Planet Definition Doesn't Apply Beyond Solar System

Discovery News ^ | Tuesday, January 26, 2010 | Ray Villard

[SunkenCiv]

According to a strict interpretation of the IAU definition of a planet we're stuck with eight major planets in the entire galaxy. No, wait, the entire freaking universe! No more, no less. Not ever, not never.

Why? Because the IAU definition ignores the over 400 planets to date that have been found orbiting other stars. This month alone 25 new exoplanets were announced at the meeting of the American Astronomical Society in Washington D.C.

The dirty little secret is that the Pluto-antagonists needed the vote of the exoplanet research community to pass their Pluto-is-not-a-planet resolution. Therefore they steered clear of making any judgments whatsoever about anything dealing with the practical infinity of worlds around the 100 million other stars in our galaxy.

My colleague Marc Buie of the Southwest Research Institute in Boulder, Colorado -- a lifelong Pluto hugger and top researcher -- emphasizes that as of today, we do not have a "planet definition" that could work for objects elsewhere in the universe.

[SunkenCiv]

"To Pluto And Far Beyond" By David H. Levy, Parade, January 15, 2006 -- We don't have a dictionary definition yet that includes all the contingencies. In the wake of the new discovery, however, the International Astronomical Union has set up a group to develop a workable definition of planet. For our part, in consultation with several experienced planetary astronomers, Parade offers this definition: A planet is a body large enough that, when it formed, it condensed under its own gravity to be shaped like a sphere. It orbits a star directly and is not a moon of another planet.

[SunkenCiv]

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[DannyTN]

"We don't have a dictionary definition yet that includes all the contingencies."

We don't even know what all of the contingencies are yet. But I would think that the same definition we use for our own solar system would be used for other solar systems, until an object is found that just doesn't fit. Or until a natural dividing line is found that makes redefining "planet" again for all solar systems.

[GeronL]

ugh

[JoeProBono]

[GeronL]

dictionaries stop at ‘oral sex’

[freedumb2003]

“Satellite” should work, no matter what.

[centurion316]

I’m hoping that the President will address this alarming state of affairs in tonight’s speech. I’m afraid that we are all doomed if he doesn’t.

[Cacique]

btt

[HighWheeler]

“We don’t have a dictionary definition yet that includes all the contingencies.”

— — —

The definition of “planet” was determined in 2006 by idiots at the International Astronomical Union (IAU). They said that (in the Solar System) a planet is a celestial body that:

1.is in orbit around the Sun,
2.has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3.has “cleared the neighbourhood” around its orbit.

#3 creates a HUGE problem because Pluto crosses the orbit of Neptune and is actually closer to the Sun than Neptune for 20 years at a time (out of 165 year long orbit). So the problem with rule #3 is that Neptune hasn’t “cleared its own neighborhood” so it shouldn’t be a planet either!

[SunkenCiv]

That refers only to the *known* contingencies. :’)

[SunkenCiv]

:’) Thanks, I needed that!

[decimon]

Planet Definition Doesn't Apply Beyond Solar System

Let's cross that bridge when we come to it. Not count our planets before they hatch. Not go the whole nine orbs. Let's call the whole thing off.

[SunkenCiv]

LOL!

[SunkenCiv]

Not one of Ira’s best. :’)

[GeronL]

Planet definitions and gender definitions seems to have a lot in common. Some people think there are only 2 types and some people think there are gay planets and bi-worlds and more.

[EBFrogger]

When does Neptune collide with the rock formerly known as Pluto?

[PIF]

Definition: Planet

A body orbiting a sun or transiting interstellar space that does not contin humans...

[mowowie]

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970326c.html

[BenKenobi]

They are in 2:3 orbital resonance. Won’t ever happen.