Anomaly on the sonar
In June 2011, a Swedish treasure-hunting group called the Ocean X Team was surveying the floor of the Gulf of Bothnia for shipwrecks. During a final pass with their side-scan sonar, an unusual image appeared. At a depth of about 90 meters (300 feet), they detected a perfectly circular object. The feature is 60 meters (200 feet) in diameter and rises 3 to 4 meters (10 to 13 feet) above the flat seabed.
The sonar imagery also revealed what appeared to be a 300-meter-long (985-foot) track leading directly to the object, suggesting something had skidded to a halt on the seafloor. The discoverers, Peter Lindberg and Dennis Åsberg, noted other strange features, including what they described as stair-like formations and straight edges, which seemed unnatural. The initial sonar image was blurry, but its distinct circular shape, often compared to the Millennium Falcon spacecraft from Star Wars, quickly attracted media attention. A second, smaller circular object was also detected on sonar about 200 meters away.
Glacial erratic or something else?
A follow-up expedition in 2012 aimed to gather more data. Divers who visited the site described a rough, rounded surface. The Ocean X Team also reported that their electrical equipment, including cameras and a satellite phone, repeatedly failed when their vessel was within 200 meters of the object, only to start working again once they moved away. This claim of electromagnetic interference has not been independently verified and is a subject of much debate.
Samples of rock recovered from the anomaly were given to Volker Brüchert, a geologist at Stockholm University, for analysis. His examination concluded the samples were mostly common rocks such as granites, gneisses, and sandstones. One sample was identified as basalt, a type of volcanic rock, which is not native to that specific location on the seafloor.
The prevailing scientific explanation is that the anomaly is a natural geological formation. Specifically, it is likely a glacial erratic—a large boulder transported and deposited by glaciers during the last Ice Age. The entire northern Baltic region was shaped by glacial processes, which could account for both the object's presence and the rocks' composition. Geologists argue that the "runway" is likely a drumlin, an elongated hill of glacial debris. The low-resolution sonar used in the initial discovery may have also produced distortions that made the natural formation appear more artificial than it is.