The Baltic Sea anomaly

A shape on a side-scan sonar image of the Baltic seabed, reported in 2011 by Ocean X, a group of treasure hunters, and hailed in some quarters as a sunken UFO. A Stockholm geologist who examined rock samples from the site linked it to glacial processes.

Popular Mechanics reported in 2011 that experts were unconvinced by the image Peter Lindberg's Ocean X group had captured with side-scan sonar. Singh, who has searched for shipwrecks with the same kind of sonar, told the magazine that anything that striking should be checked by turning the boat around for a second pass, which the treasure hunters seem not to have done. He said the method gives a flat 2D picture, does not measure depth directly, and can be misled by materials that reflect differently from what surrounds them.

Ocean X gave stone samples from the site to Volker Brüchert, a geologist and associate professor at Stockholm University. Wikipedia reports that he found most of them to be granite, gneiss and sandstone. One loose piece of basalt, a type common at the site, did not belong on the seabed there, though such a find is not unusual. Brüchert concluded that the feature and the rocks probably formed through glacial and postglacial processes, since the whole northern Baltic was shaped by the melting of ice. In an email quoted by Live Science in 2012, he said the Ocean X team had largely overlooked the make-up of the samples it raised.

NBC News, carrying a Life's Little Mysteries piece in 2012, asked in its headline whether the find was an elaborate scam. The piece built that question on the view of Jonathon Hill of Arizona State University's Mars Space Flight Facility, who works on pictures of planet surfaces taken on NASA's Mars missions. Hill said Lindberg had either let his imagination get the better of him or had some other motive.