The Presidential X-Files: How Jimmy Carter filed a UFO-sighting report in 1973

In October 1969, a young Georgia politician was leaving a fundraiser when he spotted a large object glowing in the sky.

Four years later, in September 1973, he formally filed a UFO sighting report with the National Investigations Committee on Aerial Phenomena (NICAP).

That politician was Jimmy Carter, who went on to become the United States' 39th president.

A new episode of NASA's Unexplained Files, which airs Tuesday at 9 p.m. on the Science Channel, explores Carter's UFO filing.

Author William J. Birnes said in the episode: "When he looks up in the sky and he sees an object, it is bigger than the moon. He says to himself, 'That is the darndest thing I ever saw.'"

There is no reasonable explanation for what Carter saw that October night, but it continued to occupy his mind.

See photos of Jimmy Carter's hometown in Plains, GA:

During Carter's 1976 presidential campaign, he brought up his UFO encounter. He promised that if he was elected, he would encourage the government to release "every piece of information" about UFOs to the public.

While Carter did win the election, he later backed away from his promise, saying that the release of such documents would cause national security "defense implications."

In a 2007 interview with CNN, Carter was asked about his UFO sighting, to which he replied: "It was unidentified as far as we were concerned, but I think it's impossible in my opinion — some people disagree — to have space people from other planets or other stars to come to us. I don't think that's possible."

Tune in to NASA's Unexplained Files Tuesday at 9 p.m. on the Science Channel.

See photos of Jimmy Carter through the years: