Asked by bubulis to Aggelos, Andrew, Eileen, Naomi, Shane on 14 Nov 2012.
Keywords: dwarf planet, solar system
A dwarf planet is something big enough that its own gravity can control its own shape, but not big enough to control the objects around it. Pluto is a dwarf planet and there are another four that we know about (called Ceres, Makemake, Haumea and Eris), but I don’t think we can claim to know how many there are yet.
Five of them! For a long time, scientists argued about whether or not Pluto was a planet, or a dwarf planet (scientists like to argue with each other sometimes!). Eventually the decided it should be classifed as a dwarf planet, and so it joined the other four.
I think the space guys keep changing their mind on what exactly is a dwarf planet, or a proper planet or just a rock floating around in space. Trying to classify things into one type of thing or another is of these annoying things that humans do all the time. We do it with species too, and really it all comes down to exact definitions that get changed all the time. It annoys me when something i did know the answer to once gets changed because someone woke up one day and altered the rules as to whats in and whats out!
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