Figure 4-12 RIVUXG Protoplanetary Disks (a) The Orion Nebula is a star-forming region located some 1500 ly from Earth. It is the middle “star” in Orion’s sword (see Figure 1-3). (b) This view of the Orion Nebula is a mosaic of Hubble Space Telescope images. The insets are close-ups of four protoplanetary disks that lie within the nebula. A young star with orbiting planets is forming at the center of each disk.