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Carbon monoxide discovered in Pluto’s atmosphere
Posted: 19 April 2011

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A two decade-long search for carbon monoxide in Pluto’s atmosphere has finally met with success thanks to a UK-lead team using the 15-metre James Clerk Maxwell Telescope.

Artist's impression of Pluto's huge atmosphere of carbon monoxide. The source of this gas is erratic evaporation from the mottled icy surface of the dwarf planet. The Sun appears at the top, as seen in the ultra-violet radiation that is thought to force some of the dramatic atmospheric changes. Pluto's largest moon, Charon, is seen to the lower right. Image: P.A.S. Cruickshank.

Pluto is the only dwarf planet known to have an atmosphere and until now, it was thought to be around 100 kilometres thick. The new data, collected from 70 hours worth of observations lead by Jane Greaves of the University of St Andrews, raises this atmosphere to 3,000 kilometres, a quarter of the way out to Pluto’s largest moon Charon. The signal of the -220 degrees Celsius carbon monoxide gas, which accounts for around one percent of the predominantly nitrogen-rich atmosphere, was twice as strong as an upper limit set by a team using the 30 metre IRAM telescope in Spain, back in 2000.

“The signature of the gas got brighter, and the speed at which it changed over the last decade was very surprising,” Greaves tells Astronomy Now. Pluto made its closest approach to the Sun in 1989, on its 248 year orbit around the Sun. “Perhaps Pluto’s atmosphere got warmer as the planet’s icy surface warmed and evaporated as it neared the Sun, boosting the carbon monoxide signal.”

Carbon monoxide acts as a coolant, whereas the small methane component of Pluto’s atmosphere is an absorber, which produces heating. The balance between the two gases is critical to its fate, and Pluto’s atmosphere is probably the most fragile in the Solar System, with the top layers blowing away into space. Whether or not the carbon monoxide component is sufficient to slow the atmospheric loss is yet to be determined, but the team plan to continue monitoring the distant world at least until the fly-by of New Horizons in 2015.

“The results provide a unique test bed to understanding climate and atmosphere in general, as well as provide important clues as to how some of the basic physics of atmospheric heating works,” adds Greaves.