Because there are only 8 planets which are very close to the sun as compared to others and revolve around the sun.
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thank u 
please press the thanks button and mark as brainliest answer.
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The Brainliest Answer!
So it begins again: the neverending debate about who gets to be a planet and who doesn’t. Everyone can bring their own interpretation of the science to the table — and everyone has their own preferred naming scheme — but when I think about the Solar System, I try to think about it in the context of all star systems.Believe it or not, as far as we’re able to tell, they all have some very important things in common.
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