1. First MESSENGER orbital observations of Mercury's librations Stark, Alexander; Oberst, Jürgen; Preusker, Frank; Peale, Stanton J.; Margot, Jean-Luc; Phillips, Roger J.; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.; Solomon, Sean C. 2015 Articles Planetary sciencePlanets--OrbitsPlanets--Rotation