Astronomers used the Hubble Space Telescope to take a sweet image of Comet ISON on April 10 when it was 394 million miles from Earth. This is the comet expected to put on a great show later this fall when it zooms just 680,000 miles from the sun.
Like most fresh arrivals from the distant comet repository known as the Oort Cloud, Comet ISON already shows good activity despite its great distance from the sun. Amazingly, even the feeble heat solar heat felt by the comet at its remote locale is enough to vaporize carbon monoxide and other exotic ices in the comet’s core.
Unlike the stuff that comes out of your refrigerator, comet ice is not pure but embedded with dust and rocky material. Think of dirty snow lining winter streets after the plow’s been by and you get the idea.Vaporized by sunlight, the icy stuff vaporizes into a large gassy/dusty coma centered on the comet body itself.
When the photos were shot, the coma measured 3,100 miles (5,000 km) across. Pressure from sunlight drives some of the gas and dust released from the comet back into a tail that extends 57,000 miles (92,000 km) in the direction opposite the sun – much of it reaches beyond the Hubble’s field of view. The blue false color was added to bring out details in the comet’s structure.
In the contrast-enhanced image, we can see a fountain of dust spewing from the sunward side of the ISON’s nucleus, the small, solid body at the comet’s core.
Solar heating opens up cracks or fissures in its icy-dusty surface, exposing fresh ice beneath. Eager to vaporize, the ice heats up, turns to gas and blasts out into space like a nonstop, explosive sneeze, carrying with it a load of embedded dust.
Careful analysis of comet jets can tell astronomers much about a comet’s shape and the spin of the solid nucleus. It’s nice to see NASA using the Hubble Space Telescope for this close up view; most pictures taken of late have been by amateur astronomers. While their much appreciated efforts show the same basic structure, the extra detail provided by Hubble makes ISON feel that much more real.