AWARDEE OF ASTRONOMY PRIZE

SUN YISUI

Abstract

Sun Yisui, born in Rui'an county, Zhejiang Province, specialist in celestial mechanics, graduated from Department of Astronomy, Nanjing University in 1958. He is a professor of astronomy at Nanjing University, and the chief scientist of National Nonlinear Science Project. He was elected  the academician of the Chinese Academy of Science in 1997.
His research work is mainly in the field of qualitative and nonlinear theory of celestial mechanics. In collaboration with X.Y.Chen et al., Sun obtained sufficient and necessary conditions for the variation ranges of orbital elements in the three-body problem for given positions of three bodies, thus solved the problem of variation range on the orbital shape and space location of three bodies for given positions of three bodies. In collaboration with C.Marchal et al., he found that the greatest lower bound of the moment of inertia for the elliptic Euler solutions of the three-body problem is also the greatest lower bound for all bounded solutions of the same masses and angular momentum. He first studied the conservative system without Hamiltonian structure and discovered the existence of two-dimensional invariant tori and periodically invariant curves in near-integrable volume-preserving maps with three dimensions. Later he and C.Q.Cheng gave an exact mathematical proof for this result. From this result negative answers for following two famous conjectures can be derived: the quasi-ergodic conjecture about conservative systems and Pesin's conjecture of the non-zero Lyapunov exponents for volume-preserving maps.