In a universe that exists in at least three dimensions and perhaps many more, our solar system remains an oddly 2-D place. At the center sits the Sun, with the eight planets spinning around it in a tidy plane, parallel to the solar equator. This is a function of the way the planets swirled into existence from the same cloud of dust and gas that gave rise to the sun itself—and is one of the things that got poor Pluto booted from the planet club altogether back in 2006. The ex-ninth planet travels in a steeply inclined orbit, rising above and diving below the solar plane—a clear indication that it's merely an escapee from the vast belt of comet-like objects that circle the solar system.
When astronomers began discovering exoplanets—worlds orbiting other stars—they expected those solar systems to follow the local model. But that's not how things turned out. Planet ...
