My auxiliaries are the dews and rains which water this dry soil, and what fertility is in the soil itself, which for the most part is lean and effete. Henry David Thoreau, Walden Pond The concerns that Thoreau had about his beans were nothing to those that would face a similarly conscientious gardener in the Atacama Desert or on the planet Mars, where dews are rare, or frozen, and rains are extremely rare or absent al- gether. Yet we live in a time when an appreciation of the differences and simila- ties among soils (or regolith: no organics detected on Mars, as yet ) can provide a...