I saw this story the other day at Space.com about the search for a long-lost planet, Theia, that astronomers think may have existed in our solar system. Of course, my first thought is: Theia?! What kind of lost mystery planet name is that? It needs a cool mystery moniker like PLANET X, OBJECT ZERO, ROGUE or NOMAD. But Theia? Too girly for a planet -- heck, I dated a Theia back in the day, and I suppose you can say she had "a heavenly body" (she actually did some modeling), but it's hardly a name befitting an enormous spinning rock hurtling through space around a burning ball of nuclear reactions. Okay, I know it's the name of a Greek goddess, one of the Titans, but still! My issues aside, I still love a good mystery and the theory on this one basically goes that a sibling of Earth, Theia was a satellite about the size of Mars, and it collided with Earth about 4.5 billion years ago. After the impact, some of the debris may have clumped together to form our Moon, while the rest just drifted off into space. Currently, NASA is using a pair of STEREO probes (launched in 2006) to search for traces of Theia, which is near impossible to do using land-based telescopes. The STEREO probes are entering spots in space called Lagrangian points, which are equilibrium points between the Sun and Earth's gravitional fields and where space flotsam tends to gather (a space gravitational storm drain of sorts). It is hoped that while in these areas, the probes will be able to find some left-over chunks of Theia in the form of asteroids. Despite the amount of time and energy that has been devoted over the decades to the study of the stars and space, it's mindboggling the amount of stuff we don't know. Dark matter, black holes, quasars, Hanny's Voorwerp . . . who knows what else existed out there, or even in here? As I mentioned recently when discussing Predator X (see, now that's a cool name for an unknown mystery creature!), we only know about the things that we can find remnants of -- who knows how much stuff there was, terrestrial or extraterrestrial, that either no traces remain or we haven't discovered yet? So many mysteries out there!