Is our world unique? Is it the only one in existence, or are there others – perhaps many others – out there? Do other beings – maybe even intelligent ones – call these worlds their home, and live out their lives completely unbeknownst to us?
It was only in 1995 that we first discovered evidence that other stars had planets, as ours does. Now we have detected many thousands of other worlds, and evidence suggests that a majority of sun-like stars possess them. Most of these stellar systems bear little resemblance to ours. The easiest planets to detect are massive worlds located close to their stars, so "hot Jupiters" dominate the current list of exoplanets. As our surveys continue, however, we are discovering more and more Neptunes and even super-Earths, in orbits farther and farther from their suns.