It is the winter solstice. T<span>he solstice that marks the onset of winter, at the time of the shortest day, about December 22 in the northern hemisphere and June 21 in the southern hemisphere. I know this mainly because I had the same question. Good luck :)</span>
The name for such a hole is "caldera" which is a word of Spanish origin meaning "a pot" or a "cooking pot" (thing of cauldron!) - and this word is used because it resembles the shape of this hole.
Often the Calderas are filled with water forming lakes and often there is an island in the middle of the water.
Saturn has 62 moons. Hope this helps! Have a wonderful day!