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."

Comments

The definition of "planet" is universally ...

[B3ryllium]

... agreed to be "Marlon Brando"

A simple rule of thumb:

[AEton]

If someone bothered to name a Roman god after it, it's a planet. Pluto, Mars, Jupiter--all friendly planets.

Alpha Centauri? Bah--probably a reflection off that Hubble thingy.

Re:A simple rule of thumb:

[Da Web Guru]

Well, I guess that someone needs to name a Roman god "Earth"...

Re:A simple rule of thumb:

[kalidasa]

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."

How about "Life sustaining?"

[beernutz]

Wouldn't it make sense to take into account whether the planet could feasibly sustain life too? I mean could a 700km round body in space support an atmosphere?

Re:How about "Life sustaining?"

[Anonymous Coward]

I mean could a 700km round body in space support an atmosphere?

Well, sometimes Pluto has an atmosphere, and sometimes it doesn't. Only when it gets closer to the Sun in it's orbit does it "generate" an atmosphere from sublimation of ice. Later on it evaporates away be due to lack of gravity to hold it there. I doubt we would classify it as a part-time planet. BTW.. comets can have a "pseudo atmosphere" too.

Planet

[blair1q]

Planet: n. Any object orbiting a star, not orbiting a planet, and having a radius greater than the radius of Pluto minus one millimeter.

Why is size an issue?

[Jason1729]

I went to an astronomy talk at the University of Toronto a few years ago. The presenter defined a planet as any celestial body that doesn't radiate light. That explicitly includes asteroids and moons. Why is it necessary to make the distinction between planet and asteroid?

The whole point of the article is to arbitrarily define the distinction which just proves how stupid it is.

Jason
ProfQuotes

Why not set a defined width?

[Jailbrekr]

they say bodies larger than 700km go from being potatoe shaped to round. why not set a defined width above this 'minimum', and anything larger be called a planet? twice the minimum sounds plausible, and that means Pluto would still be defined as planet.

Re:Why not set a defined width?

[aleonard]

Because some moons are larger than Pluto... would they be considered planets?

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/nineplanet s/nineplanets.html )

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.

Bah

[DaLiNKz]

Why do they always need to complicate things. I thought size doesnt matter.

Re:silliness

[1u3hr]

why can't we be content to keep the traditional designations of what make up a planet?

a) this is science, not tradition, scientific terms need an absolute definition.

b) traditionally, you only had the naked-eye planets: Mercury, venus, Mars, Jupiter, Saturn. What do you call the other gas giants? Not to mention, Mercury was thought to be two planets by some (the morning and evening star).

c) my opinion, just set it so that Pluto-size is the cut-off. Anything smaller isn't one. However, in a few centuries when we can detect "planets" in other solar systems this would seem a bit heliocentric, so I can see the Basri's point (in the FA: "Basri's definition, a planet must orbit a star, not another planet, and it must be round. That means it must be 700 kilometres in diameter, when gravity moulds it into a sphere, or bigger.").

This is deeply troubling

[WankersRevenge]

As a representative one of the nine planets, I find this proposal deeply troubling, especially since there are not any other representatives from the other eight. Once a planet is classified as an "asteroid" or "floating piece of shit with gravity", it not only loses its prestige, but also, it cannot apply for federal grants, and hence, usually suffers a major economic blow. Laugh you may, but I've seen planets go from a heavenly body to a drunk spinning horizontal and finally distingrate into an asteroid belt in no time. We must support our planets because if we don't, then who will?

Absolutely moot...

[jtdubs]

This superficial naming convention makes absolutely no difference at all. It has no effect on anything.

It would be like if you changed the biological classification system so that bears were no longer Mammals. What difference does this make to the bears? None. What difference does this make in how we relate to bears? None.

It is simply an arbitrary naming convention. As are all naming conventions.

It reminds me of an old Zen saying that I am likely paraphrasing miserably:

"Before Zen, a mountain is a mountain. While one is practicing Zen, a mountain is no longer a mountain. After Zen, a mountain is once again a mountain."

Justin Dubs

Location Location Location

[infonography]

Just like in Real Estate, it's where it is not how big. The US States of Washington and Alaska have larger Island then Rhode Island. But Pluto is

Alone in it's orbit, it's moons orbits it

isn't too far out

Re: How do you pronounce Quaoar?

[Ozymandias_KoK]

Badly?