Does Saturn have a door?

Today we were reading one of Lucas' favorite books, Moo Cow Kaboom. On one page, there’s a picture of Moo Cow flying through space past Saturn.

Lucas: What is that? (pointing to Saturn) Is that a hat?
Me: No, it’s a planet.
Lucas: But it doesn’t have a door.
Me: You’re right. Then it must be a hat. Believe it or not, we have had this exact conversation before. I need to get to the bottom of this one.