These NASA Spitzer Space Telescope (SST) images of C/2012 S1 (Comet ISON) were taken on June 13, when ISON was approximately 310 million miles from the sun. The images were taken with SST’s Infrared Array Camera at two different near-infrared wavelengths, 3.6 and 4.5 microns (the false colors shown were selected to enhance visibility). The 3.6-micron image on the left side shows a tail of fine rocky dust issuing from the comet and blown back by the pressure of sunlight as the comet speeds toward the sun (the tail points away from the sun). The image on the right side shows the 4.5-micron image with the 3.6-micron image information (dust) removed, and reveals a very different round structure, the first detection of a neutral gas atmosphere surrounding ISON. In this case, it is most likely created by carbon dioxide that is “fizzing” from the surface of the comet at a rate of about 2.2 million pounds a day.
With a nucleus less than 2 miles in diameter and weighing between 7 billion and 7 trillion pounds, Comet ISON (officially known as C/2012 S1) is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide — some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. ISON will pass within 724,000 miles of the sun on Nov. 28, making it a sungrazer comet that will evaporate its ices and even its rocky dust near perihelion, revealing even more of the comet’s composition.
NASA is bringing to bear a vast fleet of spacecraft, instruments, and space- and Earth-based telescopes to study this rarely seen type of comet over the next year. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences.
The complete list of observers is: C. M. Lisse, R. J. Vervack, and H. A. Weaver, Johns Hopkins University Applied Physics Laboratory; J. M. Bauer, Jet Propulsion Laboratory/Caltech; Y. R. Fernandez, University of Central Florida; M. S. P. Kelley, University of Maryland; M. M. Knight, Lowell Observatory; D. Hines, Space Telescope Science Institute; J-Y Li, Planetary Science Institute; W. Reach, USRA/SOFIA; M. L. Sitko, University of Cincinnati; P. A. Yanamandra-Fisher, SSI; K. J. Meech and J. Rayner, University of Hawaii.
Image Credit: NASA/JPL-Caltech/C. Lisse (JHUAPL)/Y. Fernandez (UCF)
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