What is the criteria that determines what is a planet?

Question

This is a serious question in one of my classes and it would be great if somebody could give me insight on how they classify a what is a planet and what isn't.

Answer 1

the international astronomical union defined three terms "planet", "dwarf planet", and "small solar system body".

a plant must be round and orbit the sun in an isolated orbit. the planets are mercury, venus, earth, mars, jupiter, uranus, and neptune.

a dwarf planet must be round but orbit the sun with a bunch of similar bodies with similar orbits. three of the dwarf planets are ceres, pluto, and 2003 UB313. many more will be added to this list in a short time.

(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 neighborhood 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 neighborhood around its orbit, and (d) is not a satellite.

(3) All other objects orbiting the Sun shall be referred to collectively as "small solar system bodies".


look here:
http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html

Answer 2

The International Astronomical Union (IAU), the official scientific body for astronomical nomenclature, defines "planet" as a celestial body that:[1][2]

(a) is in orbit around a star or stellar remnants;
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape;
(c) is not massive enough to initiate thermonuclear fusion of deuterium in its core; and,
(d) has cleared the neighbourhood around its orbit.

Our solar system is considered to have eight planets under this definition: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Three bodies which fulfill the first three conditions but not the fourth are now classified as dwarf planets: Ceres, Pluto and 2003 UB313. There have been more than two hundred planets discovered orbiting other stars to date.

Before the adoption of a recent resolution, there was no scientifically specified definition of "planet", although various notable astronomers had made proposals as part of the ongoing debate. Without a definition, the solar system had been traditionally seen as having various numbers of accepted planets over the years. It remains to be seen whether the new definition will become universally accepted both within the astronomical community, where there has been significant opposition to the recent adoption, and in the eyes of the greater public.

http://en.wikipedia.org/wiki/Planet

Answer 3

A planet has to:

1. Be massive enough to pull itself into a nearly round shape
2. Have cleared the area in its orbit.

(There are two other requirements: It can't be a star, and it must be orbiting a star. Both of these are simple and neither is really debatable.)

As an example, Earth is mostly round, and there are no large rocks in Earth's orbit. This is why it is considered a planet. Ceres has not cleared the asteroid belt, which is why it is not considered a planet.

Answer 4

Im in astronomy also. The true defiintion of a planet is a moderately large object that orbits a star. B/c ther are no min and max sizes astronomer soften disagree about what is and is not a planet.

Answer 5

a) Must orbit the Sun, not something else that orbits the Sun (in other words, moons don't count)
b) Must be massive enough such that its self-gravity causes it to be spherical
c) Must be gravitationally dominant in its region

These are paraphrases (my own) of the actual International Astronomical Union's definition, which you can look up, of course.

Mike Brown, who discovered 2003 UB313 ("Xena") wrote up a nice explanation about what is and what is not a planet, specifically about the third point that deals with having cleared out its orbit. It's very well written and I strongly encourage you to read it, as I think it addresses your question quite nicely: http://www.gps.caltech.edu/~mbrown/eightplanets/

Answer 6

I heard for example Pluto isn't a planet because it is mostly made of ice. So that qualifies as an astroid or something like that

Answer 7

They just changed it: It think it's
A) Round
B)Gravitationally dominant in its area. (basically its orbiting the sun and nothing else is influencing it orbit. I believe this is why Pluto is getting the ax.)

Answer 8

it has to be round and it has to have a Starbucks.