Coupled Escape Probability for an Asymmetric Spherical Case: Modeling   Optically Thick Comets
  We have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, for use in asymmetrical spherical situations. Our model is intended specifically for use in modeling optically thick cometary comae, although not limited to such use. This method enables the accurate modeling of comets' spectra even in the potentially optically thick regions nearest the nucleus, such as those seen in Deep Impact observations of 9P/Tempel 1 and EPOXI observations of 103P/Hartley 2. 
Alan M. Gersch and Michael F. A'Hearn
astro-ph.EP astro-ph.IM