During the first season of The Outer Limits, this episode titled "The Mutant" aired on March 16, 1964. Most notable to myself is the portrayal of the mutated space researcher Reese Fowler by none other than a favorite actor of mine - Warren Oates.
By way of an introduction to this episode, here's the opening narration:
"At this very moment, our horizon is menaced by two explosive forces, both man-made. One is a deadly wonder; the other, wondrously alive. Both forces have compelled Man to reach out for worlds beyond his own, new worlds where he may find peace, and room to grow. This is the first of those new worlds. The United Nations of Earth have claimed it, and called it Annex One. It is almost identical to Earth, except that there is no night--sunlight is constant. Early reports from the small expeditionary team stationed on Annex One indicated that the ancient planet appeared suitable for colonization by Earth's overflowing population. But the most recent reports have contained unspoken, oddly disturbing undercurrents, and the United Space Agency has decided to investigate. The man chosen: Dr. Evan Marshall, psychiatrist."