Something happens to a news cycle when a 89-year-old physicist sits down on a podcast and says, in the same unhurried tone you’d use to describe the weather, that the U.S. government has recovered at least four distinct species of non-human life from crashed spacecraft.

The U.S. Defense Department on Friday released a second batch of previously classified files on ​alleged UFO sightings, including references to ‌people reporting unexplained green orbs, discs and fire...