Cold Cloud Of Toxic Hydrogen Cyanide Discovered Above South Pole Of Titan

Chuck Bednar for redOrbit.com – Your Universe Online
Analysis of data collected by NASA’s Cassini mission has revealed the presence of a large, cold, toxic cloud swirling above the south pole of Saturn’s moon Titan, according to research published in the October 2 edition of the journal Nature.
According to the US space agency, scientists from the Leiden Observatory in the Netherlands, the SRON Netherlands Institute for Space Research, the University of Bristol’s School of Earth Sciences, the LESIA-Observatoire de Paris and the Oxford University Department of Physics found that the giant polar vortex contained frozen particles of the toxic compound hydrogen cyanide (HCN).
“The discovery suggests that the atmosphere of Titan’s southern hemisphere is cooling much faster than we expected,” lead author Dr. Remco de Kok of Leiden Observatory and SRON Netherlands Institute explained in a statement Wednesday.
Titan is the only moon in the solar system that has a dense atmosphere, and like Earth it experiences seasons, the researchers explained. It takes 29 years to travel around the sun along with Saturn, and each of those seasons last approximately seven Earth years. The most recent season change took place in 2009, when spring took over for winter in the northern hemisphere and summer became autumn in the southern hemisphere.
In addition, the ESA explained that Titan’s atmosphere is dominated by nitrogen, and also contains small amounts of methane and other trace gases. Since the moon is roughly 10 times further away from the Sun than Earth, it is extremely cold, which allows methane and other hydrocarbons to rain onto the surface and form lakes and rivers.
Cassini first detected the swirling cloud in May 2012, when the southern hemisphere was experiencing autumn, NASA said. The cloud was several hundred miles across, and appeared to be an effect of the season change, the agency noted. However, scientists were puzzled by the altitude of the polar vortex – it is roughly 200 miles above Titan’s surface, and experts had believed that conditions there were too cold for clouds to form.
“We really didn’t expect to see such a massive cloud so high in the atmosphere,” Dr. de Kok said. To learn more about the cloud, the study authors poured over Cassini’s observations and discovered a key clue in the spectrum of sunlight reflected by the moon’s atmosphere.
“A spectrum splits the light from a celestial body into its constituent colors, revealing signatures of the elements and molecules present,” NASA explained. “Cassini’s visual and infrared mapping spectrometer (VIMS) maps the distribution of chemical compounds in Titan’s atmosphere and on its surface.”
Dr. de Kok explained that the light originating from the polar vortex was considerably different to other parts of Titan’s atmosphere, and noted that the researchers were able to clearly detect signs of frozen HCN molecules.
While HCN in gas form is present in small amounts in the moon’s atmosphere, the discovery of such molecules in the form of ice was surprising because HCN can only condense to form frozen particles if atmospheric temperatures reach levels of about minus 234 degrees Fahrenheit (minus 148 degrees Celsius) – about 200 degrees Fahrenheit (about 100 degrees Celsius) colder than theoretical models of Titan’s upper atmosphere currently predict.
To verify their results, the study authors looked at observations from Cassini’s composite infrared spectrometer (CIRS), which measures atmospheric temperature at different altitudes. That data revealed rapid cooling in Titan’s southern hemisphere, demonstrating that it would be possible to reach temperatures cold enough to cause the formation of the giant toxic cloud seen on the south pole.
“Atmospheric circulation has been drawing large masses of gas towards the south since the change of season in 2009,” NASA explained. “As HCN gas becomes more concentrated there, its molecules shine brightly at infrared wavelengths, cooling the surrounding air in the process. Another factor contributing to this cooling is the reduced exposure to sunlight in Titan’s southern hemisphere as winter approaches there.”
“These fascinating results from a body whose seasons are measured in years rather than months provide yet another example of the longevity of the remarkable Cassini spacecraft and its instruments,” added Earl Maize, Cassini project manager at the Jet Propulsion Laboratory (JPL) in Pasadena, California. “We look forward to further revelations as we approach summer solstice for the Saturn system in 2017.”