# Classification of a Comet

Google's definition of a comet is:

a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun.

This doesn't cut it for me. Neither does wikipedia's similar entry.

It pertains to the sun, even though comets are present in other parts of the galaxy other than the solar system and probably other galaxies.

Whats more dwarf planet can be classified as follows:

 * orbits a host star
* rounded by its own gravity
* not massive enough to induce thermonuclear fusion
* not massive enough to clear its region of debris


Which pretty much fits the bill of a comet.

Do you think the following is a fair / recognised classification of a comet:

Comet:
* not rounded by its own gravity
* not massive enough to induce thermonuclear fusion
* not massive enough to clear its region of debris
* composition of ice and dust


But then that's pretty similar to an asteroid:

Asteroid:
* not rounded by its own gravity
* not massive enough to induce thermonuclear fusion
* not massive enough to clear its region of debris


However, this means if an asteroid is comprised of ice and dust, it becomes a comet?

Or are asteroid never comprised of ice and dust? Does my asteroid classification need beefing up, regarding an asteroid's composition?

I'm feeling the comet and the asteroid both need some classification pertaining to their orbit as well? Though thats tricky because only some comets and asteroid, so they're similar in that regard as well! Maybe more details on each objsts composition is needed, like I say...

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Cross-posted to physics.stackexchange.com/q/127181/2451 – Qmechanic Jul 30 '14 at 14:36

You've answered your own question there, the difference between the two is that asteroids are rock whereas comets are made up of ice and dust. An asteroid doesn't heat up when it gets close to the Sun and doesn't produce a tail. Comets can orbit the Sun or any star in a long elliptical (Comet West) or short elliptical (Comet Encke 3.3 Years) period whereas asteroids are found in the Asteroid Belt between Mars and Jupiter and in the Kuiper Belt. Sedna is a long period asteroid further out any other object in the solar system but it is still an asteroid according to what we know. https://www.universeguide.com/fact/comets https://www.universeguide.com/fact/asteroids

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