The Earth’s own Moon will play a critical role in the future of human exploration of the solar system. While some might quibble whether the Moon should lie in the critical path for future human missions elsewhere in the solar system, it’s clear under the Vision for Space Exploration that, at least for the US, the Moon will be not just a major goal for exploration, but a place to test some of the systems and technologies needed for missions to Mars and beyond. Less has been said, though, about the role of Mars’s own small moons, Phobos and Deimos,...