LAUSR

We consider three point positive masses moving on S and H. An Eulerianrelative equilibrium, is a relative equilibriumwhere the threemasses are on the same geodesic, in this paper we analyze the spectral stability of these kind of orbits where the mass at the middle is arbitrary and the masses at the ends are equal and located at the same distance from the central mass. For the case of S, we found a positive measure set in the set of parameters where the relative equilibria are spectrally stable, and we give a complete classiûcation of the spectral stability of these solutions, in the sense that, except on an algebraic curve in the space of parameters, we can determine if the corresponding relative equilibria is spectrally stable or unstable. On H, in the elliptic case, we prove that generically all Eulerian-relative equilibria are unstable; in the particular degenerate case when the two equal masses are negligible we get that the corresponding solutions are spectrally stable. For the hyperbolic case we consider the systemwhere themass in themiddle is negligible, in this case the Eulerian-relative equilibria are unstable.