Aerogel, sometimes nicknamed “frozen smoke,” is a type of solid, translucent foam material that is almost completely (about 99.8 percent) air. It can be made out of different substances, such as silica, carbon, or alumina (aluminum oxide). It is the lightest solid substance manufactured by humans, yet it has remarkable thermal insulating properties and structural strength. Spacecraft designers often use Aerogel to insulate their payloads (such as the Mars Exploration Rovers). Aerogel was the perfect substance to use in the Stardust mission to catch speeding cometary and interplanetary particles without causing them to be destroyed, either by the impact or the heat caused by friction.