Can anyone tell me why we don't capitalize the name of our planet?

Question:

Can anyone tell me why we don't capitalize the name of our planet?

Proper names are supposed to be capitalized -- like Steve, Kate, Mars, etc. Yet almost NO ONE ever capitalizes Earth. When you write 'How on Earth...?' you are talking about a place, like London or Rome. Shouldn't it be capitalized?

Best Answer - Chosen by Asker:

The lack of capitalization probably has to do with the fact that we're so used to our world that it feels strange to give it a proper name. We often refer to it as "the earth." A similar example is when we say "I'm headed to the apartment" and not your apartment complex's proper name.

We don't usually capitalize earth unless it is mentioned along with other celestial bodies, such as Mars. So we can say: "My favorite planet is earth. But Mars and Earth are very similar."

But, unless you're in grade school, feel free to capitalize it if it makes you happy.