IGEP Universit？t Braunschweig Institut für Planetenforschung DLR Berlin

  Dr. Horst Uwe Keller‘s research fields include physics and dynamics of comets, stellar atmosphere, interplanetary/ interstellar gas, planetary atmospheres (Mars), atmosphere-surface interactions, photometric surface properties (asteroids, Titan), methods of image analysis. He was the PI for Halley multicolour camera onboard Giotto, SIR infrared spectrometer for SMART 1, the Rosetta OSIRIS science cameras and the Dawn FC camera.

  Awards and recognition: Dr. Horst Uwe Keller won Stern Gerlach Prize of the German Physical Society in 1990, Publication Award from the Naval Research Laboratory in 1992, German TV Prize "The Golden Lion” in 1997, Christiaan Huygens Medal of the European Geophysical Union in 2008 and several other awards from NASA and ESA.

  Abstract：Their activity sets comets apart from all other planetary bodies. It took hundreds of years to realize that comets are interplanetary bodies consisting of dust and volatiles. Ground-breaking interpretations in the middle of the last century made the tiny cometary nuclei well enough defined to target the first European (ESA) space mission at comet Halley in 1986. The nature of cometary nuclei - well preserved relicts from the times of planetary formation - changed from a “dirty snowball” to an “icy dirtball”. This change of paradigm was only slowly accepted but well confirmed by Deep Space, the next flyby mission 15 years after Giotto. The dominance of refractory material over the ice content makes it difficult to understand the physical processes that drive cometary activity. Over the following 20 years several flyby missions investigated cometary nuclei further while Europe pushed its cornerstone mission Rosetta to rendezvous a comet. The two years long intensive observations from the onset of cometary activity to its maximum around perihelion and beyond revealed unprecedented details of the nucleus. How do the new findings about the physics of cometary nuclei and their activity compare to the results of the flyby missions?