Can moons have moons?

Planets orbit stars. Moons orbit planets. But no moons have their own moons (let’s call them submoons). Why is that?

Is Pluto a mega-comet?

Short answer: Well sort of, but it’s more useful to think of it as being built from the same stuff as comets. Like an Uncle of the comets. Read on for an explanation. Earlier this week my wife mentioned a headline she saw.  “Pluto is a giant comet?  Whoa!” It was all over the place:…