Venus Express will be ESA's first mission to Earth's nearest planetary neighbour, Venus. The mission was born after ESA asked for proposals, in March 2001, suggesting how to reuse the design of the Mars Express spacecraft.
The guidelines were extremely strict. The mission would have to run to a tight timeframe because it had to reuse the same design as Mars Express, and the same industrial teams that worked on that mission. It would have to be ready to fly in 2005.
Out of a number of promising proposals, ESA selected Venus Express. What made the mission especially attractive was that many of the spare instruments developed for ESA's Mars Express and Rosetta missions could be used to achieve Venus Express's science objectives, which were to study the atmosphere in great detail
1 - Why Venus ?
2 - World of mysteries