Planetary Names

FAS Astronomers Blog, Volume 34, Number 5.

From time to time, we witness a parade of planets across the evening sky. Well, almost. At times, some of the planets are very low in the horizon and difficult to see. But they’re still up there and officially we have eight planets in our solar system. Of course, there are also five official dwarf planets and if you travel farther out into the galaxy, there are over 6,000 known exoplanets. 

Planets

Five of the official planets (Mercury, Venus, Mars, Jupiter, and Saturn) were visible in the night sky and known in ancient times. According to Geminus of Rhodes in Elementa astronomiae (per Thomas Heath), David Southworth, and James Evans, the Greeks named these planets after their characteristics: Stilbon (the gleaming star), Phosphorus (the light bringer or star of Aphrodite), Pyroeis (the fiery star), Phaethon (the bright star), and Phainon (the shining star). The Greeks then assigned gods from their mythology to watch over each planet. It is from here we get the Greek names: Hermes, Aphrodite, Ares, Zeus, and Cronus. 

Evidently, as Raymond Shubinski and John Burnet point out, Venus proved to be a problem. It was initially thought to be two different planets, and they were named Phosphorus (morning) and Hesperus (evening). Eventually, folks figured out that they were one and the same and it became Aphrodite. 

Much later, the Romans kept the same naming convention but converted the names to the Roman (Latin) equivalents: Mercurius, Venus, Mars, Iuppiter, and Saturnus. During the Renaissance, most scientific literature such as Newton’s Principia, were written in Latin, so the Latin names have remained with us, but with an English tweak to them: Mercury, Venus, Mars, Jupiter, and Saturn.

The Earth has a different story. It is not named after either a Greek or Roman mythological god. Rather the name comes from old English (e.g., ertha) and old German (e.g., erde) – words meaning ground or soil. It is also not known who coined the term Earth, except that it has been used for a thousand years or more. 

Everything was fine until William Herschel came along and found a new planet. This was the first one not known in antiquity, so it needed a name. For a time, it was simply referred to as planet Herschel. Herschel, who was born in Germany but emigrated to England, wanted to curry favor with King George III. He, therefore, proposed naming the new planet Georgium Sidus (Georgian Star). This didn’t sit too well with those outside of England. So, Johann Elbert Bode suggested it be named after the Greek god of the sky. Following Bode’s lead and to keep with tradition, Uranus – the Latin version of the Greek Ouranos was chosen. However, it is technically a Greek name and not the Roman equivalent, which evidently is Caelus (the god of the sky from Roman mythology). In the end, Uranus has stuck with us, although it is the only planet with a Greek rather than Roman name. 

There is still a bit of a controversy over how to pronounce the name Uranus. You can find out more about this in a previous article, What’s in the Name Uranus. Although, I was recently asked, is this just an English issue or is there an issue with how to pronounce the name of this planet in other languages? The scientific community generally uses the English names, so I would think the controversy remains, however, I believe they mostly pronounce it “Ur-a-nus.” The name is also spelled Uranus in many languages including French and German, although the pronunciation may be different than the two found in English. Other languages, including Spanish and Portuguese, use Urano, which probably doesn’t have the same problem as the English pronunciation. 

Neptune was discovered next. There is some controversy associated with its discovery. For more, see The Discovery of Neptune. In the end, it was named after the Roman god of the sea – probably because of its blue color. 

In 1930, Pluto was discovered by Clyde Tombaugh at the Lowell Observatory in Flagstaff, Arizona. It used to be a planet. Then, beginning in 2006, it wasn’t a planet anymore. You can find more about both the discovery and reclassification of Pluto in Discovering Pluto and Reclassifying Pluto. After Pluto’s discovery, it needed a name. The folks at the Lowell Observatory had several in mind. However, a young British girl, Venetia Burney, had been reading about ancient mythology and thought the name Pluto, the Roman god of the underworld, was appropriate. Her suggestion made its way to the Lowell Observatory, and the newly discovered “planet” became Pluto. The Disney dog was evidently named later. 

