"There's very compelling evidence that we may not be alone, whatever that means," Luis Elizondo said.
The former Blink-182 star is getting renewed attention after revelations of the Pentagon's UFO research program.
The Defense Department investigated reports of everything from "glowing auras" to unidentified flying objects.
He says our brains just can't handle thinking about how things work from a space-based perspective.
The Topol RS-12M can be fitted with a nuclear warhead and travel up to 6,800 miles, but it was local Russians who were most shaken by Tuesday's launch.
Surveys in Western cultures estimated belief in aliens to be as high as 50 percent in 2015.
Government agency decides to label craft recorded in 2014 as an 'unexplained aerial phenomenon.'
Japan's defense minister said warplanes will be dispatched at reports of extraterrestrial life.