Title: From Giotto to Rosetta Cometary Nuclei - a Personal View

Speaker: Professor Horst Uwe Keller (IGEP Universit？t Braunschweig & Institut für Planetenforschung DLR Berlin)

Time: 9:30am, May 17, 2024

Location: 3-302, PMO Xianlin Campus

Abstract: Their activity sets comets apart from all other planetary bodies. They often produce grandiose appearances on the sky when heated by the sun. Ground-braking interpretations in the middle of the last century characterized the tiny kilometer-sized cometary nuclei well enough to enable targeting the first European (ESA) space mission Giotto at comet Halley in 1986. The nature of cometary nuclei - well preserved relicts from the times of planetary formation - changed from "dirty snowball" to "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 makes it difficult to understand the physical processes that drive cometary activity. Over the following 20 years several NASA flyby missions investigated cometary nuclei further while Europe pushed its cornerstone mission Rosetta to rendezvous a comet. The two years long intensive observations of comet 67P from the onset of its activity to its maximum around perihelion and beyond revealed unprecedented details of the nucleus but did not yet solve the conundrum of its activity.