Can planets exist in a binary or multiple system? Have scientists ever discovered such a solar system?
Yes, they can! But not on any kind of orbit and not in any kind of a binary system. Binary system planets come in two different types: planets that orbit just one of the binary components (called S-type orbits) and planets that orbit both of the binary components (called P-type orbits).
For S-type systems where the planet just orbits one star, the planet is typically much closer to its parent star that the distance between the two stars. Any planets that would sometimes get too close to the other sun are expected to have unstable orbits that would eventually put them on collision course with one of the stars. It should be noted that, while most binaries in which planets have been found had exceptionally large separation between stars (like in 16 Cygni and Upsilon Andromedae systems), this might be due to an observational bias. Usually, "planet hunters" go either for single stars or very wide binaries, where there is little interference from the companion, since planets are easier to detect in those cases. The discovery of the first planet in a relativly close binary system was made by William Cochran and his team (at McDonald Observatory in Texas; here is the link (you can read their press release here).
Planets from P-type systems, often called circumbinary planets or "Tatooine planets", are usually found orbiting their two stars at a distance much greater than the separation between the stars themselves. You can read about the first planet of this type discovered, Kepler-16b (nicknamed "Tatooine"), here. Since this discovery many planets of this type have been discovered.
Page last updated on July 18, 2015.