These images from NASA's Spitzer Space Telescope of C/2012 S1 (Comet ISON) were taken on June 13, when ISON was 310 million miles (about 500 million kilometers) from the sun. The images were taken with the telescope's infrared array camera at two different near-infrared wavelengths, 3.6 and 4.5 microns (the representational colors shown were selected to enhance visibility). The 3.6-micron image on the left shows a tail of fine rocky dust issuing from the comet and blown back by the pressure of sunlight as the comet speeds towards 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 (1 million kilograms) a day.

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 (1.2 million kilometers) 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.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer.

Learn more about NASA's Comet ISON Observing Campaign at http://www.isoncampaign.org and NASA's Comet ISON Toolkit at http://solarsystem.nasa.gov/ison.