A quartet of false-color, composite images show the dance of Saturn's southern lights in data obtained by NASA's Cassini spacecraft. This image is among the first images to be released from a study that extracts auroral emissions out of the entire catalogue of images taken by Cassini's visual and infrared mapping spectrometer.
In this image constructed from data collected in the near-infrared wavelengths of light, the auroral emission is shown in green. The data represents emissions from hydrogen ions in of light between 3 and 4 microns in wavelength. In general, scientists designated blue to indicate sunlight reflected at a wavelength of 2 microns, green to indicate sunlight reflected at 3 microns and red to indicate thermal emission at 5 microns. Saturn's rings reflect sunlight at 2 microns, but not at 3 and 5 microns, so they appear deep blue. Saturn's high altitude haze reflects sunlight at both 2 and 3 microns, but not at 5 microns, and so it appears green to blue-green. The heat emission from the interior of Saturn is only seen at 5 microns wavelength in the spectrometer data, and thus appears red. The dark spots and banded features in the image are clouds and small storms that outline the deeper weather systems and circulation patterns of the planet. They are illuminated from underneath by Saturn's thermal emission, and thus appear in silhouette.
The images that make up the composite were obtained on May 24, 2007.