Death of a Comet:
What We Learned from the Passing of ISON
Why the celestial object did not survive its close brush by the sun
By Clara Moskowitz
Scientists were less than thankful this year on Thanksgiving Day (November 28) when they watched the famous Comet c/2012 S1, aka ISON, expire during its fiery pass by the sun. Yet seeing ISON meet its fate taught researchers about the structure and composition of the comet and gave them a clearer picture of why it broke up near the sun.
Comet ISON was a rare interloper in the inner solar system from the faraway Oort Cloud, a sphere of comets that surrounds the sun and planets about a light-year away. Its trajectory brought it within just three solar radii of the sun’s surface, putting it in a class of brazen comets called “sun grazers.” “We’ve never seen an Oort Cloud [castoff] sun-grazing comet before,” Karl Battams of the Naval Research Laboratory in Washington, D.C., said during a postmortem press conference Tuesday at the American Geophysical Union meeting in San Francisco. “It was an unprecedented object.”
Discovered just last September, ISON’s flight toward the sun prompted an observing campaign grander than any comet watch before. Telescopes all over the world as well as 13 space observatories and hundreds of amateur astronomers trained their sights on ISON over the past several months.