Pancake ice surrounds Chicago. (Barry Butler)

This is not the surface of another planet. It’s Chicago. We see photos of ice around Chicago every year, but not quite like this.

It’s a rare phenomenon, known as “pancake ice,” most common in super-cold oceans, such as around Antarctica and the Baltic Sea. If conditions are perfect, though, it can occur anywhere in the world — including the Great Lakes.

There’s a chilling explanation behind these ice formations. See what I did there? Let’s begin.

Two ingredients are needed for pancake ice: exceptionally cold temperatures and wind. It’s been a cold start to the year — record cold. For starters, Chicago saw its coldest New Year’s Day, with a record high of just 1 degree. The low was minus-9.

The cold stuck around after New Year’s Day, and the Chicago area had a top-10 coldest first week of January.

And Chicago had the second ingredient: a little wind to create some wave action and sloshing motion to help create the ice disks or “lily pad” formations.

The pancakes form as waves cause smooth pieces of ice to collide with one another, which rounds the edges. Continued collisions raise the edges, giving the pieces that unique appearance. Typically, the ice pancakes collide often enough that they eventually meld together to form one continuous sheet of ice.

I especially like the caption photographer Barry Butler chose for his nighttime shot of the pancake ice: “Chicago Has Landed On The Moon. Thursday in Chiberia.”

Not the moon, Barry. Just an extra cold Windy City.

Thank you to photographer Barry Butler for sharing his photos of Chicago with us.

(Barry Butler)