Understanding why Earth’s closest neighbour, Venus, is so different

and the more recent Magellan, Venus Express, and Akatsuki Missions, Venus remains a global mystery. Sitting in our planetary back yard, Venus represents an unusual example of terrestrial planet formation and evolution that obviously differs from Earth and the other solid planets of the inner solar system. Many fundamental questions remain unanswered. For example, did Venus ever have oceans, how has its atmosphere evolved over time, and when and why did its runaway greenhouse begin ? How does Venus lose its heat, how volcanically and tectonically active has Venus been over the last billion years ? 

Thus, a key question in planetary science is why, despite being so similar, our next-door neighbour has experienced such a dramatic climate change?  When and why did Venus arrive at this state and does it foretell Earth’s fate should it, too, undergo a catastrophic greenhouse effect? What lessons could be learned about the evolution…