A Swedish treasure hunter found a strange formation on the floor of the Baltic Sea, speculating it could be an underwater “Stonehenge,” while others say it could be a UFO. In fact, ocean exploration experts tell PM, the sonar image in question may not be trustworthy, and the explanation for the formation (if it's real) is probably rather ordinary.
UPDATE: This week Huffington Post and other outlets are publishing reports of a "strange circular object" beneath the Baltic Sea, which some are claiming to be a UFO. The same team of explorers released a similar image last summer; here's PM's original story from August 2011 about why any UFO claims don't stand up.
Swedish treasure hunter Peter Lindberg made headlines around the world after releasing sonar pictures of a strange disk-shaped formation on the bottom of the Baltic Sea last week, saying the shape could be an underwater "Stonehenge" Media sources then speculated that it could be a sunken flying saucer, interpreting long groove-like marks next to it as evidence of a crash-landing. But Hanumant Singh, a researcher with the Woods Hole Oceanographic Institute, says regardless of what the picture looks like, these sonar images cannot be trusted.
The problem, he says, is that the pictures of this roughly 190-foot-wide disk-shaped formation were taken using side-scan sonar, a relatively inexpensive type of sonar technique useful for finding sunken ships. However, the images themselves reveal several distortions that render them virtually useless for identifying an undersea formation, Singh says.
First, he says, if you look carefully, you can see a reflection of the circular formation on the right side of the image. Since side-scan sonar is taken with two instruments that bounce acoustic waves in opposite directions from the boat, a feature on one side shouldn’t affect the image on the other side. “This means you’ve got ‘cross-talk,’ in which one channel is electrically contaminating the other,” Singh says. In other words, the sonar instruments aren’t wired properly. Strike one, he says.
Strike two: The black horizontal lines going through the image show that sonar signals are dropping out (that is, the instruments aren’t detecting them), further calling the measurements into question, Singh says. Finally, he says, the edges of the image, just beyond the circular formation, are gray, meaning the sonar couldn’t tell what was there. That shows the sonar isn’t calibrated well enough to trust, Singh says. “That’s strike three.”
Charles Paull, senior scientist at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., says that even if the formation were real, it could be something as mundane as a circular rock outcropping or the result of fluid or gas venting. Such venting causes inexplicable and poorly understood structures like pockmarks—circular depressions that Paull has seen all around the world. In one area off California alone, he says, he has mapped more than 1400 such pockmarks.
Another possible explanation that’s not quite as exciting as a UFO: The disk-shaped formation and the tracks, seen in just 300 feet of water, could have been caused by a fishing trawl. For example, Paull says, the jaws or opening of a trawl could easily have struck the bottom elsewhere and dropped a disk-like mound of sediment—or a trail of pebbles that make up the “track marks,” he says. Or, Singh says, the image could be simply fish. “I’ve been fooled hundreds of times [when using side-scan sonar] into thinking I’ve found something, when it’s just a rock outcrop or a school of fish.”
Singh has used side-scan sonar to look for shipwrecks himself, and the key, he says, is to turn the ship around and double-check anything that looks as interesting as Lindberg’s image (which the treasure-hunters apparently did not). The 2D images that side-scan sonar creates can reveal sunken ships or even underwater mines, but it doesn’t give you a 3D image, nor does it directly measure water depth. Substances that reflect light differently than their surroundings can also fool side-scan sonar. “It’s really difficult. Side-scan sonar is an art form,” Singh says.
And, Paull says, in the absence of a clear picture, people see what they want to. “The finding is curious and fun, but much ado about nothing.”