[www.space.com]

Kind of a chilly location for a fictionally desert planet. Cold forging ?

So Planetoids can have moons?

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Moon-oids?

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ztirffritz
So Planetoids can have moons?

Turns out, Pluto has quite a family of satellites although many scientists think of Pluto and Charon as a double planet system; in fact, many think of Earth and the Moon as a double system.

So, how would the definition differ between "planet & moon system" vs. "double planet system" ?



Edited 3 time(s). Last edit at 02/25/2013 05:17PM by SKYLANE.

I would suspect it depends on the center of mass / center of rotation of the system. For example, if two bodies were of identical mass, and identical size, then their center of rotation would be half way between the two (in which case you have an 'ideal' double planet system I would think).

As the size/mass difference becomes greater, and the center of rotation shifts towards the more massive body, you would approach the definition of a planet/moon system. Perhaps there's a certain range of values for the center of rotation that would define one versus the other.

There is an infinitesimal tug on Jupiter by it's moons but Earth and the Moon revolve around a point not centered on the Earth. The Moon is large enough to exert a pull on Earth-more than just tides. From Wiki:

The Moon completes its orbit around the Earth in approximately 27.5 days (a sidereal month). The Earth and Moon orbit about their barycentre (common centre of mass), which lies about 4600 km from Earth's centre (about three quarters of the Earth's radius).

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