The Australian discovery of a strange exoplanet orbiting a small cool star 500 light years away is challenging ideas about how planets form. "We have found a small star, with a giant planet the size of Jupiter, orbiting very closely," said researcher George Zhou from the Research School of Astrophysics and Astronomy. "It must have formed further out and migrated in, but our theories can't explain how this happened." In the past two decades more than 1,800 extrasolar planets (or exoplanets) have been discovered outside our solar system orbiting around other stars. The host star of the latest exoplanet, HATS-6,...