Titanic Purple Haze

Titan’s hazy atmosphere. Image Credit: NASA/JPL

Encircled in purple stratospheric haze, Titan appears as a softly glowing sphere in this colorized image taken one day after Cassini’s first flyby of that moon.

This image shows two thin haze layers. The outer haze layer is detached and appears to float high in the atmosphere. Because of its thinness, the high haze layer is best seen at the moon’s limb.

The image was taken using a spectral filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The image has been falsely colored: The globe of Titan retains the pale orange hue our eyes usually see, and both the main atmospheric haze and the thin detached layer have been brightened and given a purple color to enhance their visibility.

The best possible observations of the detached layer are made in ultraviolet light because the small haze particles which populate this part of Titan’s upper atmosphere scatter short wavelengths more efficiently than longer visible or infrared wavelengths.

Images like this one reveal some of the key steps in the formation and evolution of Titan’s haze. The process is thought to begin in the high atmosphere, at altitudes above 400 kilometers (250 miles), where ultraviolet light breaks down methane and nitrogen molecules. The products are believed to react to form more complex organic molecules containing carbon, hydrogen and nitrogen that can combine to form the very small particles seen as haze. The bottom of the detached haze layer is a few hundred kilometers above the surface and is about 120 kilometers (75 miles) thick.

The image was taken with the narrow angle camera on July 3, 2004, from a distance of about 789,000 kilometers (491,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 114 degrees. The image scale is 4.7 kilometers (2.9 miles) per pixel.

The superimposed coordinate system grid in the accompanying image at right illustrates the geographical regions of the moon that are illuminated and visible, as well as the orientation of Titan — lines of longitude converge on the South Pole near the moon’s eastern limb. The yellow curve marks the position of the boundary between day and night on Titan.

The haze of an atmospheric layer on Saturn’s moon, Titan. With an atmosphere thicker than Earth’s, and composed of many biochemically interesting molecules (methane, hydrogen and carbon), Titan’s rich chemistry will continue to interest astrobiologists as they look forward to landing a probe on its surface in 2004-5. Credit: Voyager Project, JPL, NASA

Titan will get the lion’s share of Cassini’s attention: 45 close flybys are planned for the giant moon. Titan will also be the target of the Huygens probe, which will be released by Cassini on Christmas day (Christmas eve in the U.S.) for descent through Titan’s atmosphere 3 weeks later. Titan is of particular interest to scientists because, like Earth, it has an atmosphere that contains nitrogen and organic molecules such as methane. Some scientists speculate that Titan’s chemistry may offer a snapshot of what Earth’s chemistry was like before life took hold.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

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