Mercury, the closest planet to the Sun, remains somewhat of a mystery to us.
In the past, because of its proximity to the Sun, it has been difficult for Earth-based telescopes to observe Mercury against the ferocious solar light. In 2015, to increase our understanding of this mysterious planet, Europe is launching BepiColombo, the first dedicated mission to Mercury. It will reach its destination in 2022.
Its observations of Mercury should also offer new insights into the workings of extra-solar planets in other solar systems. These planets, which like Mercury are formed in very close proximity to their parent star the sun, are a hot topic in planetary science and astronomy at the moment.
More background information can be found on: http://www.esa.int/esaSC/index.html