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" on how he designed 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 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 behavior if not in appearance. Mesklin is sometimes viewed as the main character of Mission of Gravity.

Description

Mesklin is a fictional planet orbiting one of the stars in the 61 Cygni binary star system.[2][3] Its mass is sixteen times that of Jupiter, or 4,800 times Earth mass.[4][5]: 215  It has a very high rate of rotation, one day on the planet lasting only eighteen minutes.[2] As a result, the planet is significantly flattened with a large equatorial bulge: the diameter at the equator is 77,000 km while the diameter between the poles is slightly below 32,000 km. By comparison, the diameter of Earth is approximately 13,000 km.[2][3][4] The planet thus has a significantly higher mass than Jupiter within a much smaller volume, and its core is made up of collapsed matter.[4][6] The surface gravity is very high at 665 times Earth gravity at the poles, but at the equator the effective gravity is only three times Earth's as the rapid rotation produces a significant centrifugal force that counteracts most of the gravitational force.[7]

Artist's rendering of Mesklin

Mesklin orbits its star in an elongated ellipse, completing a full revolution in 1,800 Earth-days.[7][8]: 1424–1425  The high orbital eccentricity combines with a pronounced axial tilt to result in an uneven seasonal cycle. In the southern hemisphere, the springs and summers are very lengthy (at 28 Earth-months each) and the autumns and winters much briefer (2 months each); the pattern is reversed in the northern hemisphere. The two hemispheres thus have significantly different climates.[8]: 1425 [9]: 87  The planet is cold, with average temperatures ranging from −50 °C at the closest approach to its star to −180 °C at the furthest point in its orbit.[7][10][11]: 73  Mesklin is itself orbited by two small moons and has a large ring system.[3][5]: 215 

The surface is covered mostly by methane (CH4) and ammonia (NH3), both mainly in the liquid state; the oceans are primarily made up of methane, while the ammonia is also present as snow.[2][3] The atmosphere is principally composed of hydrogen, and its density decreases with increasing altitude to such a degree that atmospheric refraction through the successive layers produces the optical illusion that an observer on the surface perceives the ground as curving upwards, as if living on the concave inside of a bowl rather than the convex surface of a spheroid.[3][12]

The planet is inhabited by various lifeforms.[2][9]: 89  The intelligent native inhabitants, the Mesklinites, resemble centipedes or caterpillars.[2][3][8]: 1424  They are 40 cm long and 5 cm wide, with eighteen pairs of legs ending in suckers as well as a forward pair of pincers for manipulation and a rear pair for attaching to the ground.[3][5]: 218 [13] They have four eyes and mandibles.[3][13] They have a tough exoskeleton that allows them to withstand the planet's strong gravity.[9]: 88  They have no lungs but breathe hydrogen by absorbing it directly from the atmosphere in a manner similar to that used by the respiratory system of insects, whereas oxygen is toxic to them.[3][5]: 216, 218 [14]: 107–108  They are able to survive while submerged for extended periods of time by breathing dissolved gases.[14]: 107–108  Their lifespan is much longer than that of humans.[9]: 89  They have a strong fear of heights and of being underneath objects, owing to the danger posed by such things in a high-gravity environment.[2][8]: 1425 [9]: 88–89 [14]: 108  For similar reasons, they have no concept of flying or throwing things.[8]: 1425  Their society is pre-industrial with rudimentary technology including seafaring vessels.[2][3][8]: 1424