In any event, the planetary names still associate the planet with its characteristics.

• Mercury is the swiftest planet and is named after the messenger god of travel and commerce. 
• Venus is a beautiful bright star in the sky and is named after the goddess of love and beauty.
• Mars, with its reddish color, is named after the god of war.
• Jupiter, the largest planet, is named after the king of gods.
• Saturn, which slowly moves across the sky, is named after Cronus, the father of Zeus.
• Uranus, with a pale blue color, is named for the Greek god of the sky and father of Cronus. 
• Neptune, with a blue color, is named after the god of the sea.
• Pluto, deep in the far reaches of the Solar System, is named after the god of the underworld.

Dwarf Planets

As noted above there are five official dwarf planets and they needed names. We’ve covered Pluto because it used to be a planet. However, the other four have stories as well.

Ceres was discovered in 1801 by Giuseppe Piazzi at the same time as the discovery of the first few large asteroids. However, these new objects weren’t initially called asteroids, and for a time, they were considered full-fledged planets. They eventually found so many of them that they began referring to them as asteroids or minor planets. For more on this, see Discovering Pluto. 

Ceres is the only asteroid large enough to be round, so it was classified as a dwarf planet along with Pluto in 2006. After its initial discovery, Piazzi suggested the name Cerere Ferdinandea for the new object – after the Roman goddess of agriculture (Ceres) and King Ferdinand III of Sicily. But only the Ceres portion remained, and it became just Ceres. It is from this we get the name Cereal for our breakfast food. 

Eris was initially nicknamed Xena after the TV warrior princess. Later, it was officially named after the Greek god of strife and discord. This was a fitting name because, at nearly the same size as Pluto, it was one of the reasons Pluto was reclassified. This brought strife and discord to the solar system as astronomers wrestled with the definition of a planet and the number of official planets. 

Haumea and Makemake were discovered around the same time of Pluto’s reclassification and officially became dwarf planets a couple of years later. They were named by their discoverers based on separate creation myths. Haumea, initially nicknamed Santa, is a goddess in Hawaiian mythology. Makemake, initially nicknamed Easter Bunny, is the creator of humanity in the mythology of the Rapa Nui people from Easter Island in the south pacific.

Moons

Then came the moons – and there are many of them. So, it’s hard to keep up with them all, much less their names. Check with us at “New Moons of the Solar System” for an updated count (with reference to the official list of moons from NASA). 

The Earth’s moon was known back in antiquity – it is hard to miss it in the night sky. For a long time, it was the only moon (as far as we knew). The USGA notes that it has several names, but simply the Moon seems to be the choice in English.

Every civilization has had a name for the satellite of Earth that is known, in English, as the Moon. The Moon is known as Luna in Italian, Latin, and Spanish, as Lune in French, as Mond in German, and as Selene in Greek. (USGA “Planet and Satellite Names and Discoverers”)

In 1610, when Galileo pointed his telescope up at the night sky, he noticed that Jupiter had four “stars” moving in its vicinity. After several nights, he concluded they were moons orbiting the planet. He needed to name these four moons. In many of his writings he simply referred to them as I, II, III, and IV. In addition, he proposed they be named the “Medicean Stars” in honor of his patron the Medici family. However, Simon Marius, who claimed to have observed the moons first, suggested names from Roman mythology and characters associated with Jupiter (Io, Europa, Ganymede, and Callisto). These names were also supported by Johannes Kepler but didn’t catch on for another couple hundred years. Today the four large moons of Jupiter are named as Marius proposed but are also called the Galilean moons after Galileo.

