With James Arness, Kenneth Tobey and Margaret Sheridan.

A low-budget loose adaptation of John Campbell's "Who Goes There?", and redone again in the 90s by John Carpenter. The 1951 version is one of the better 50s Sci-Fi films (there are are only 2 others in the running: "Forbidden Planet" and "War of the Worlds"); not just because it's scary as hell, but because the script, photography and dialogue are first-rate. It's worth seeing even if you're not a sci-fi fan.

The scene I'm reminded of is early in the film, when the explorers locate the wreck of a flying saucer barely visible under the arctic ice. In an attempt to determine it's shape, they surround the object and spread out until they mark off the perimeter of the object--a huge circle. The scene is beautifully filmed and really sends a chill down your spine (no pun intended). From then on it's a real thrilla and it never lets up.

http://en.wikipedia.org/wiki/The_Thing_from_Another_World