Should sun, moon, and earth be capitalized?

When Merriam-Webster indicates that a term is “capitalized” or “usually capitalized,” the MLA capitalizes the term in its publications. When Merriam-Webster indicates that a term is “often capitalized,” our practice varies. We usually lowercase sun, moon, and earth, but, following The Chicago Manual of Style, when the does not precede the name of the planet, . . .