It's our nearest neighbor and a near twin to Earth in size and composition. But, compared to the rest of the terrestrial worlds, we know little about Venus. What makes the markings in its clouds? How did its history diverge from Earth's to lead to its hellish climate? Why does it have so many volcanoes? Are any of those volcanoes active today? What is its surface made of? Current missions like Venus Express and Akatsuki aim to understand its atmosphere, but no one is currently planning to venture beneath its clouds to explore its surface.
