Combined data from NASA’s Spitzer Space Telescope, the Hubble Space Telescope and the Chandra X-ray Observatory reveal the false-color remains of an exploded star called Cassiopeia A, which is 10,000 light-years from Earth and measuring 13 light-years across. Because it is so young and so close to Earth, experts consider Cassiopeia A an excellent source for the study of supernovas. When a star such as Cassiopeia A explodes, its remnants are shot out into space. This means elements such as oxygen, sulfur and iron expand beyond their original source. Heated gas and material from the star create a glowing shell. Judging from the size of its expanding gas cloud, scientists think Cassiopeia A exploded about 333 years ago.