Just possibly this is the biggest science story right now. http://www.theguardian.com/science/2015/jan/18/two-undiscovered-planets-earth-solar-system
Planet hunting so far has meant planet hunting in other solar systems, in the so called Goldilock zone, where planetary mass and distances from the suns would indicate a life-friendly place, where an atmosphere can be formed that retains potential water. Some 50 candidates have been discovered so far by Kepler. But a further 8 billion such exoplanets are estimated to exist. If ET is out there, it is on one of these.
Our own solar system however, was deemed as fixed, already explored. The maps were drawn, and children were learning the My-Very-English-Mother-Just-Showed-Us- Nine-Planets to memorize the names of the planets.
This discovery, however, tells us there is more to our planetary back yard than meets the telescopic eye.