A mysterious cylindrical object is sitting 300 feet at the bottom of the Baltic Sea between Sweden and Finland, and nobody knows what it is -- yet.
Deep sea divers using remote-controlled cameras are heading to the site on Friday. They'll try to determine the exact identity of the object, which side-scan sonar first revealed in June 2011.
"Side-scan sonar is not a photograph and it can create false echoes, so it's not crystal clear what exactly it is that you're recording," Radford said. "The object that we're talking about is basically flush with the ocean floor, and side-scan sonar is much less reliable for things like that."
In what's been compared to an episode of "The X-Files," Peter Lindberg, captain of the Ocean Explorer, and his co-researcher Dennis Asberg made global headlines last year when they presented sonar images of a nearly 200-foot-wide circular anomaly -- looking very much like the fictitious Millennium Falcon spacecraft from the "Star Wars" movies.
"We don't know whether it is a natural phenomenon or an object," Lindberg told Fox News.
Is it a spaceship, a Russian warship or an ordinary stone formation?
This is a composite image of how three alleged UFOs maneuvered about in the sky over Melbourne, Australia, in early February, 2013. The final verdict isn't in yet on whether they're birds, aircraft, balloons, bugs or something truly unidentified.
These candle-lit Chinese lanterns can rise high into the sky and are often mistaken for UFOs.
On Dec. 20, 2012, a bright, circular object (pictured at the top of this composite image) was videotaped exploding in the skies above Sacramento, Calif. It wasn't immediately identified, resulting in speculation that it was either an alien spacecraft, military top secret weapon, runaway planet, North Korean satellite, among others. Within a short period of time, it became apparent that this was a weather balloon. The bottom part of this image shows such a balloon as it ascended over Tampa Bay, Fla., on July 2, 2012, and exploded in an identical manner as the Sacramento object, probably much to the dismay of all true ET believers out there.
This is a composite of images shot by two eyewitnesses of a boomerang-shaped UFO they reported seeing over their Burbank, Calif., home on Oct. 5, 2012. Mutual UFO Network photo/video analyst Marc Dantonio concluded the object was likely "a balloon, floating on the wind that has collapsed in half."
This four-image series of lights in the sky was recorded over Warren, Mich., on Jan. 10, 2013. The lights were seen changing into several patterns. The most logical explanation for these types of UFOs is a series of balloons or lanterns.
This composite image shows four different times that alleged UFO were photographed above Earth by either space shuttles or the International Space Station. The big question is whether or not they are truly unidentified objects or if they are more likely reflections from spacecraft windows, meteors or fast-moving spacecraft-generated debris.
What appear to be pink-red UFOs are actually lens flares from the Google Earth street view camera as it snapped images in Texas (left) and New Mexico (right).
These two flying saucer-shaped, pink-colored lens flares were created by the Google Maps camera as it drove through locations in Sedona, Ariz. (left) and Flagstaff, Ariz. (right). The images were snapped in April 2009. Submitted to HuffPost by trenna.
This skybound lens flare was created by a Google Maps camera in June 2008 over Whiteriver, Ariz. Submitted to Huffington Post by Cheryl Weeks.
This very Earthbound lens flare was created by a Google Maps camera in November 2007 at Gulfport, Miss. Submitted to Huffington Post by Jenni Parker.
This seemingly grounded lens flare was created by a Google Maps camera in January 2008 at Eureka Springs, Ark. Submitted to Huffington Post by SE.
This lens flare appears to be following a car. The Google Maps image was created in October 2008 at Escanaba, Mich. Submitted to Huffington Post by Mary Robinson.
On the night of Sept. 28, 2012, a group of strange-looking lights appeared in the sky near Cincinnati, Ohio. First there was one, then, two, then three lights, slowly descending. It turns out, however, that these lights were originating from a group of skydivers performing a pyrotechnics jump at the La Salle High School homecoming event.
Some UFO sightings may be due to a natural phenomenon known as sprites, like this one shown from 2006. "Lightning from [a] thunderstorm excites the electric field above, producing a flash of light called a sprite," said geophysicist Colin Price.
Clouds: Saucer-shaped or "lenticular" clouds that form at high altitudes have been confused with UFOs.
Blimps or advertising balloons: These can look like flying saucers from some angles, especially at night.
On June 19th the Swedish-based diving company Ocean Explorer discovered something they've never quite seen before. They were exploring in the Baltic Sea between Sweden and Finland looking for sunken treasures when a very unusual image suddenly appeared on the sonar. A 197 feet diameter cylinder shaped object was discovered at the depth of approximately 275 feet which resembles the Millennium Falcon from the movie Star Wars.
An image released on June 15, 2012, shows a close-up view of the unidentified object sitting on the bottom of the Baltic Sea.
Close-up of rock bed that forms the Baltic Sea UFO, which still mystifies researchers.
One of several odd stone circle formations, sitting on top of the unidentified object at the bottom of the Baltic Sea.
A circular UFO hovers above the Neumayer-Station III research facility in Antarctica on Aug. 10, 2012. Theories ranging from a simple weather balloon to a more elaborate ship from another planet have run the Internet gamut. The next slide shows a closeup of the object.
This is a closeup of the UFO from the previous slide. No official explanation has been offered about the object.
Pictured is a quad copter -- a deliberately manufactured UFO created by special effects wizard Marc Dantonio for a National Geographic special, "The Truth Behind: UFOs," which aired in December 2011. On the left is what the small device looks like resting on the ground, measuring 4 feet in circumference. At right, is how it appeared behind a tree in the night sky.
In February of 2012, this fireball was captured by a Texas police chief's A dashboard camera. F.A.A. say this was probably a meteor, falling to Earth. .
Meteors: Space debris can create a spectacular light show when it burns through the Earth's atmosphere, and sometimes reported as UFOs.
Civilian or military aircraft: Planes can look mysterious at night or in certain light conditions, thus confusing an observer.
The researchers will spend between six and 10 days at the site, using sonar to create 3D images of the bottom of the specified part of the Baltic Sea.
Explanations for the odd anomaly include a meteor, a naturally-occurring gas well and the possible remains of a 19th-century Russian warship.
Of course, let's not forget about all of those hopeful souls who would love this to turn out to be a crash-submerged spacecraft from another world.
"If this were a UFO, that would indeed be a strange thing," Asberg told Fox News. "I'm just not sure, but we'll see soon."
Radford, who is also the author of "Scientific Paranormal Investigation: How To Solve Unexplained Mysteries," said he thinks the mystery will only continue if the divers don't find anything.
"Because then they'll say, 'Whoa, hold on here. We have this image that was taken in 2011. How come they're going back there and not finding it there?'" Radford said. "And there will be conspiracies about that."
Watch this video about the discovery of the Baltic Sea anomaly: