What Hath me? by Henry Kuttner

Stuart let out his breath in a long sigh. He had no illusions about the vanishment of the Aesir; he knew he had not conquered those mighty beings. It would take more than human powers to do that. But at least he had a respite. All but the most stolid spacemen develop hypertension, and there seems to be a curious mathematical rule about that; it increases according to the distance from the Sun. Which may be explained by the fact that environmental differences also increase as the outer planets are reached -- and alien environments breed alien creatures. A great many men have gone insane on Pluto.

This was not Pluto; it was nearer Sunward than Jupiter, but the utter alienage that brooded over Asgard was almost palpable. Even the solidity under Stuart's feet, the very stones of the planetoid, were artificially created, by a science a million years beyond that of his own time. And the Aesir --