'Hey Bill Nye, What If the Moon Were Made of Green Cheese?' #tuesdayswithbill | Big Think.

Hi. Dan Greene here. Bill, I wanted to ask you a hypothetical: if the moon was really made out of green cheese, how much mass would it have? What would its gravity be like? How would it affect our tides differently than the real moon does? And just for fun, how much milk would it take to make that much green cheese? Thanks for your answer. Dan.

Great question about the moon being made of cheese, specifically as I understand it, green cheese. If it were green cheese, like really green, I would expect it to reflect a little more green light than it does. I mean, it would depend; does it have a rind? Does it have that wax that they put on at the cheese shops? I'm not sure.

Anyway, I can tell you from experience that in general, cheese floats. In general, with floating cheese, you got to figure its specific gravity, that is to say how much mass it has for how much volume it takes up, is somewhat less than rocks. If water is one, rocks are one and a half; they're two, they're twice as dense as water. They're not 50 times as dense, just twice as dense. Rocks sink, but they don't sink like a bullet.

So a moon that was 80 percent the mass of the current moon would have 80 percent of the effect on the tides. But if it were 80 percent of the mass, its orbital distance would probably be different. Would it be set up to librate in the same way? That is to say, the moon currently keeps the same face to us with every orbit. That's because it spins almost exactly one time as it goes around the Earth. It has a little wobble to it, where you actually see somewhat more than just half of the moon if you're really diligent with a telescope, paying close attention.

And then the other thing I would wonder about a cheese moon, you know, rocks are pretty solid, but cheese often is not. I wonder if it wouldn't have modes or vibrational oscillations within its own shape that are noticeable. I wonder if its spin wouldn't—spinning once with each orbit—I wonder if it wouldn't have an equatorial bulge. I wonder what would happen to it with other cheesy objects with it, you know, meteorites of cheese, cheeseteorites, whatever they're called.

And I wonder if it wouldn't outgas or evaporate in the blackness of space. Also, cheese freezes. So on the far side of the moon, or the near side depending on the time of month, you might have some lunar freezing, which then could potentially affect the shape because it would affect its gravity with one side solid, changing density relative to the other side. The geode, as it's called, the shape would change with its own gravity.

So, there would be some issues. You'd notice it right away. And I think another issue to keep in mind, if the moon turns out to be made of cheese, it just really expands our possibilities for a lunar base because there would be limitless food. It does, for those of you who are gluten-free and dairy-free, you may not want to be an astronaut on a lunar mission now if it turns out that it's made of green cheese.