"A mountain planet is a theoretical planet whose geography includes extreme altitude changes. The weather conditions included in this article are largely based off that of Mercury, since Mercury is the closest thing to a mountain planet that we know about."@en . . "A mountain planet is a theoretical planet whose geography includes extreme altitude changes. The weather conditions included in this article are largely based off that of Mercury, since Mercury is the closest thing to a mountain planet that we know about."@en . "Mountain Planet"@en .