What if the Earth were made entirely of protons, and the Moon were made entirely of electrons?

What if you released a submarine into Jupiter's atmosphere? Would it eventually reach a point where it would float? Could it navigate?

The New Horizons spacecraft is currently flying past Pluto. For the last few days, it's been giving us our first clear look at the world, and it should be making its closest approach at the moment this article is posted. Either that, or hitting your car, I guess.