“Now, I could ask you how many moons the Earth has,” the professor began. “Wait for someone in the room to blurt the obvious answer of ‘one,’ then smugly rebuke them. It is within my rights as your instructor to do this, but I am not a jackass, and all of you are smarter than that. You wouldn’t be at this university if you fell for such banal tricks. You’d have suspected I was playing at something the minute I asked such a question. So, I’m going to be straight with you on this one.

“It’s true that our planet only has one external moon. From my choice of adjective, you’ve already determined that I’m going to tell you that the planet has at least one internal moon, though you haven’t quite pieced together what an internal moon would be. The very word ‘moon’ implies externality to you: smooth, spherical rocks hurtling around one another, tethered together by an invisible rope.

“But gravity is far messier than that. Every single pair of masses in the universe is drawn to every other, no matter how far apart. Therefore, every fragment of the planet is drawn to every other fragment within it, as well as to every fragment of the outer moon, and vice versa. There is just as much gravitational drama happening underground as there is in the heavens. In certain creation myths, the planets themselves originated underground before being placed in the sky by the gods. This is not true, of course, but it does demonstrate a matter which modern thinking tends to ignore: the relationship between that which we can see above us, and that which we cannot see below.

“We’ve given Earth’s inner moon the name ‘Persephone.’ For those who know their mythology, this is probably an underwhelming choice, though it’s hard to think of one more appropriate. It’s nothing more than an orb of heavy, magnetically-charged gases, low enough in density to pass freely through solid earth, yet strong enough in field to maintain its spherical shape. It revolves primarily around the Earth’s core, though the planetary mass between it and the surface, as well the amount of planetary mass inside of it, have to be factored into calculating its orbit.”

One student raised her hand.

“Now, I know what you’re thinking. How can something like Persephone exist so close to us, yet not be known to modern astronomy? People ask the same kind of things about Nibiru, I suppose. Like many other celestial bodies, Persephone has an elliptical orbit, and as such, a segment of it occasionally crests above ground in summertime. Of course, it is so diffuse in nature that it can neither be seen nor felt, even from inside its surface. Despite this, were one to inhale deeply while the moon were passing through them, they’d then be able to taste or smell it. Most who experience this never actually realize what they’ve done; after all, who would ever suspect something so bizarre existing from just a strange flavor in the air? It wasn’t until our underground observatories came online that such a thing could be proven: we’re now able to detect changes in geological composition that come and go with the seasons, and record when they happen to map Persephone’s trajectory. Does that help to clarify?”

“Well,” she sighed. “Actually, I was going to ask why you thought ’Persephone’ was such an appropriate name, but I suppose the last bit answered that question, too.”

"You probably expected this one to have the Hellenoia tag from its title." "Well, actually-"

"-I was going to ask you about the possible moon supposedly discovered on the Earth's surface."

There is probably only one sun, though there's no telling how many moons are inside of it.