Still, the celebratory crowd, some of whom wore tin foil hats, chanted about aliens and admired the cuteness of a dog that accompanied a man wearing camouflage who had a rifle strapped to his chest.

“We walked until we got to the fence but there was a bunch of armed guards,” Austin Nelson, 21, recounted on Friday. Mr. Nelson and his friends had driven 18 hours from Alberta, Canada, to attend.

The event has revived an age-old question: Do aliens really exist?

Seth Shostak is a senior astronomer at the SETI Institute in Mountain View, Calif. (SETI is short for the Search for Extraterrestrial Intelligence.) Researchers there are searching for intelligent aliens — ones that “can at least use a radio transmitter,” Mr. Shostak said.

Mr. Shostak said his phone had been ringing all day on Friday.

“We don’t investigate reports of sightings here,” Mr. Shostak clarified at the beginning of an interview. “Although I have to tell you, also, that I get phone calls from people that are having difficulties with aliens in their personal lives, so I do deal with the idea.”

While Mr. Shostak said the evidence of alien life in the universe is, at this time, “essentially none,” he also contended that in all the space of the universe, it would be surprising if Earth alone was the home to intelligent life.

“It’s like saying, ‘Will we ever cure the common cold?’ I would say, we will,” he said.

As far as the green little guys that some imagine waddle through Area 51’s hallways, Mr. Shostak said there was almost no chance. Secrets like that, he said, would get out.

A third event in nearby Hiko also has food, drink and music and is geared toward “true believers,” Keith Wright, one of the organizers, said last week, including speakers who have researched the theories that extraterrestrial life has been kept under wraps at Area 51.