In Proceeding of 5th Hellenic Astronomical Conference, Fodele 2001 Chaos at moderate eccentricities for the 2:1 resonant asteroid motion.

The formation of the Hecuba gap close to the 2:1 resonant asteroid mean motion with Jupiter is examined. We consider a symplectic mapping model and its phase space dynamics is studied by using spectral maps. It is shown that fast diffusion is possible even inside the region of moderate eccentricities (0.2- 0.5) and low inclinations where previous studies indicate islands with ordered motion. 1 The Model In the last decades, the explanation of the Kirkwood gaps is studied within the framework of the restricted 3 (or 4) body problem and it is traced back to the existence of chaotic motion. The reader can find more details about the topic of resonant asteroid dynamics in [1, 2]. Since the numerical integration of the equations of the original system are cpu-time consuming, generally, approximations of the models are used in order to study the long term evolution of asteroids. Our model is constructed by considering the following approximations: Averaging [3] The Hamiltonian of the original system, is written as a perturbe