The Baltic Sea Anomaly: Sonar's Sunken Riddle

Ninety metres down, in the cold dark between Sweden and Finland, your sonar paints a shape no seabed should make: a near-perfect disc with a rim, a dome, and a long scar trailing behind it as if it slid to a stop. On the boat, somebody says the word Falcon before anyone says the word rock.

The scan that launched a thousand headlines

In June 2011 a Swedish treasure-hunting outfit called the Ocean X Team, led by Peter Lindberg and Dennis Asberg, was scanning the northern Baltic for shipwrecks and old cargoes when their sonar returned a circular feature roughly sixty metres across, sitting on the seabed with what looked like a two-hundred-metre drag trail behind it. The internet did the rest. The outline reminded people of the Millennium Falcon, and the "Baltic Sea Anomaly" was born as a sunken UFO, a crashed craft, or a submerged ruin.

The team returned in 2012 with divers and cameras. They described the object as having straight edges, right angles, a staircase-like feature and egg-shaped stones on top, and reported that their electronic equipment and satellite phones cut out when they got close — a detail that, true or not, gave the story its ghost.

What the rock says

The physical samples told a duller tale. Volker Bruchert, a geologist at Stockholm University who examined material the divers brought up, identified granites, gneisses and sandstones, and crucially the kind of rocks that glaciers carry and dump. The Baltic seabed was scraped and loaded by ice during the last glaciation, and when that ice retreated some twelve thousand years ago it left moraines, dropstones and debris fields exactly where the anomaly sits. To a geologist the "spaceship" is a glacial formation, and the dramatic sonar disc is partly the messy way side-scan sonar renders an irregular hump.

That explanation covers the mineralogy, the shape and the drag mark, which could be the track the object was left in by moving ice rather than a crash landing. It does not require anything to have fallen from the sky.

Why divers keep going back

Skeptics note that sonar is easy to over-read, that the Ocean X Team sells expeditions and documentaries, and that no independent scientific survey has confirmed anything unusual beyond rock. All fair. Yet the divers' specific claims — the reported equipment failures, the too-regular angles, the "corridor" leading in — are the kind of detail that a moraine does not obviously predict, and no one has gone down with a full research vessel to settle it once and for all.

So the anomaly stays in the gap between a geologist who has seen the samples and a diver who has seen the site, and neither has fully persuaded the other. It is a very expensive inkblot at the bottom of a cold sea.

Below, readers have filed their own accounts — dives, sonar oddities, things seen offshore — and voted them True, Fake or Not sure. Look at the rock and the runway both, then judge.