Mercury is the least explored of the four rocky planets of the inner Solar System. So far only two missions, NASA's Mariner 10 and MESSENGER, visited this Moon-like world that is so close to the Sun that temperatures on its surface regularly reach over 400°C. In 2011, MESSENGER was the first and so far only satellite to enter into orbit around Mercury. Its data revealed a world much more perplexing and complex than scientists had expected. BepiColombo, the joint mission by ESA and the Japan Aerospace Exploration Agency (JAXA), might shed light on some of the unresolved mysteries of the innermost planet of the Solar System.