In some ways the main character of Hal Clement's under-appreciated novel, Mission of Gravity, is not Charles Lackland, the human explorer dispatched to the planet Mesklin to retrieve stranded scientific equipment. Nor is it the small caterpillar-like creature named Barlennan, a native of Mesklin who agrees to help Lackland find and recover the equipment. Rather, the main character is the planet Mesklin itself, a place with utterly unique characteristics that make themselves felt during every interaction and calculation the intrepid Lackland and his guide have to make. Odd, formidable and of serious interest to the human scientists sent to study it, Mesklin has, at its poles, the strongest gravitational pull in the known galaxy. A place of obvious interest to Earth's scientists with the potential to provide human beings with the most new insights into the space-time continuum since Einstein's day, Mesklin proves a daunting challenge to the explorers who have to cope with the strange and often trying conditions.
Barlennan and his crew are creatures designed for life under heavy gravitational conditions. The journey to the pole with Lackland, though, first takes them out of their native habitat and across Mesklin's equator, a region of the ovular planet where the lack of gravity threatens the tiny creatures with getting carried away by the wind and other hazards. Clement is careful to pursue at every turn the implications of the conditions on Mesklin, and his insistence on this gives the novel a certain sense of authenticity, belied only by the fantastic subject matter. Although the novel is, as a result, considered "hard science fiction," it remains refreshingly free of jargon or overly-complicated explanations.
While Mission of Gravity is an interesting read by virtue of its sincere interest in science, it is also a gripping adventure story filled with close encounters and hair-raising plot twists. The planet Mesklin is largely unexplored, so neither Lackland nor the native Barlennan is prepared for what they encounter. Formidable terrain, unfamiliar creatures and new civilizations confront the explorers as they make their way towards their destination. The alliance between Lackland and his guide is itself something of a puzzle as Barlennan, always the opportunist, has an agenda motivating his decision to help the earthling. What that agenda is slowly becomes clear as the novel unfolds.
Mission of Gravity is Clement's most popular and enduring work.