Light Echoes Used to Study Protoplanetary Disks This illustration shows a star surrounded by a protoplanetary disk. A new study uses data from NASA’s Spitzer Space Telescope and four ground-based telescopes to determine the distance from a star to the inner rim of its surrounding protoplanetary disk. Researchers used a method called „photo-reverberation,“ also known as „light echoes. via NASA http://ift.tt/26rHbbb