Returns to Mercury: science and mission objectives

As the inner end-member of the planetary system, Mercury plays an important role in constraining and testing dynamical and compositional theories of planetary formation. With its companions Venus, Earth and Mars, it forms the family of terrestrial planets, a category of celestial objects in which each member holds information essential for retracing the history of the whole group. For example, knowledge about the origin and evolution of these planets is one of the keys to understanding how conditions to support life have been met in the Solar System and, possibly, elsewhere. This quest is all the more important as terrestrial-like objects orbiting other stars are not yet accessible; our own solar system remains the only laboratory where we can test models that are also applicable to other planetary systems. The exploration of Mercury is therefore of fundamental importance for answering questions of astrophysical and philosophical significance, such as: ‘Are terrestrial bodies a common feature of most planetary systems in the Galaxy?’