Hal Clement's best known novel Mission of Gravity is the story of an expedition across the planet Mesklin to recover a stranded $2 billion scientific probe. Mesklin is a massive world whose gravity varies between 3 and 700 times that of Earth - with lighter gravity at the equator and heavier at the poles - and whose atmospheric pressure is 18 times that of Earth at sea level. Mission success requires cooperation between Charles lackland, the human protagonist, and barlennan, the captain of a native Mesklinite trading ship, Barlennan. The Mesklinites are tiny centipede-like intelligent beings who breathe hydrogen and are fearful of heights.