“After 20 years of exploring planets as big as Jupiter around other suns, we still have a lot of questions left open. For instance, we don’t understand what is the physical mechanism that forms Jupiter-like planets with orbital periods as little as a few days.” -Alexandre Santerne
By surveying an area of the sky containing over 150,000 stars visible to it, the Kepler satellite monitored each one over a multi-year period looking for periodic changes in brightness. Thousands of planetary candidates emerged via the transit method, where periodic dips of 3% or less were noted with regularity.
Go read the whole thing, and think about what it means. Perhaps our lone star Solar System is the oddity, after all.