C/2007 Q3, Comet Siding Spring

- Image ID: HRJ7A2
Science History Images / Alamy Stock Photo
Image ID: HRJ7A2
Comet Siding Spring appears to streak across the sky like a superhero in this new infrared image from NASA's Wide-field Infrared Survey Explorer. C/2007 Q3 was discovered in 2007 by observers in Australia. The snowball-like mass of ice and dust spent billions of years orbiting in the deep freeze of the Oort Cloud, a spherical cloud of comets surrounding our solar system. At some point, it got knocked out of this orbit and onto a course that brings it closer to the sun. On October 7, 2009, it passed as close as 1.2 astronomical units from Earth and 2.25 astronomical units from the sun. Now, the comet is leaving the warmer, more hospitable neighborhood of the solar system and heading back out to chillier parts. In this view, 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, for example, the bright blue star in the foreground. Colder objects give off more of their light at longer wavelengths. In this image, 3.4-micron light is colored blue; 4.6-micron light is green; 12-micron light is orange; and 22-micron light is red. It was taken on January 10, 2010.