"A circle in thin ice in Lake Baikal, Russia" photographed from space on 23 April 2009 by an International Space Station astronaut. "Throughout April, the circles are persistent -- they appear when ice cover forms, and then disappear as ice melts." The "origin of the circles is unknown." [4256x2913]

https://go.nasa.gov/34CHF1E via /r/spaceporn http://bit.ly/32uqpdJ