Nearly 50 years since an alleged UFO was sighted at Roswell, New Mexico, a new CNN/Time poll released Sunday shows that 80 percent of Americans think the government is hiding knowledge of the existence of extraterrestrial life forms. While nearly three-quarters of the 1,024 adults questioned for the poll said they had never seen or known anyone who saw a UFO, 54 percent believe intelligent life exists outside Earth. Sixty-four percent of the respondents said that aliens have contacted humans, half said they've abducted humans, and 37 percent said they have contacted the U.S. government. The poll has a margin of error of plus or minus 3 percentage points. As for the Roswell incident, nearly two-thirds of the respondents to the poll said they believed that a UFO crash-landed in a field outside the New Mexico town 50 years ago next month. Most people -- 91 percent -- told the pollsters that they had never had contact with aliens or known anyone who had. A similar number -- 93 percent -- said they had never been abducted or known anyone whisked away by beings from another planet. But if they do meet someone from a galaxy far, far away, 44 percent said they expect to be treated as friends, while 26 percent think they'll be treated as enemies.