ESA's Bepi Colombo, the dual spacecraft mission to Mercury, conducted in partnership with Japan, is one of the most challenging ever decided.
It is due to be launched by the Ariane rocket in 2014, and will take six years to reach its target.
The programme has just passed a significant milestone with the completion of the first crucial thermal tests at ESA's technical and research centre in the Netherlands.
ESA's planetary missions can go from one extreme to another.
Whilst the Rosetta comet probe pursues its journey in the cold depths of deep space, its solar panels having to retain the weak rays of our distant Sun, BepiColombo will be braving the infernal heat around the innermost planet, less than 40 million miles from the sun.
Scientists hope to answer many question about Mercury, such as is its core liquid or solid? They also want to know the origin of the many long marks across its surface, and whether there could be water and ice at the poles of this intensely hot planet.