One reason researchers have long believed that Marsnever enjoyed an extensive period of warm and wetclimate is that much of the surface not covered bywind-borne dust appear to posed ofunweathered material. If water flowed for anextended period, researchers reasoned, it shouldhave altered and weathered the volcanic minerals,creating clays or other oxidized, hydrated phases(minerals that incorporate water molecules in theircrystal structure).
It turns out, though, that the scientists were notlooking closely enough. New high-resolution mapping data and close-up surface studies haverevealed clays and other hydrated minerals in many regions. The clay deposits are scattered allover, in ancient volcanic surfaces and heavily cratered highland regions, some of which haveapparently been exposed by erosion only recently.