Keller, H. U. Department Planets and Comets, Max Planck Institute for Solar System Research, Max Planck Society; MPI for Aeronomy, Max Planck Institute for Solar System Research, Max Planck Society;
Keller, H. U., & Jorda, L. (2002). The morphology of cometary nuclei. In J. A. M. Bleeker, J. Geiss, & M. C. E. Huber (Eds.), The Century of Space Science (pp. 1235-1275). Dordrecht, The Netherlands: Kluwer Academic Publishers.