Top Definition
A mass bigger than a minor object, but smaller than a star or brown dwarf that has no sun to orbit. It was ejected from it's solar system while forming by other planets' gravitational forces. Planemos may have a satellite (moon) that orbit them. Most planemos are gas giants.

The term is derived from PLANEtary Mass Object.

It has yet to achieve common usage from the scientific community.
The planemo drifted around the edge solar system, surprising many scientists.
by pyrotechnic August 23, 2009

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