Pictures of frightened gasps and wide eyes as a giant gray disc hovers over the city usually make the front page of a grocery store tabloid.

With recent reports from Yahoo News and CNN, unidentified flying objects, or UFOs, once more have caught the attention of government officials. In November, the National Press Club had a news conference in Washington D.C., led by former Arizona Governor Fife Symington, members of the Air Force and government members from seven different countries.

According to a Nov. 1 news release, the leaders of the conference once more aimed to persuade the government to take an interest in the latest accounts from on-duty Air Force pilots and to reopen investigation, paying special attention to cases relating to national security. The outcome of the conference has not produced searchable results and ultimately might result in a continuation of ongoing curiosity and enthusiast debate.

Will this ever lead to a confirmation that those green visitors in the night are real? Weird Science Professor Taner Edis said it will not.

"There is no credible physical evidence for any UFO landing, UFO abduction, you name it," Edis said. "It seems to happen without leaving any credible trace."

Yet, over the past century, various organizations and people sitting waist-deep in the fad have tried to prove - and fake - the existence of the extraterrestrial through pictures, videos and even phone conversations. Countless Web sites, like the Mutual UFO Network, devoted to this phenomena post blogs concerning the latest sightings and scientific breakthroughs. Even Facebook has groups whose members continuously report sightings on discussion boards.

Edis said many of these cases owe themselves to natural occurrences in space or to aircraft. He said unexplained cases have drawn people's attention since the 1940s. Documented sightings from both Air Force radar and the public caught the attention of speculators and government officials.

"There was some people in the military saying that there was legitimate reason to be concerned over here because what if what we're seeing ... [was] actually evidence of Russian spycraft, or the Soviets [had] developed some kind of new technology," Edis said. "Mostly, they looked at it and decided it was essentially noise."

Edis said the military neglected its investigations and sent out reports to the public that failed to give enough explanation as to what had been seen.

This caused people to further blow their claims of sightings out of proportion because they feared that the government was keeping the truth a secret. He said that with the addition of the UFO pop culture that had been blooming in comic books and science fiction since the 1930s, the "UFO movement" spread.

In recent years, sightings have decreased and abduction claims have taken their place, Edis said. He said these claims generate from pop culture and should not be considered as a phenomenon to explore scientifically.

"The fact that there's this kind of residue of unexplained cases is not any more significant than the fact that there's always a certain percentage of murders unsolved," Edis said. "We don't assume that because there are murders unsolved that there are aliens coming down and slitting people's throats."

Mark Rodeghier, scientific director at the Center for UFO Studies in Chicago, seems to think otherwise.

The Center for UFO Studies, started in 1973 by Ohio State University astronomy professor Dr. J. Allen Hynek, collects information from phone calls or e-mails written by people claiming to have experienced some type of UFO encounter. The center hopes to solve the unexplained cases by making the media and scientific community more aware of the ongoing UFO problem.

"If there's strange things flying around in the sky, why should we be ignoring them?" Rodeghier said. "Tax dollars are wasted because there's an incredible bias against UFOs being something worthy of study."

Rodeghier said their team of academics, librarians and other volunteers does not investigate every case, especially if it's an incident that gives no further assistance to their research.

"But of the ones remaining - certainly a fraction of these - I would say there's some other intelligence here, floating around in our skies," Rodeghier said. "I've obviously, for years, thought about alternative explanations, and I can't find any that are as viable."

Kirksville Regional Airport has handled a handful of calls about local sightings in the past years that are always investigated and have easy, natural explanations, airport operator Rusty Milburn said. Sergeant Brent Bernhardt of the State Highway Patrol said he and his colleagues also have to take their UFO sighting calls seriously.

"We've had people report suspicious sightings," he said. "In the 17 years I've been in the highway patrol ... there are two such incidents that I personally have knowledge about. One of them was an aircraft, and the other was a meteor shower."

Meanwhile, UFO supporters and researchers have to come up with their own explanations for the strange shapes in the skies. Rodigheir said he believes that recent scientific developments could point to reasons for assumed spacecraft.

"Physicists today talk about extra dimensions in space," he said. "We could be visited, not by aliens 50 light years away, but by aliens from other universes even. That's what I think could be happening. It would be nice to know."