Cassini VIMS sees the long-awaited glint off a Titan lake
The Planetary Society Blog - 17 Dec 2009
The Cassini mission announced today the first observation of a specular reflection off of a lake on Titan. A specular reflection is a mirror-like flash, and you only get one when you have a mirror-like surface -- very, very smooth. That's hard to do in nature except with a liquid surface (or a surface that froze from a liquid, such as ice and certain types of lava flows). I'll summarize the long road to the specular reflection below, but first, here's the image, certain to become an iconic one of Titan.
Specular reflection off of a Titan lake
(NASA/JPL/University of Arizona/DLR)
On July 8, 2009, Cassini finally saw the telltale glint of sunlight specularly reflecting off of the mirror-like
surface of a lake on northern Titan. This image is from the VIMS instrument employing infrared light at a
wavelength of 5 microns, and has been colorized to match visible-light pictures of Titan.
PIA12481: Reflection of Sunlight off Titan Lake
NASA JPL Cassini - 17 Dec 2009
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 presence of liquid in Ontario Lacus, the largest lake in the southern hemisphere, in 2008.
The northern hemisphere 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.