What is a dwarf planet in space?

Answer 1

A dwarf planet is a name given to a minor planet not considered to qualify as a true planet, mostly due to its smaller size. For example, in 2006 the IAU re-classified Pluto as a minor or dwarf planet, thereby demoting it from consideration as a true planet. Largely the decision could be attributed to the discovery, sometimes by space-based telescopes with higher resolving power, of many other objects like Pluto ("Plutinos") beyond its orbit which also orbit the sun but whose merits for the status as planets could be questioned; this raised the issue of what do we consider to be a true planet? The new criteria which excluded Pluto was whether it had cleared a significant fraction of debris from its orbit - which Pluto has not done. The other criteria that Pluto still meets is that it is in hydrostatic equilibrium (basically, a nice spheroidal shape) and is in solar orbit (it cannot be a moon, to be a planet). Examples of other dwarf planets would include Eris, Ceres, Sedna.