‘Soda pop’ comet has tons of sizzle

JOHNS HOPKINS (US) — NASA’s Spitzer Space Telescope has spotted what are most likely tons of carbon dioxide fizzing away from the so-called “soda-pop comet” as it approaches its rendezvous with the sun later this year.

Images captured June 13 with Spitzer’s Infrared Array Camera indicate carbon dioxide is steadily evaporating away from Comet ISON, along with dust, in a tail about 186,400 miles long.

“We estimate ISON is emitting about 2.2 million pounds of what is most likely carbon dioxide gas and about 120 million pounds of dust every day,” says Carey Lisse, leader of NASA’s Comet ISON Observation Campaign.

The Hubble Space Telescope and two other NASA missions had previously allowed researchers only to calculate the maximum amount of gas that might be spewing from the comet.

The image on the left shows a tail of fine rocky dust issuing from the comet and blown back by the pressure of sunlight as the comet speeds toward the sun. The image on the right, taken at a longer wavelength and with the dust removed, reveals a neutral gas atmosphere, most likely carbon dioxide “fizzing” from the surface. (Credit: NASA/JPL-Caltech/C. Lisse, JHUAPL/Y. Fernandez, UCF)

“Thanks to Spitzer, we now know for sure the comet’s distant activity has been powered by gas,” says Lisse, a senior research scientist at the Johns Hopkins University Applied Physics Laboratory.

Comet ISON was about 312 million miles from the sun, 3.35 times farther than Earth, when the observations were made.

“These fabulous observations of ISON are unique and set the stage for more observations and discoveries to follow as part of a comprehensive NASA campaign to observe the comet,” says James L. Green, NASA’s director of planetary science. “ISON is very exciting. We believe that data collected from this comet can help explain how and when the solar system first formed.”

Comet ISON (officially known as C/2012 S1) is less than 3 miles in diameter, about the size of a small mountain, and weighs between 7 billion and 7 trillion pounds. Because the comet is still very far away, its true size and density have not been determined accurately.

Inbound from Oort Cloud

Like all comets, ISON is a dirty snowball made up of dust and frozen gases such as water, ammonia, methane and carbon dioxide. These are some of the fundamental building blocks which, scientists believe, led to the formation of the planets 4.5 billion years ago.

Comet ISON is believed to be inbound on its first passage from the distant Oort Cloud, a roughly spherical collection of comets and comet-like structures that exists in a space between one-tenth light-year and 1 light-year from the sun.

The comet will pass within 724,000 miles of the sun on November 28. As it approaches the inner solar system and gradually warms up, increased evaporation is expected to reveal even more of the comet’s composition. NASA will continue to study the comet with earth- and space-based instruments.

Carbon dioxide, the gas that gives sodas their fizz, is thought also to be the gas that powers emission for most comets between the orbits of Saturn and the asteroids.

ISON was discovered Sept. 21, roughly between Jupiter and Saturn, by Vitali Nevski and Artyom Novichonok at the International Scientific Optical Network (ISON) near Kislovodsk, Russia.

“This observation gives us a good picture of part of the composition of ISON, and, by extension, of the proto-planetary disk from which the planets were formed,”  Lisse says.

“Much of the carbon in the comet appears to be locked up in carbon dioxide ice. We will know even more in late July and August, when the comet begins to warm up near the water-ice line outside of the orbit of Mars, and we can detect the most abundant frozen gas, which is water, as it boils away from the comet.”

NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate in Washington.

Source: Johns Hopkins University

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