NASA said it is recycling two used spacecraft to lead new robotic missions to study comets and planets around other stars. The encore performances of the Deep Impact and Stardust probes allow the space agency to further its solar system exploration for a fraction of the cost it would take to start a mission from scratch. Both spacecraft successfully completed their primary missions to two different comets and their discoveries have helped scientists understand how the solar system formed. In 2005, Deep Impact released a copper impactor that smashed into comet Tempel 1. The collision carved a crater and spilled a plume of debris from its interior into space. The surviving mothership has since been put in safe mode to conserve energy.