Title: "Space debris with high A/m : a web of secondary resonances. " Speaker: Prof. Anne Lemaitre The population of space debris is quite surprising; in particular, a sub-population, close to the geostationary orbit, was detected a few years ago, showing very large values of the eccentricity. Recent studies, in Namur and in different centers of research, showed that the responsible for these very eccentric behaviors was the solar radiation pressure, acting on bodies characterized by very high values of the coefficient A/m. The main effects of the solar radiation pressure can be modelized and reduced to (averaged) very simple formulae. Numerical investigations have also shown chaotic phenomena (deep dependence on the initial conditions) for such debris; a first analysis with the chaos indicator MEGNO revealed a choatic region along the separatrix of the geostationary resonance, with a width proportional to A/m, and a web of sub-structures, alterning stable and unstable zones, inside and outside the libration pendulum region. Confirmed and refined by the Frequency Map Analysis, these zones coincide with commensurabilities between the geostationary libration periods and the annual period of the Sun. Through the introduction of suitable action-angle variables in the pendulum problem, these secondary resonances have been identified, located and expressed as simple local pendulum models, with associated long resonance periods. Some of these stable layers could be reservoirs of space debris for some dozens of years.