June 18, 1999 The most precise measurement to date of the carbon monoxide to water ratio in a comet is reported by a team of astrophysicists in the June 17 issue of Nature. The article suggests that the comet Hale-Bopp was likely formed in the region between Jupiter and Neptune some 4 billion years ago.
The researchers, from the University of Notre Dame, NASA's Goddard Space Flight Center, and Rowan College in New Jersey, made their observations of the giant comet Hale-Bopp in 1997-1998 using an infrared spectrometer on NASA's three meter telescope at the Infrared Telescope Facility at the Mauna Kea Observatory in Hawaii. They determined that the carbon monoxide/water ratio was 12 percent.
"It's fundamentally important to know the amount and source of carbon monoxide," says Terrence W. Rettig, associate professor of physics at Notre Dame, who participated in the observations. "These data provide our most comprehensive clues about where and how Hale-Bopp was formed and give us a better understanding of its history."
According to Rettig, Hale-Bopp has spent most of its life in a deep freeze at great distances from the sun. It returned to the inner solar system recently in a sling-shot-like orbit, providing astronomers an opportunity for detailed examination. The comet will not return for another 10,000 years.
"Astronomers have been studying the visible attributes of comets for hundreds of years but until recently, infrared observations were not possible," says Rettig, "In the past several years, infrared detectors have become much more efficient, making these observations now possible."
This new observational technique, the unusually large size of Hale-Bopp and the closeness by which it passed earth during it's recent orbit around the sun all combined to provide the most precise measurements to date of carbon monoxide and water in a comet.
"Comets are interesting because they are frozen relics from the formation of our solar system, and by studying them, we can learn more about how we got here," says coauthor Michael Mumma, a scientist at Goddard.
Comets, essentially dirty snowballs, range in size from a few miles to dozens of miles across. The ice in comets is predominantly carbon monoxide and water, and knowing the exact composition of the icy structure helps scientists pinpoint its origin.
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