Fizzy Comet ISON puttin' on the spritz

Holy carbonated comets Batman! NASA's Spitzer Space Telescope took a look at Comet ISON on June 13 and...

Holy carbonated comets Batman! NASA's Spitzer Space Telescope took a look at Comet ISON on June 13 and observed a gassy atmosphere created by frozen carbon dioxide ice slowly fizzing away in sunlight.

Spitzer sees the sky in infrared, a "color" just beyond the red end of the rainbow spectrum. We can't see infrared with our eyes but our skin senses it as heat. Interstellar dust and comet dust alike give off a warm glow in the infrared.

Spitzer snapped two views ISON; the image on the left was taken through a filter sensitive to the light emitted by warm rock dust and shows a distinct tail blown back from the comet's head by the pressure of sunlight. The image on the right was made through a slightly longer wavelength filter (deeper in the infrared) that gives us a better view of the comet's vaporizing gases. Scientists are reasonably certain the gas is carbon dioxide "fizzing" off ISON's nucleus at the rate of 2.2 million pounds (1 million kg) a day. That's a lot of champagne bubbles!


Frozen CO2 (dry ice) is a common ingredient found in many comets and one of the first ices to vaporize in the warm sunlight as a comet makes its trek toward the inner solar system. Spitzer's measurements now prove that ISON's early brightness surge was most likely due to the gas though frozen carbon monoxide is also a possibility. Thanks to the surge, amateur astronomers Vitali Nevski and Artyom Novichonok discovered the comet when it was still far away between the orbits of Jupiter and Saturn.

Comet ISON is a typical comet composed of various ices - water, CO2, ammonia, methane - and fine rock dust. On approach the sun, a comet's ice changes directly from solid to gas, a process called sublimation. Dust embedded in the ice goes along for the ride and soon forms a tail behind the comet. Right now, ISON's blowing off about 120 million pounds of dust every day.

The orbiting ice-ball measures a little under 3 miles (5 km) across and weighs between 7 billion and 7 trillion pounds but already sports a tail 186,400 miles (300,000 km) long. If a glacier could fly, it would resemble a comet ... with a few differences. Comets are black as coal; eons of bombardment by solar radiation and cosmic rays have grilled their organic chemicals to a dark pitch.

"The (Spitzer) observation gives us a good picture of part of the composition of ISON," said Carey Lisse, leader of NASA's Comet ISON Observation Campaign. "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."

After all this comet talk, I'm suddenly in the mood for something cold and fizzy.

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