Featured Article Summary #220

Mesklin is a fictional planet created by Hal Clement for hard science fiction stories, beginning with Mission of Gravity in 1954. Clement also explained how he designed the planet in an essay called “Whirligig World,” which was published alongside the original 1953 serialization. He was inspired by a real astronomical idea at the time: a possible object in the 61 Cygni system that might be an extrasolar planet. Mesklin’s strong gravity and rapid rotation create an extreme change in effective gravity, ranging from about 3 g at the equator to about 665 g near the poles. The planet has native life, including an intelligent centipede-like species called the Mesklinites. Overall, Mesklin is often praised as a model of hard science fiction worldbuilding—strange and unlike Earth, yet still consistent with known physics. Mesklin is a fictional planet about 16 times Jupiter’s mass, but it spins so fast that one day lasts only 18 minutes, making it extremely flattened. Because of its rapid rotation and strong gravity, conditions vary greatly between the poles and the equator, and it follows a highly elliptical, tilted orbit that creates very different, long seasons in the north and south. It is very cold, has methane and ammonia on its surface, a hydrogen-dominated atmosphere, and its inhabitants—centipede- or caterpillar-like Mesklinites—breathe hydrogen, fear heights, live with pre-industrial technology, and are adapted to survive the planet’s extreme gravity. Mesklin first appeared in Hal Clement’s 1954 novel Mission of Gravity, which was serialized in Astounding Science Fiction in 1953. A 13-page companion article in June 1953 described the planet and how Clement created it in detail. Clement later used Mesklin again in Star Light and several short stories, which were later gathered in the 2002 collection Heavy Planet. In “Whirligig World,” he even invited other writers to use Mesklin, as long as they followed “reasonable scientific standards.” Clement based Mesklin on older astronomy ideas about a possible third body in the 61 Cygni star system, using the expected mass and size of “61 Cygni C” to build a believable world for his story—even though that original discovery is now thought to be likely wrong. Because a high-mass “super-Jupiter” would have extremely strong gravity, he made the planet rotate so fast that humans could survive, creating very different gravity between the poles and equator, and then calculated a very cold climate for the planet. To support life, Clement and Isaac Asimov worked out what chemistry could function at Mesklin’s low temperatures and chose methane as the key liquid, since it could stay liquid in those conditions. They also adjusted Mesklin’s tilt and seasons so that methane oceans would not boil away all the time, leaving one hemisphere more livable by timing the warmest period with ice-cap melting rather than constant overheating. A scholar, Gary Westfahl, credits “Whirligig World” (by Hal Clement) as an early key example of “hard” science fiction, showing how writers could use lots of real scientific information and extend it to build believable worlds. Later critics noted the main scientific issue was the story’s assumption that humans could send a ship to the planet, and Clement described hard sci-fi as a “game” where readers look for scientific mistakes and authors try to avoid them. In an interview, Clement even recalled MIT fans using computers to calculate Mesklin’s shape and finding a sharp edge—an error discovery that disappointed him but also proved his work motivated careful science.