MessageToEagle.com - A paper published this week using data from NASA's Cassini mission describes in more
detail than ever before how aerosols in the highest part of the atmosphere are kick-started at Saturn's moon Titan.
Scientists want to understand aerosol formation at Titan because it could help predict the behavior of smoggy
aerosol layers on Earth.
According to the new paper, published this week in the Proceedings of the National Academy of Sciences, Titan's
trademark reddish-brown smog appears to begin with solar radiation on molecules of nitrogen and methane in the
ionosphere, which creates a soup of negative and positive ions.
Click on image to enlarge>
Reflection of Sunlight off Titan Lake
This image shows the first flash of sunlight reflected off a lake on Saturn's moon Titan. The glint off a mirror-like
surface is known as a specular reflection. This kind of glint was detected by the visual and infrared mapping spectrometer
(VIMS) on NASA's Cassini spacecraft on July 8, 2009. It confirmed the presence of liquid in the moon's northern hemisphere,
where lakes are more numerous and larger than those in the southern hemisphere. Scientists using VIMS had confirmed the p
resence of liquid in Ontario Lacus, the largest lake in the southern hemisphere, in 2008. Credits: NASA/JPL/University of Arizona/DLR
Collisions among the organic molecules and the
ions help the molecules grow into bigger and more complex aerosols. Lower down in the atmosphere, these aerosols
bump into each other and coagulate, and at the same time interact with other, neutral particles.
Eventually, they form the heart of the physical processes that rain hydrocarbons on Titan's surface and form
lakes, channels and dunes.
The paper was led by Panayotis Lavvas, a Cassini participating scientist based at the University of Reims,
Champagne-Ardenne, France. The team analyzed data from three Cassini instruments -- the plasma spectrometer,
the ion and neutral mass spectrometer, and the radio and plasma wave science experiment.
They compared their results to those obtained by ESA's Huygens probe on its descent through the Titan
atmosphere in 2005 and found they were compatible.
The northern hemisphere - (image above) - was shrouded in darkness for nearly 15 years, but the sun began to
illuminate the area again as it approached its spring equinox in August 2009. VIMS was able to detect the glint as the
viewing geometry changed.
Titan's hazy atmosphere also scatters and absorbs many wavelengths of light, including most
of the visible light spectrum. But the VIMS instrument enabled scientists to look for the glint in infrared wavelengths
that were able to penetrate through the moon's atmosphere. This image was created using wavelengths of light in the 5 micron range.
By comparing the new image to radar and near-infrared light images acquired from 2006 to 2008, Cassini scientists
were able to correlate the reflection to the southern shoreline of a Titan lake called Kraken Mare.
The sprawling Kraken Mare covers about 400,000 square kilometers (150,000 square miles). The reflection appeared to come
from a part of the lake around 71 degrees north latitude and 337 degrees west latitude.
It was taken on Cassini's 59th flyby of Titan on July 8, 2009, at a distance of about 200,000 kilometers (120,000 miles).
The image resolution was about 100 kilometers (60 miles) per pixel. Image processing was done at the German Aerospace
Center in Berlin and the University of Arizona in Tucson.