Comet ISON’s disintegration into a cloud of debris as it neared its closest approach to the sun on 28 November came as no surprise to astronomers. They knew the kilometer-size “dirty snowball” or nucleus at the heart of the comet had never been tested by the rigors of a passage through the inner solar system. And no icy comet nucleus was all that sturdily built eons ago during the formation of the planets. So its frustratingly unpredictable lulls and flare-ups  as it spewed gas and dust under the sun’s glare fit astronomers’ expectations. But when it emerged from its brush with the sun, ISON was obviously transformed . Astronomers now believe that the sun’s searing heat and its wrenching tidal pull—stretching the nucleus like so much putty—did in the nucleus hours before its closest approach to the sun. In this time-lapse image from the orbiting SOHO spacecraft, the debris cloud continues past the sun in ISON’s orbit, yielding an ever-diminishing amount of gas and dust. Today, it is far too faint for the naked eye to perceive and fading fast. Let the data analysis begin.
ScienceShot: First-Time Comet Perishes
Richard A. Kerr