SPACE CENTER, Houston – NASA scientists have a new mystery to solve: How did materials formed by fire end up on the outermost reaches of the solar system, where temperatures are the coldest? The materials were contained in dust samples captured when the robotic Stardust spacecraft flew past the comet Wild 2 in 2004. A 100-pound capsule tied to a parachute returned the samples to Earth in January. The samples include minerals such as anorthite, which is made up of calcium, sodium, aluminum and silicate; and diopside, made of calcium magnesium and silicate. Such minerals only form in very high...