But the samples we collected from it we believe to be exactly the same materials that went into forming the comets and the solar system four and a half billion years ago.

NPR: Stardust Set to Deliver Comet Samples

Clays are water-loving materials (just ask any friends who make pottery), sometimes forming from the interaction of water and different kinds of precursor volcanic rocks, and holding much of that water within their mineral structures.

CNN: Have a drink on Mars