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Q: astronomy - planet ( Answered 4 out of 5 stars,   2 Comments )
Subject: astronomy - planet
Category: Science
Asked by: albing-ga
List Price: $4.00
Posted: 12 Jun 2006 18:26 PDT
Expires: 12 Jul 2006 18:26 PDT
Question ID: 737640
what is the distinction between an asteroid and a planet?
Subject: Re: astronomy - planet
Answered By: livioflores-ga on 12 Jun 2006 22:30 PDT
Rated:4 out of 5 stars

The definition of planet is quite subjective, and it takes into
account the size of the object; the classification for planets has
relied on size: objects larger than Pluto are classified as planets.
Nowadays there is a controversy regarding Pluto, because its size and
its particular features.
Better than me, some sources illustrate this case very well:

"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. The name comes from the Greek term ????????, plan?t?s, meaning
"wanderer", as ancient astronomers noted how certain lights moved
across the sky in relation to the other stars. 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."
From "Planet - Wikipedia, the free encyclopedia":


"The definition of planet is mostly a historical distinction. Planets
must be orbiting the Sun (or another star), and must be "large,"
whatever that means. Beyond that, there are no parameters -- after
all, there are only 9! Historically, things have been called planets,
and we stick to that. Some astronomers think Pluto should not be
called a planet because it doesn't qualify in their minds as "large"
and it has a weird orbit. Really, though, it's just a label."
From "Curious About Astronomy: What are the requirements for being a planet?":

See also:

"ASP: A Good Definition of the Word "Planet": Mission Impossible?  - 
Looking (it) Up":

"ASP: A Good Definition of the Word "Planet": Mission Impossible?  - 
The Problem with Pluto":

The following articles could be useful to you:
"Curious About Astronomy: Are Kuiper Belt Objects asteroids? Are large
Kuiper Belt Objects planets?":

"Asteroid - Wikipedia, the free encyclopedia":

Search strategy:
Searched at for:  planet asteroid difference
Searched at Wikipedia for: planets, asteroids

I hope this helps you. Feel free to request for a clarification if you need it.

albing-ga rated this answer:4 out of 5 stars
Thanks.  That works for me.

Subject: Re: astronomy - planet
From: mongolia-ga on 12 Jun 2006 18:51 PDT
Good Question. Technically none but if astronomers are going to not
get their "knickers in a twist" over what is and what is not a planet
they are going to have to define a diameter (probably equal to or
somewhat smaller than Pluto's diameter) above which any body is
considered a "proper planet".

Below that diameter well its just a silly asteriod (or even worse a
non descript rock)


Subject: Re: astronomy - planet
From: oneryt-ga on 15 Jun 2006 22:58 PDT
I figured it would be worthy to note that currently NASA has a mission
"New Horizons" underway, where they have a rocket going towards Pluto.
They launched the rocket at a very good oppurtunity, one which will
not present itself for a very many more years to come. As it is, the
rocket will be able to use the gravitational force of saturn etc. to
get to Pluto much faster then it normally would. The purpose of this
mission, is of course to verify if Pluto is indeed a planet.
Afterwards they plan on guiding it into the outer asteroid belt which
surrounds our Galaxy "Milky Way".

Here is a few links regarding the mission:

Mission overview:

Current Position of rocket:


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