Hubble’s Best View of a Planetary Disk

At one point in history, let’s say around 1994, astronomers were fairly confident in their understanding of the formation of planetary systems.  Even though at the time we hadn’t found any planets orbiting other stars, they had long been theorized, and we figured that systems would form much like our own solar system.  Rocky planets in the interior, gaseous giants further out, and a huge icy debris field at the outer edges. And then along came 51 Pegasi b.  Half the mass of Jupiter, it orbits its star in only 4 days, far closer than Mercury.  It was considered a...