Comet Siding Spring
Date: 10 Jan 2010
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, or WISE. The comet, also known as 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 7 October 2009, it passed as close as 1.2 astronomical units from Earth and 2.25 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth). Now, the comet is leaving the warmer, more hospitable neighborhood of the solar system and heading back out to chillier parts.
In this image, taken on 10 January 2010, 3.4-micron light is colored blue; 4.6-micron light is green; 12-micron light is orange; and 22-micron light is red. 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. An ice cube, for example, pours out a larger fraction of its light at longer infrared wavelengths than a cup of hot tea emits.
A comet like this one can be thought of as a time capsule leftover from the formation of our solar system 4.5 billion years ago. After spending most of its long, lonely life in the darkest, coldest parts of our solar system, it warms up as it approaches the sun. The sunlight causes it to shed ices and dust in a long tail that trails behind it.
WISE data on this and other comets will help unlock clues that lay within these icy time capsules, teaching us about our solar system's evolution.
Last Update: 29 Mar 2011 (AMB)
Credit: NASA/JPL-Caltech/WISE Team