“The Probe” (S2E17) was the last episode of the original Outer Limits (1963-1965)

Four survivors of a plane crash in the Pacific Ocean find themselves inside an alien craft. They soon learn it’s a space probe testing Earth’s environment.

Unfortunately, a giant microbe had contaminated the probe during a prior landing and it kills one of the crash survivors. Eventually the others figure out how to communicate with the aliens and they are freed. As the human are rescued, the probe takes off and destroys itself so as to not contaminate other planets.

A decent episode, although the characters jump to some incredible conclusions regarding their predicament. Although the miniature used for the exploding craft at the end was pretty lame.

The giant microbe was later reused as the Horta, on Star Trek TOE S1/E25.