Earth's companion is so large and fascinating that geologists count the Moon as one of the solar system's "terrestrial planets." In fact, it was probably born from Earth, after a Mars-sized body collided with the proto-Earth, in a collision so violent that the Moon that coalesced from the leftover fragments was entirely (or almost entirely) molten. We can tell this story of Earth and the Moon's creation thanks to our analysis of the rocks returned to Earth by the Apollo astronauts, Luna landers, and chance discoveries of lunar meteorites. New laboratory techniques yield new discoveries every year even though no samples have been collected from the surface of the Moon since 1972.
In the years since the end of the space race between the United States and Russia, many other nations have sent robotic spacecraft to orbit the Moon as a first step in their planetary exploration: Japan, the European Space Agency, India, and China. Likewise, many people see a staging station on the Moon as a necessary first stepping stone toward sending humans on missions to asteroids or Mars. Thanks to the combined data from lunar orbiters from all nations we know that there is water stored in lunar soil and that there are permanently sunlit peaks at the lunar poles, providing for two basic needs of human settlements: water and power. We can go back to the Moon; but who will make the effort?
