There's no rallying cry like the idea that the US government is hiding evidence of aliens.
Almost 2 million people signed up on Facebook to storm Area 51 on Friday, and another 1.5 million said they were "interested" (whatever that means). Amid warnings from the US government, the college student who created the event changed it to a music festival.
About 75 people showed up to the police-enforced Area 51 boundary early Friday, and a total of about 1,500 actually traveled to the area.
"It started as a joke, but it's not a joke for us," guitarist Alon Burton told the AP. "We know people will come out. We just don't know how many."
Area 51 is a high-security Air Force base in Nevada, but its secretive nature has given rise to various conspiracy theories about extraterrestrials over the years. The belief that evidence of alien visitors has been hidden from the American public extends beyond Area 51, though: It can be traced back over 70 years, to Roswell, New Mexico.
An unidentified flying balloon
In July 1947, a mysterious aircraft made of thin metal foil crashed in a ranch northwest of Roswell, New Mexico during a thunderstorm. The US Air Force quickly collected the debris for examination. The local newspaper, the Roswell Daily Record, reported that a "flying disk" or "flying saucer" had been found at the ranch.
The Air Force said the debris was from a weather balloon. But in the early 1980s, a former nuclear physicist named Stanton Friedman stumbled across the 1947 news story. Friedman was convinced that the strange weather balloon had been an alien spacecraft, and that alien bodies had been inside.
He claimed the Air Force had covered up the whole thing — a "cosmic Watergate," in Friedman's words.
Friedman got others riled up about Roswell: People filed Freedom of Information Act requests, held conferences about the incident, and published books about the crash.
The outcry spurred New Mexico Rep. Steven Schiff to request an audit of government records on the Roswell incident from the Air Force's General Accounting Office (GAO).
The GAO released a tell-all report in September 1994. The flying object, it turned out, was a top-secret government surveillance balloon. It was part of "Project Mogul," a surveillance effort that used high-altitude balloons to listen for the reverberations of Soviet nuclear-testing blasts.
A different kind of cover-up
Project Mogul was led by geophysicist Maurice Ewing, who proposed a system of sound-detecting aircraft to monitor distant nuclear blasts, according to a 1994 report in The New York Times.
The Mogul team successfully detected a Soviet nuclear detonation before the project was cancelled in 1950. The project pioneered the use of polyethelene balloons, according to the Times, which are used today to lift scientific instruments into the upper atmosphere. The balloons proved too difficult to use for nuclear surveillance, however, since strong winds could easily push them out of range for radio communications.
For its report, the GAO interviewed Project Mogul personnel as well as a person who helped recover the debris from the Roswell crash site in 1947. Investigators also reviewed archived Air Force records, photos, and blueprints related to the project, as well as one of the actual balloons.
Despite all of this evidence about the true story of the Roswell incident, a 1997 CNN-Time poll found that 80% of Americans believed the government was hiding knowledge of alien life.
"This won't lay it to rest," Albert Trakowski, an Air Force officer who ran Project Mogul, told the Times when the GAO report came out. "The psychology is simple: People believe what they want to believe. In New Mexico, flying-saucerism has become a minor industry. There are whole museums dedicated to the presentation of outrageous fictions."
Today the Roswell still boasts a local museum and festival dedicated to the incident. Area 51, similarly, offers visitors alien-themed lodging, and there's even a legal brothel called the Alien Cathouse.