After his discovery of Uranus, William Herschel went on to find its two largest moons in 1787. Herschel, or possibly his son John, chose to name the moons Titania and Oberon – the queen and king of the fairies in Shakespeare’s A Midsummers Night’s Dream. At the suggestion of Herschel’s son John, the next two moons became Ariel and Umbriel from The Rape of the Lock by Alexander Pope. The smaller Miranda is from The Tempest. As other moons were discovered they were also named after characters from Shakespeare.

Triton, the largest moon of Neptune (named after the Roman god of the sea and equivalent of the Greek Poseidon) is the Greek son of Poseidon. Other Neptunian moons have names associated with mythological characters of the sea or water. The moons of Pluto are all associated with the underworld (Charon, Styx, Nix, Kerberos, and Hydra). 

Eris’ one moon Dysnomia is named after Eris’ daughter from Greek mythology. Haumea’s two moons were initially nicknamed Rudolph and Blitzen. They are now officially named after the daughters of Haumea. Hi’iaka is a goddess of the Big island of Hawaii and Namaka is the Hawaiian goddess of the sea. Makemake’s one moon is still referred to as MK1. I guess no one has gotten around to giving it a more formal name.

Today, moons are generally given names associated with their planet and from the mythology upon which the planet’s name is based. To keep everything in order, the International Astronomical Union’s Working Group for Planetary Nomenclature developed official rules about how moons and surface features are named. 

Surface Features

Surface features are also managed by the IAU’s working group. There are too many to discuss them all here, but we can look at a few on Mercury, Venus, Mars, Ceres, Titan, Pluto and its largest moon Charon.

Mercury has a huge 900-mile-wide crater called Caloris Basin. It is likely an impact area that resulted from a collision with a large object some billions of years ago. 

Features on Venus are named for females with three exceptions. Maxwell Montes is the tallest mountain range and is named after James Clerk Maxwell. Alpha Regio and Beta Regio are two highland areas that rise above the Venusian plains and have neutral names.

Mars has several large surface features. Olympus Mons is the largest volcano in the Solar System. It, along with three smaller volcanoes, are located in the Tharsis region. To the east is Valles Marineris a huge 2,500- to 3,000-mile-long canyon discovered by the Mariner 9 spacecraft in the early 1970s. Hellas Planitia and Utopia Planitia are two large lowlands. Of course, we can’t forget the so-called “faces on Mars.”

_{^{“Faces on Mars.” Images Credit: NASA/JPL/Malin Space Science Systems.}}

Ceres has a couple interesting features that were discovered by the Dawn spacecraft back in 2015. There are two white spots that astronomers think might be composed of salt. Officially they are Cerealia facula and Vinalia facula located within the Occator Crater. There is also an interesting looking mountain called Ahuna Mons.

Saturn’s largest moon Titan is covered by a thick hazy atmosphere. However, if we can peer through the atmosphere, we find a surface composed of rock-hard water ice along with rolling dunes. There are also seas filled with liquid methane at Titan’s northern pole (Kraken, Ligeia, and Punga Mare). A smaller lake, Ontario Lacus, is found at the southern pole. Two large areas are situated along Titan’s equator. Shangri-La is a dark-colored lowland filled with flowing dunes. Xanadu is a light-colored plateau of ice with mounds and knolls extending above the ground (hummocky).

The most noticeable feature on Pluto’s surface is a heart shaped area that is filled with frozen nitrogen. Officially it is Tombaugh Regio (named after Pluto’s discoverer Clyde Tombaugh). The western portion is called Sputnik Planitia (named after the first artificial satellite). Another is a dark area filled with Tholins (organic gunk). It was initially (and unofficially) named Cthulhu Regio but is now officially Belton Regio (after astronomer Michael Belton). 

Many of the surface features on Charon were unofficially named after science fiction references. These included Kirk, Spock, Sulu, and Uhura craters as well as Tardis Chasma and Gallifrey Macula. A dark area, filled with Tholins that carried over from Pluto, was initially referred to as Mordor Macula. However, most of these names have yet to be officially adopted and surface features now have more acceptable (mundane?) names.