Quote:
Originally Posted by NeilBlanchard
Pluto is smaller than our moon.
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Yes. But does that matter?
Ganymede is bigger than Mercury, and Mercury has no moons.
Pluto does have moons; its biggest,
Charon, has 1/8 of the mass of Pluto and is the 8th biggest moon in our solar system (not counting Pluto or Mercury in as moons).
And that link to Charon has a nice dig into the subject:
Quote:
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In a draft proposal for the 2006 redefinition of the term, the IAU proposed that a planet be defined as a body that orbits the Sun that is large enough for gravitational forces to render the object (nearly) spherical. Under this proposal, Charon would have been classified as a planet, because the draft explicitly defined a planetary satellite as one in which the barycenter lies within the major body. In the final definition, Pluto was reclassified as a dwarf planet, but the formal definition of a planetary satellite was not decided upon. Charon is not in the list of dwarf planets currently recognized by the IAU.[37] Had the draft proposal been accepted, even the Moon would be classified as a planet in billions of years when the tidal acceleration that is gradually moving the Moon away from Earth takes it far enough away that the center of mass of the system no longer lies within Earth.[38]
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If it were me I'd add "... a planet be defined as a body that orbits
just the Sun
and no other object within the solar system ..." so the moon and Charon remain moons as long as they keep circling around their main planet, never mind the position of their combined center of gravity.
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