The planet first appeared in his series of short stories, "Mission of Gravity", in Astounding Science Fiction (April-July 1953). Other fictional works using the planet or its denizens include "Under", "Lecture Demonstration", and Star Light; the book Heavy Planet is a collection of Mesklin-related works by Clement.
Clement described the basic characteristics of Mesklin in the article "Whirligig World" in Astounding Science Fiction (June 1953). Clement presumed that an "invisible" object in the 61 Cygni system was in fact a planet, Mesklin.
Clement decided that, since its mass was 16 times that of Jupiter, Mesklin would have an extremely large spin rate to partly counter its gravity (e.g., to allow humans to visit part of Mesklin). Clement wanted the equatorial gravity to be 3G, so he determined the spin rate necessary to make this occur: each Mesklin day is 17.75 minutes long (the planet rotates approximately 20 degrees a minute). As a result of this extremely large rate of spin, Mesklin is not even slightly spherical; it has a large equatorial bulge. Mesklin's equatorial diameter is 48,000 miles, while from pole-to-pole along its axis of rotation it is 19,740 miles. Clement then attempted to calculate the polar gravity, but this was suprisingly difficult. He admits, "To be perfectly frank, I don't know the exact value of the polar gravity; the planet is so oblate that the usual rule of spheres... would not even be a good approximation..." "Whirligig World" reports his initial calculations of the pole gravity to be 655G, the paper jacket of Heavy Planet reports the pole gravity as 700G, and a later program created by Clement computed it as 275G.
Clement also gave Mesklin a set of rings and massive moons. The inner moon is 90,000 miles from the planet's center, with a period of 2 hours 8 minutes.
He determined Mesklin's orbit around its sun (which Clement decided would be 61 Cygni A) took 1800 Earth-days, and is highly elliptical; at its closest point the average temperature would be -50C, while at the furthest its average temperature would be -180C. Since the orbit is eccentric it moves rapidly past its sun at the closest point, so its temperature would be around -170C most of the time.
Clement decided that this imaginary world would have native life-forms, that they would be based on methane (CH4), and that there would be oceans of methane. Unfortunately, methane has a low boiling point, suggesting that Mesklin's sun might boil its oceans and cause the methane to escape the planet entirely. Thus, Clement arranged the planet so that its northern hemisphere's midsummer occurs when it is nearest its sun. Thus, the northern hemisphere would develop a large frozen methane cap during most of its year; the southern hemisphere (where most creatures live) is protected from the sun's closest approach by the rest of the planet. He also asserted that the planet would have a fairly rapid precession.
In "Whirligig World", Clement stated that he gave "official permission to anyone who so desires to lay scenes there [in Mesklin]. I ask only that he maintain reasonable scientific standards, and that's certainly an elastic requirement in the field of science fiction."
Mesklin, "Whirligig World", and the Clement stories based on them are important in science fiction because they illustrated how to carefully incorporate all known (at the time) scientific facts into an interesting setting, which could then be used as a basis to create interesting stories.
See also Hard science fiction.