Ice Rings

What’s 2.5 miles wide, perfectly circular, and warm enough to melt ice?
I don’t know either, but there are at least two of them in Russia’s Lake Baikal.
They were spotted in April from the international space station.

What’s 2.5 miles wide, perfectly circular, and warm enough to melt ice?
I don’t know either, but there are at least two of them in Russia’s Lake Baikal.
They were spotted in April from the international space station.