An extraterrestrial lifeform will imitate other organisms

John W. Campbell Jr. : writer
A parasitic extraterrestrial lifeform will assimilate other organisms and in turn imitates them. A group of scientific researchers, isolated in Antarctica by the nearly-ended winter, discover an alien spaceship buried in the ice, where it crashed twenty million years before. They try to thaw the inside of the spacecraft with a thermite charge, but end up accidentally destroying it when the ship's magnesium hull is ignited by the charge. The Thing infiltrates an Antarctic research station, taking the appearance of the researchers that it absorbs, and paranoia occurs within the group.

Novel "Who Goes There?"