ROSWELL, N.M.-If you truly believe a UFO and its crew of bug-eyed aliens came crashing down here 60 years ago, rest assured: You're not alone. At least 35,000 people have descended on Roswell this weekend for the 2007 Amazing Roswell UFO Festival to commemorate a purported flying saucer crash on a nearby ranch in July 1947. Participants have filled hotel rooms and nearly doubled the southeastern New Mexico town's population for a few days.

The festival, which began Thursday, is a mixed bag that includes live concerts (one headlined by a band with a computer-generated 'alien' drummer), costume contests, a Main Street parade and a slew of lectures that ponder everything from body snatchers to "What Does NASA Really Know?"

The festival emerged in the 1990s to spark debate about the purported flying saucer crash, which the government says was a top-secret weather balloon. Believers in the Roswell Incident say the government is conspiring to hide the truth about the events of that day and, more broadly, the existence of extraterrestrial life.

Al Dooley, 59, of Seattle, said he wasn't sure what happened back then, but came to the festival to learn more. He was nestled into a seat at a convention center auditorium, eager to hear a talk on "UFO Files from the UK and Government Surveillance of Ufologists."

His wife Nancy sat nearby, visibly less interested. She was waiting for the festival to be over so the couple could move on to the next leg of their vacation in Sedona, Ariz.

"I didn't come for the carnival atmosphere. I came to listen to the speakers," Al Dooley said. "I wanted to hear what serious and educated discussion there is."

Although he's not certain whether an alien craft crashed here, he might have seen one himself in 1968 or 1969, he said.

Michael, who plays guitar in a rock band called Element 115 and doesn't use his last name, said he doesn't merely believe the crash happened. "I KNOW it," he said, as he handed out a business card.

Michael said he hoped Element 115 would one day be the house band for a huge theme park being debated here - featuring amusement rides, a concert hall and a 300-room hotel that looks like a flying saucer.

"I want to help them with that," he said. "I see millions and millions of dollars in this place - they just need to know how to market it right."

The city's convention center was swarming with vendors hawking trinkets and dolls, photo ops with costumed aliens, psychic readings and a kit to test whether your neighbor or boss is from outer space. Many peddled their books, DVDs or artwork of all things otherworldly.

Chase Masterson, a singer and actress, was signing autographs for fans who remembered her role as Leeta on several episodes of "Star Trek: Deep Space Nine."

"I am having a very interesting time exploring the theories that are set forth here," she said. "Some are completely outrageous but some are very intriguing."

The festival was being organized for the first time by the city of Roswell, after the local UFO museum hosted it for more than a decade.

Mayor Sam LaGrone said he was happily surprised by the turnout - and the economic boost it would give the city.

"I've never seen so many cars in town," he said.