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Motion of J002E3

  1. Jan 1, 2004 #1

    Ivan Seeking

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  2. jcsd
  3. Jan 1, 2004 #2

    selfAdjoint

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    NASA seems to be content with "object". Some astronomers object to calling every satellite in the solar system a "moon". They want to reserve Moon as a proper name for THE Moon.
     
  4. Jan 1, 2004 #3

    Ivan Seeking

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    The meaning of the word "planet" seems to be a little subjective as well. I once read that the biggest difference between a planet and a moon is that a moon has no atmosphere. Don't a number of "moons" have atmospheres; and doesn’t at least one planet, Pluto, lack any atmosphere?
     
  5. Jan 2, 2004 #4

    Phobos

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    Astronomers still consider the Earth to have 1 moon, even though there are a couple curious nearby objects like J002E3. Note that last paragraph in the second link..."Earth's second one is called Cruithne. It was discovered in 1986 and it takes a convoluted horseshoe path around our planet as it is tossed about by the Earth's and the Moon's gravity. "

    Lots of gray areas in astronomical definitions like this.

    You are correct that that "no atmosphere" is a bad definition of a moon, but maybe presented in a certain context it can get you close enough (e.g., if speaking in general to little kids or if you needed to take a guess on a game show :smile:)

    Saturn's moon Titan has quite an interesting atmosphere (which NASA will be sending a probe into soon...yippee!!). The planet Mercury has no real atmosphere except for the temporary particles the sun blasts off it. Pluto's* thin atmosphere disappears during its "winter" (it freezes and snows down to the surface). Asteroids don't have atmospheres but they are not moons (ok, a few are, like my namesake). Comets have gases surrouding their icy/rocky cores, but they are not planets.

    In general, planets are the large, non-star objects orbiting a star. Moons are the things orbiting the planets. I would guess that Cruithne and J002E3 are not called moons because they're too odd (non standard orbits around the planet).

    * keeping that particular debate of planet-hood (planet-dom?) aside
     
  6. Jan 2, 2004 #5

    Ivan Seeking

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    Is this a situation where the definitions have been forced to evolve due to having better information about these various types of bodies?
     
  7. Jan 2, 2004 #6

    Nereid

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    That's part of the reason; others include nostalgia (a.k.a. history - look at the fuss about whether Pluto is a planet or not), stickiness (also a.k.a. history - 'moon' vs 'satellite'), and the lack of a linguistic dictator (even though the IAU does a pretty decent job of standarisation, not every editor of every relevant peer-reviewed scientific journal is always consistent).
     
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