Names of the Planets

In the beginning…

Most ancient cultures recognized seven “planets” consisting of sun and moon and the five planets visible in the sky. The Latin names of the Planets were simple translations of the Greek names, which in turn were translations of the Babylonian names, which go back to the Sumerians. Some interpretation was required for the Greek, and even for the Babylonian, translations, however. Nergal, for instance, was the god of war but also of pestilence and, especially, the Underworld —overlapping with the Greek Hades. While Kronos was the father of Zeus, Ninurta was the son of Enlil. The Babylonians replaced the Sumerian national gods Enlil and Enki with the patron god of Babylon, Marduk, and his son, Nabû — though Marduk was actually taken to be the son of Enki (called Ea in Babylonian). Ninurta, an obscure god inherited by the Babylonians, may have been identified with Saturn, the slowest moving visible planet, because, at least in one story, he was identified with the turtle. The ancient Egyptian, Sanskrit, and Chinese names for the planets are unrelated to the Sumerian.

The Ancient “Planets”:

English Sumerian Babylonian Greek Latin Egyptian Sanskrit Moon Nanna Sin Selenê Luna Aah or Iah Chandra Mercury Enki Nabû Hermes Mercurius Sabgu Budha Venus Inanna Ishtar Aphroditê Ba’ah or

Seba-djai Sukra Sun Utu Shamash Helios Sol Surya Mars Gugulanna Nergal Ares Mars Heru-deshet Mangala Jupiter Enlil Marduk Zeus Iuppiter Her-wepes-tawy Brhaspati Saturn Ninurta Ninurta Kronos Saturnus Sani

The Chinese names for the true planets are derived from the five elements. The Japanese and Vietnamese probably derived their names for the planets from the Chinese (The Japanese characters are essentially identical to the Chinese although the pronunciation rendered here differs considerably). The Vietnamese word Sao means “star”.

English translation Mandarin Chinese Japanese Vietnamese water star (Mercury) shui3-xing1 suisei Sao Thuy metal star (Venus) jin1-xing1 kinsei Sao Kim fire star (Mars) huo3-xing1 kasei Sao Hoa wood star (Jupiter) mu4-xing1 mokusei Sao Moc earth star (Saturn) dosei Sao Tho

The Chinese also had an earlier set of names from which the Japanese and Vietnamese also derived their earlier names for the planets.

English Chinese Japanese Vietnamese Mercury Shinsei Thàn tinh Venus Tai4-bai2-xing1 Taihakusei Sao thái bach Mars Ying2-huo4 Keiwaku Huynh Hoac Jupiter Sui4-xing1 Saisei Tue tinh Saturn Zhen4-xing1 Chinsei Tran tinh

Ad Astra

Aristarchos of Samos developed an essentially correct theory of a sun-centered solar system surrounded by distant stars, “suns like our own,” in the 3rd century BCE, but his ideas were ignored and mostly forgotten for 2000 years. Then, in the 17th century, great minds like Copernicus, Galileo, and Kepler came to the same conclusions about the true relationships of earth, sun, moon, planets, and stars. With the discovery that the earth orbits the sun, the solar system became, at the same time, simpler and more complex. First, the sun and moon had to be removed from the list of planets and the earth added to it. Then, Sir William Herschel and his sister, Caroline, found Uranus in 1780; Johann Galle and Heinrich D’Arrest discovered Neptune in 1846; and Clyde Tombaugh discovered Pluto in 1930. The International Astronomical Union (IAU) is the body that officially assigns names to celestial objects and continued the tradition of naming the planets for Roman deities for the three “modern” discoveries.

Different languages either use transliterations of the IAU names for the three modern planets or use translations of the official names. Chinese, Vietnamese, and Japanese, for example, use translations. They are:

Translation Chinese Vietnamese Japanese King of Heaven (Uranus) Sao Thiên Vúóng Tennoosei King of the Sea (Neptune) Hai3 wang2 xing1 Sao Hai Vúóng Kaioosei King of the Netherworld (Pluto) Ming2 wang2 xing1 Sao Diêm Vúóng Meioosei

Modern telescopes have discovered planets orbiting other stars and have discovered several bodies orbiting our sun in the Kuiper Belt beyond Pluto. But, oddly enough, there was no official scientific definition of a planet until 2005. The Kuiper Belt discoveries, along with Pluto’s diminutive size, led the IAU to adopt a formal definition of “planet” at their convention in 2005. Here is the IAU resolution:

The IAU...resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

(1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.

(Subsequent debates have clarified that “cleared the neighbourhood around its orbit” refers to the process that happened during the formation of the planets and does not refer to the presence of bodies that later strayed into the orbit after the accretions took place. This interpretation was necessary to resolve the conflict that “if Pluto is not a planet because it has not “cleared its neighbor hood”, then neither is Neptune (because it has not cleared Pluto from its orbital neighborhood) nor Jupiter with the 100,000 or so Trojan asteroids in its orbit nor is the Earth with more than 10,000 near-earth asteroids and other objects in its orbital neighborhood)

The most immediate effect of the new definition was to remove Pluto from the list of solar planets. The howls of protest have not died down, and new discoveries will almost certainly make the new definition obsolete and require its revision. Many of the flaws in the definition have already been identified, among them:

· The definition is far too narrow. It applies only to the bodies in our solar system and does not entirely agree with the accepted criteria for defining extrasolar planets.

· There is no provision for “rogue” planets (those planet-type objects cast out of systems and now free of any star)

· The definition is largely depends on assumptions about how a body is formed whereas the facts are unknown.

o Identifying whether an asteroid was captured or is a left-over from accretion remains “iffy” — largely a matter of many assumptions and guesswork. This is not a good basis for science.

o The latest data from the Stardust mission indicates that planetary formation is far from the neatly organized affair upon which the new definition is based.