PHYSICS IV 2011 Postcard from the Edge of the Solar System: Cassini’s Ringside View of Mira

Mira is the prototype for a class of pulsating red giant stars whose dense slow winds account for 75% of material enriching the interstellar environment. This grand galactic recycling scheme sees dying stars expelling matter which fuels subsequent generations of starbirth, and critically for us, provides heavy elements to form rocky planets and the chemical ingredients necessary for a biosphere. Surprisingly, after decades of debate, there remains no consistent picture of the basic physics of the wind launch process, with progress hampered by the lack of incisive observational data at the scale of the extended molecular atmosphere and wind base. Here we present novel observations utilising the Cassini spacecraft to conduct the first observing campaign for stellar astronomy from the outer solar system. By exploiting occultation events in which Mira passed behind the Saturnian ring plane as viewed by Cassini, imaging data was recovered spanning the near-infrared from 1-5 microns. From this, high angular res-olution spatial information more than an order of magnitude better than any previously published work was recovered. These findings have been contrasted against predictions from the present state-of-the-art physical models for the structure of the molecular atmosphere of Mira.