Mesklin

Mesklin is a fictional planet created by Hal Clement and used in a number of his hard science fiction stories, starting with Mission of Gravity (1954). Alongside the novel's original 1953 serialization in Astounding Science Fiction, Clement published an essay titled "Whirligig World" detailing the process of designing the planet to have the properties he wanted. The idea came from an object that was at the time believed to exist in the 61 Cygni system, and which might represent an extrasolar planet.

The planet Mesklin is distinctive for the interaction of its strong gravity with the centrifugal force due to its fast rotation, giving it a gradient in the perceived force of gravity from 3 g on the equator to 665 g on the planet's poles. It is inhabited by native lifeforms, including an intelligent centipede-like species, the Mesklinites.

Mesklin is considered a prototypical example of hard science fiction worldbuilding, an exotic milieu that nevertheless accords with known facts and laws of physics. While the planet itself is vastly dissimilar to Earth, its inhabitants are commonly regarded to be noticeably humanlike in behaviour if not in appearance. Mesklin is sometimes regarded as the main character of Mission of Gravity.