It’s make or break time for Comet c/2012 S1 (ISON), a ball of ice hurtling toward the inner solar system that will make its closest approach to the sun this month. Whether ISON will flare into a “great comet” or fizzle out is still an open question, but scientists say either way, ISON offers an unprecedented opportunity to understand the ingredients and history of the solar system.
Comet ISON was discovered in September 2012 by two Russian astronomers using telescopes in the International Scientific Optical Network (ISON). The comet, made mostly of water and carbon dioxide ice, has been slowly making its way toward the sun from the Oort Cloud, the roughly spherical cloud of comets thought to extend about a light-year from the sun, about a third of the way to the nearest star. The comet “is going from the absolute coldest place in the solar system to the absolute hottest,” says Matthew Knight, an astronomer at Lowell Observatory in Flagstaff, Ariz. The ISON comet, known as sungrazer, will make its nearest pass to the sun on November 28, Thanksgiving Day, flying close to the surface. “We’ve never had a comet that seems to come directly from the Oort Cloud, on its first passage to the inner solar system in four billion years, all the way to within three solar radii of the solar surface,” says astronomer Michael Kelley of the University of Maryland, College Park. Kelley has been part of several campaigns to image ISON using telescopes in Hawaii, Arizona and the Canary Islands.To read more, click here.