Astronomers at MIT, the University of Liège in Belgium, and elsewhere have discovered a huge, fluffy oddball of a planet orbiting a distant star in our Milky Way galaxy. The discovery, reported today in the journal Nature Astronomy, is a promising key to the mystery of how such giant, super-light planets form.The new planet, named WASP-193b, appears to dwarf Jupiter in size, yet it is a fraction of its density. The scientists found that the gas giant is 50 percent bigger than Jupiter, and about a tenth as dense —…