Astronauts aboard the International Space Station noticed two mysterious dark circles in the ice of Lake Baikal in April. Though the cause is more likely aqueous than alien, some aspects of the odd blemishes defy explanation.
The two circles are the focal points for ice break-up and may be caused by upwelling of warmer water in the lake. The dark color of the circles is due to thinning of the ice, which usually hangs around into June. Upwelling wouldn’t be strange in some relatively shallow areas of the lake where hydrothermal activity has been detected, such as where the circle near the center of the lake (pictured below) is located. Circles have been seen in that area before in 1985 and 1994, though they weren’t nearly as pronounced. But the location of the circle near the southern tip of the lake (pictured above) where water is relatively deep and cold is puzzling.
The lake itself is an oddity. It is the largest by volume and the deepest (5370 feet at its deepest point), as well as one of the oldest at around 25 million years.