Comet Siding Spring, infrared image. This comet, also known as C/2007 Q3, was discovered in 2007 by observers in Australia. On 7 October 2009, it passed near the Earth and Sun. Longer wavelengths of infrared light are red and shorter wavelengths are blue. The comet appears red because it is more than ten times colder than the surrounding stars. Comets like this one date from the formation of the solar system 4.5 billion years ago. This image is from NASA's Wide-field Infrared Survey Explorer (WISE). The WISE measurements revealed the comet's size, composition, and reflectivity. Image obtained on 10 January 2010.
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