by the many large craters on its surface. In fact, it has the most craters among all the moons of Uranus. Their presence is an indication of the many encounters it has in the past.
The two geological features of Oberon are its craters and chasmata.
Usually found on a planet, moon, or other solid body, an impact crater is a small circular depression. The other one is a chasma (or chasmata in plural). It is characterized by a deep and elongated depression, comparable to a canyon here on Earth.
Oberon’s surface is unique, bringing together science and literature. There are ten named features on the known parts of this moon.
Nine of the distinct marks of Oberon are craters, each named after male characters from the literary works of William Shakespeare. The other one, which is a chasma, is also inspired by the comedy A Midsummer Night’s Dream. The name was not explicitly mentioned in the play, however, but appeared in French folklore.
The largest of the craters of Uranus is Hamlet which is 206 km in diameter. It is followed by Macbeth which is 203 km across. The smallest crater is Mark Anthony, measuring 47 km across.
Below is the list of Oberon’s craters:
Another prominent feature of Oberon is its largest canyon called Mommur Chasma. The formation of this steep-sided depression is believed to have formed because of the expansion of Oberon. This expansion caused its ice crust to crack thus forming the canyon-like feature on the moon’s surface. Mommur Chasma has a diameter of 537 km.
Oberon Moon – Additional Facts
- Voyager 2 is the only close encounter we have with Oberon which took the only available close-up images as seen on NASA’s website. This probe photographed about 40% of this moon. However, only 25% of it allows geological mapping.
- Oberon appears to be the reddest of the five main moons of Uranus.
- Oberon ranks as the second-largest moon among the 27 Uranian satellites.
- Umbriel is the darkest major moon of Uranus while Oberon is the second. They are somewhat similar but Oberon is larger than the other by about 35%.
- Oberon ranks ninth on the list of most massive moons of the Solar System. Taking the first spot is Jupiter’s moon, Ganymede. It is followed by Titan (Saturn), Callisto (Jupiter), Io (Jupiter), Moon (Earth), Europa (Jupiter), Triton (Neptune), and Titania.
- Oberon was discovered on the same day that William Herschel discovered Titania, the largest moon of Uranus.
- Sunlight reaches the Uranian system in about 2 hours and 40 minutes.
- The tilt of Uranus is nearly at a right angle in relation to its orbit. This may have been a result of a collision it had in the past with an object with a size comparable to the Earth.
- Voyager 2 is a twin spacecraft to Voyager 1. Their original mission was to make in-depth and close-up observations of Jupiter and Saturn. Their solar system exploration has been so successful that they have explored past Uranus and are still sending information for more than 40 years after they launched!