what is a planet?

Answer 1

jeez, i wish i knew, so to speak. astronomers are trying to define the word planet, but it isn't easy. the iau plans to publish the definition in the beginning of september 2006.

watch this space:
http://www.iau.org/NAMING_PLANETS_AND_SEDNA.239.0.html

Answer 2

Defination:- The word planet is derived from the Greek languge in which planets means wanderers. Indeed, they are wanderers around the sun. A general defination of planet is: a planet is a body of considerable mass that orbits a star and that produces no energy through nuclear fusion.


A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star. A mass that becomes massive enough to undergo nuclear reactions is considered a star, not a planet. Based on historical consensus, the International Astronomical Union (IAU) lists nine planets in our solar system. However, since the term "planet" has no precise scientific definition, many astronomers contest that figure. Some say it should be lowered to eight by removing Pluto from the list, while others claim it should be raised to ten or even higher depending on how planets are categorized.

Answer 3

A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star. A mass that becomes massive enough to undergo nuclear reactions is considered a star, not a planet. Based on historical consensus, the International Astronomical Union (IAU) lists nine planets in our solar system. However, since the term "planet" has no precise scientific definition, many astronomers contest that figure. Some say it should be lowered to eight by removing Pluto from the list, while others claim it should be raised to ten or even higher depending on how planets are categorized.

If you want info on PLANETARY FORMATION, go here:
http://en.wikipedia.org/wiki/Planet#Planetary_formation

Hope this helped =)

Answer 4

What makes a planet a planet? Is it the mass? Diameter? Orbit? Distance from the sun?

I would say that the following are minimum characteristics of planets.

1 & 2 below are arbitrary, you may prefer other variables.

1. Minimum Mass. 10^20 Kg. (about 1/100th the mass of Pluto).
2. Minimum Diameter. 1,500 Km (about 900 miles)
3. Orbit. Must be in orbit around a sun, and not a planet (therefore, Luna is not a planet, even though it's larger than Pluto).
4. Distance from sun. Not relevant, as long as it is clearly in orbit around the sun. Therefore, a massive sun may have planets dozen's of light-years away.
5. Is not itself a sun. That would be a binary or higher system.
6. Must not be in interstellar space, not associated with a sun or suns.
7. Not in a field of other bodies with the same approximate orbit. That would leave out anything in the Asteroid Belt and Oort Cloud.


Now, how about "Xena" (aka, 2003 UB313)? To Hades (Greek God of the underworld) with conventions for naming planets. Xena is perfect. And Gabrielle for the moon.

Answer 5

A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star.
The definition of planet has proven elusive despite it being one of the best-known terms in astronomy. The term planet has existed for thousands of years, not only in science but as part of wider culture, applied in its long history to everything from divination to environmentalism. That the solar system consists of nine planets is a widely-held and often repeated idea. To date, however, no actual scientific definition of the word "planet" exists. Until the beginning of the 1990s, there was little need for a definition, as astronomers had only a single sample within the solar system to work from, and the sample was small enough for its many irregularities to be dealt with individually.
However, since 1992 and the discovery of myriad tiny worlds beyond the orbit of Neptune, the size of the sample has risen from nine to at least several dozen. Following the further discovery of the first extrasolar planet beyond our solar system in 1995, the number of samples is now approaching hundreds. These new discoveries have not only increased the number of potential planets, but, in their variety and peculiarity (some large enough to be stars, others smaller than our Moon) challenged long received notions of what a planet could be.
The issue of a correct definition for planet came to a head in 2005 with the discovery of the trans-Neptunian object 2003 UB313, a body larger than the smallest accepted planet, Pluto. The International Astronomical Union, or IAU, which is the body responsible for resolving issues of astronomical nomenclature, has stated that it intends to release its final decision on the matter in September 2006.

Answer 6

A planet is a star that had a little too much cosmic dust mixed in while it was being created. The excess dust towards the surface was too far from the nuclear activity towards the center to heat up or to be heated by compression so it remained cool. The cool surface then cooled more of the planet causing its cooler crust to become thicker.

Answer 7

Good question, and a hot topic in astronomy at the moment. The International Astronomical Union are debating this subject at the moment. There is a very good chance that Pluto will be "relegated" to a planetoid (bigger than an asteroid, but not as big as a planet)

Answer 8

A planet is a body orbiting a star

Answer 9

What indeed? That's a hot topic right now. If other Ort Cloud objects, like Pluto, are found that are the same size as Pluto, should they be a new planet? What about large, gassy objects that don't even orbit stars?

Answer 10

Hot clouds of gas in space spin together and wrap up . . . like cotton candy or yarn when it's spun on a stick. A big bulge forms in the middle of the "stick" or axis and eventually the bulge draws in tighter and tighter until it stays together as a round ball, burning, spinning and cooling down through millions of years. We call those creations, "Suns". When all that spinning gas is still hot, pieces of the gas can spin off like small blobs, and, they too, continue to spin in orbit around their sun for a long time and cool down. Those blobs are planets.