Some say aliens are responsible for this 200-foot-diameter finding shaped like the Millennium Falcon from Star Wars, found in 2011 on the bottom of the Baltic Sea.

Others believe it could be a sunken ship or anti-submarine device from World War II, now resting at a depth of almost 300 feet.

Peter Lindberg, head of the Swedish underwater exploration group Ocean X Team, which located the object using side-scan sonar, credits Mother Nature.

“It is probably made by a biochemical process, as objects like this are common in the Baltic Sea — only they’re never anywhere close to this big,” says Lindberg.

Read More: 6 Places You Didn't Know You Could Scuba Dive

But it’s not the size of this object, composed of magnesium, iron and titanium, that baffles Lindberg most, but its inexplicable communications.

“We turned off all instruments, and everyone on board turned off their cellphones. Then we found a signal, 40 megahertz strong, coming from nearby. But the nearest land — a lighthouse — where you might find such a signal is 20 nautical miles away. And our equipment can only measure 2, maybe 3, kilometers (about 1.5 miles) away.”

Related Reading: 7 Facts You Didn't Know About the Sea Cucumber

Which leads Lindberg to believe the signal is originating from the anomaly. “But we can’t say for certain whether it’s trying to receive or broadcast that signal.”

Further complicating this finding is the fact that the first anomaly isn’t alone. A second, shaped like a monolith — 90 feet long and 21 feet wide — has also been located. So has a series of three peaks.

“The highest is 40 feet high, and they stand in a row, with 60 feet between them," says Lindberg. "They’re like nothing you find in the Baltic because of the Ice Age.”

What does it all add up to? He can’t say.

“Perhaps it’s just nature playing tricks on us. But it does need to be explored further and measured again, and I would like to do it before I put my gloves on the shelf a final time.”