This strange almost perfect 'ice circle' has appeared on a frozen lake in Siberia.
While scientists have ruled out UFO involvement, they are puzzled as to how the mysterious, 2.5mile-wide geological phenomenon has formed in Lake Baikal.
It was spotted at the southern edge of the lake while another was seen near the centre. The images were taken by astronauts aboard the International Space Station circling 220 miles above Earth.
They charted the progress of the circles when they first appeared on April 5 until April 27 when the ice was beginning to split apart.
'Throughout April the circles are persistent,' a Nasa spokesman said.
'They appear when ice cover forms, and then disappear as ice melts. The pattern and appearance suggest that the ice is quite thin.'
Ice cover changes rapidly at this time of year on the Russian lake and can melt and freeze overnight. Scientists believe a spurt of warm water rose to the surface creating the distinctive pattern but are puzzled by the source of heat.
via Mysterious 'ice circles' in remote Siberian lake baffle scientists | Mail Online.
Meteor? Volcano? Hidden UFO?