More than 300 extrasolar planets have been detected over the past dozen years, in orbit around more than 200 individual stars. The vast majority are located within 100 parsecs (326 light years) of our Sun. The current sample of exoplanetary systems is limited by observational technologies and biased in favor of massive planets orbiting nearby stars.

These alien systems bear little resemblance to our own. Their planets are unexpectedly massive – sometimes two, three, or four times the size of Jupiter, up to the uncertain limit separating planets from brown dwarf stars. Their orbits are unexpectedly tight, with many known exoplanets traveling in "torch" orbits within a few million miles of their host stars. For example, the planetary system of GJ 876 contains three planets whose aggregate mass substantially exceeds that of all eight planets in the Solar System. Yet the orbit of the outermost planet of GJ 876 is only half the size of the orbit of Mercury, the smallest planet in the Solar System with the tightest orbit.

The population of known exoplanetary systems is explored in detail on the pages linked here, with special emphasis on systems located in the immediate Solar neighborhood – here defined as the region of space within 65 light years (20 parsecs) of the Sun. This small sphere contains seven of the nine extrasolar systems known to contain three or more planets, as well as four systems with exactly two detected planets. It also contains several stars with debris disks analogous to the Asteroid and Kuiper Belts of the Solar System, along with more exotic exosystems containing binary stars, white dwarfs, and red giants.