Slashdot Mirror
Defining "Planet"
beardoc writes "The Sydney Morning Herald is running a story today about a controversial proposal to define what size a planet might be - depending on what the final definition of how big a planet is, we could end up losing Pluto (at 2300 kilometres) to the status of "asteroid" or gaining three more planets - Quaoar, Varuna and Ceres."
Because some moons are larger than Pluto... would they be considered planets?
t s/nineplanets.html )
Diameters:
Pluto: 2274km
Charon: 1172km
Ganymede (orbits Jupiter): 5262km
Callisto (same): 4800km
Titan (orbits Saturn): 5150km
Triton (orbits Neptune): 2700km
Earth: 12756km
Moon: 3476km (Yes, our Moon is larger than Pluto)
Mars: 6794km
Deimos (orbits Mars): 12.6km
Phobos (same): 22km
(all figures courtesy http://seds.lpl.arizona.edu/nineplanets/nineplane
In other words, simple definitions based on size are inadequate. Also, since they're debating whether or not Pluto is a planet, the criteria that it orbits the sun may also be inadequate.
A planet is something which: orbits a star AND is round AND is larger than an arbitrary size AND.. what? The above criteria still allows for a lot of things to be planets that aren't.
We know so little about massive, non-solar bodies outside our solar system. Let's do a little more research on them before we start redefining things.
"In the end they will lay their freedom at our feet and say to us, 'Make us your slaves, but feed us.'" -Dostoevsky
The most common Latin word for "Earth" is Terra, the name of the goddess of the Earth. That's right, Terra. She is I believe almost exactly analogous to Gaia.
Gaia is Greek; another Greek form of the name is "Ge." She is a major early goddess (early meaning pre-Olympian).
"Tellus" is Latin for "land" or "earth," including the concept of Earth as a planet. The name is used for a goddess; that -us ending is not the same one you know from "alumnus," but is feminine 3d declension, and forms its plural as "Tellures." I don't know how it relates to "Terra" or "Gaia" (most educated Romans knew Greek as a second language).
Quaoar, Ceres, and Varuna are all the names of gods or goddesses. Varuna is a Hindu god, of rain, I believe, and so a type of creator god; Quaoar, a native American creator god (IIRC); Ceres is the goddess of agriculture in Roman mythology (she is called Demeter in Greek; the long Homeric poem Hymn to Demeter is the centerpiece of her myth; her daughter Persephone might be familiar to SF fans).
Ceres is also the patron goddess of Sicily, and her discoverer was G. Piazzi, a Sicilian scientist. It was given such an important name (Ceres was a major goddess) because it was assumed, from the application of Bode's "Law," that there must be a planet between Jupiter and Mars, and when Ceres was found, it was at first trumpeted as a planet. However, when the asteroids named after Juno (=Hera, the queen of the Gods), Pallas (=Athena, the goddess of wisdom, warfare, etc.), and Vesta (~Hestia, the goddess of the hearth and home, more important to the Romans than to the Greeks - you've probably heard of the Vestal Virgins, the priestesses of Vesta who kept the eternal flame going in her temple and took an oath of chastity they were executed for violating) were all found in roughly similar orbits, they were reclassified as not "planets" but "asteroids."