The impossible planet
The constellation Ursa Minor is home to a planet that cannot exist. At far too close a distance, Halla orbits the red giant star Baekdu. When Baekdu inflated in its previous expansion phase, it should have "swallowed" such a close companion. No other planets orbiting similarly near a red giant star are known. In today's issue of the journal Nature, an international team of 42 researchers led by the University of Hawaii describes the unusual pair and presents extensive calculations of its possible evolution. The computer simulations, to which a researcher from the Max Planck Institute for Solar System Research (MPS) in Göttingen contributed, provide an intriguing explanation. Most likely Baekdu was once a binary star – and Halla never in any danger.
