There are plenty of reasons to believe in aliens, but this is not one of them. They can have their silly crop circles, but Mother Nature has her ice circles.

According to Wikipedia

An ice disc, ice circle, or ice pan is a natural phenomenon that occurs in slow moving water in cold climates. Ice circles are thin and circular slabs of ice that rotate slowly in the water. It is believed that they form in eddy currents.

 

How would you like to be ice fishing on one of these? It would be like a slow motion fair ride, complete with the barf.