Comet of the Century?
July 26, 2013
A new image of Comet ISON taken by the Hubble Space Telescope is giving the public a tantalizing preview of what the deep-space traveler may look like when it makes its maiden voyage around the sun in late November. Some astronomers think the comet could outshine the full moon, rivaling the display put on by the Great Comet of 1860. That comet could be seen during daylight hours without a telescope. However, other researchers caution that the comet could fizzle, the way Comet Kohoutek did in 1973. So-called sungrazing comets like ISON often break up or boil during their perilously close passage by the sun. ISON will zip by the solar surface at a distance of only 724,000 miles (1.16 million kilometers). The comet might not even make it that far, given the hazards of travel through the Main Belt (also known as the Asteroid Belt) and inner solar system. One thing is certain, though–the comet will not crash into Earth.
An image of Comet ISON taken when it was 363 million miles (584 million kilometers) from the sun is actually a mosaic of images that simulates the way the comet would look if we could see with the same resolution as Hubble. NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Comet ISON was discovered in September 2012 by Russian astronomers while it was between the orbits of Jupiter and Saturn. It is named for the International Scientific Optical Network, a group of observatories in 10 countries. At this point, the nucleus of the comet is is less than 3 miles (5 kilometers) in diameter, though its dusty head is much larger—about 3,100 miles (5,000 kilometers) across. Its tail is an amazing 186,400 miles (300,000 kilometers) long, thanks to the prodigious amount of carbon dioxide escaping from the comet each day. Infrared observations made by American scientists using the Spitzer Space Telescope revealed that 2.2 million pounds (1 million kilograms) of carbon dioxide are “fizzing” away from the “soda-pop” comet daily. ISON is also shedding 120 million pounds (54.4 million kilograms) of dust.
Astronomers believe Comet ISON began its journey toward the sun from the Oort cloud, a cluster of comets, smaller objects, and perhaps even planets in the outermost region of our solar system. Scientists believe comets preserve leftover ice, rock, and dust from the solar system’s formation. As such, they provide valuable information about the history and composition of the solar system.
Additional World Book articles:
- Halley’s comet
- Meteor
- Stardust
- When Worlds and Comets Collide (a special report)
