Why was Pluto demoted from planet to dwarf planet? 🤔
stretches itself just under the wire to qualify as a dwarf planet. A key characteristic that dwarf planets must possess is enough mass that their shape is determined by the force of their own gravity.
Second, it must be large enough that its gravity is strong enough to shape itself into a spheroid. Haumea is the only dwarf planet that pushes the boundary of what qualifies in this regard, but the other four dwarf planets are all appropriately sphere-shaped. Whether or not a body has cleared its orbit of debris doesn't provide any insight into the nature of the body, Metzger says, and this makes it a poor yardstick to measure a thing by. He also points out that until 2006, the idea that a planet had to have cleared its orbit in order to qualify as a planet was an entirely novel qualification that had never even been considered in the past when discussing what made a planet a planet.
Still, there is clearly something qualitatively different between a dwarf planet like Ceres and even the smallest planet, Mercury, even if the distinction is difficult to precisely describe. Gut feelings are no substitute for actual science, however, so the cleared-its-orbit qualifier is at least better in this regard.tell us something about dwarf planets that makes them special in this context.
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