KentuckyFC writes "The only planets never to have been the subjects of bespoke space missions from Earth are Neptune and Uranus. Now European astronomers are planning to put that straight with a mission called Odinus, which involves twin spacecraft making the journey in 2034. Their justification is that the mission will help explain how the Solar System formed, how it ended up in the configuration we see today and may also explain why 'hot' Neptune-class planets are common around other stars. They also have to overcome the common misconception that Neptune and Uranus are just smaller, less interesting versions of Jupiter and Saturn. Nothing could be further from the truth. For a start, Neptune and Uranus and made of entirely different stuff--mostly ices such as water, ammonia and methane compared with hydrogen and helium for Jupiter and Saturn. That raises the question of how they formed and how they got to the distant reaches of the Solar System. However it happened, Uranus ended up lying on its side, probably because of a cataclysmic collision. And Neptune's largest moon Triton orbits in the opposite direction to its parent's rotation, the only moon in the Solar System to do this. How come? Another question still unanswered is who's going to pay for all this. The team are pinning their hopes on the European Space Agency which has already expressed interest. But would an international collaboration be a better option?"