In this image made on Oct. 9, comet ISON’s atmopshere, or coma, has been removed, leaving behind the nucleus. (NASA, ESA, the Hubble Heritage Team (AURA/STScI) and Jian-Yang Li (Planetary Science Institute))
NASA’s Messenger spacecraft took this image of comet ISON during its closest approach to Mercury on Nov. 20. (ASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Southwest Research Institute)