Which Richard Matheson story was adapted as the episode 'Third from the Sun'?

The Richard Matheson story adapted as the episode “Third from the Sun” is “Third from the Sun.”

The Twilight Zone episode aired on January 8, 1960, as the fourteenth episode of the original series. Its teleplay was written by Rod Serling and directed by Richard L. Bare, while the story credit belongs to Matheson.

Matheson’s short story first appeared in the October 1950 issue of Galaxy Science Fiction. Both versions follow people escaping a planet threatened by nuclear war, but the television adaptation builds toward a famous reversal: the supposedly alien destination is revealed to be Earth, the third planet from the Sun.

The answer is sometimes confused with “Steel” or “Button, Button,” which were also Matheson works adapted for Twilight Zone productions. Those are separate stories; “Third from the Sun” is both the story title and the episode title.