As of this Monday, 760 exoplanets have been identified since 1992 (thanks, Wikipedia!), almost all within 300 light-years of us -- a small fraction of our galaxy. Some of them even orbit Sun-like stars, and some of those within the habitable zone. This is, of course, IMMENSELY COOL. First citation for the term is from 1994, coined from Greek root exo-, outer, external + planet, itself from Greek planētēs, from planēs, wanderer -- in the sense of a wandering star, as opposed to the fixed stars of the sky.
Searching for exoplanets is one of the hottest fields of astronomy these days, and I strongly urge you to have your son specialize in it.