NASA has published a series of 6 images of Titan, one of the moons of the planet Saturn, seen at infraredd by the Cassini space probe’s VIMS instrument. The images were created by combining observations conducted over the 13 years of the mission that were processed to compensate for the fact that they were made with a great variety of light conditions and viewing angle by Cassini.
The mission of the Cassini space probe ended on September 15, 2017, but the scientists who study Saturn and/or its moons in one way or another keep on analyzing and processing them. Titan was one of the most important targets for study since the beginning of the mission because there were already clues that it had similarities with the primordial Earth, even if it’s much colder, and active from the chemical point of view. For this reason, over the course of 13 years many observations of this moon were conducted and increasingly precise maps of its surface were created based on the data collected by different instruments on board the probe.
The VIMS (Visual and Infrared Mapping Spectrometer) instrument allowed the Cassini space probe to actually see Titan’s surface thanks to the fact that the atmosphere of that moon absorbs only a small part of the infrared frequencies it can detect. Instead, the aerosols present in the upper layers of Titan’s atmosphere cause a noticeable scattering of visible frequencies with the consequence that the result obtained by a camera of Cassini’s Imagination Science Subsystem (ISS) is Titan appears as in the photo at the center of the image.
A problem in examining the maps created is due to the fact that during the many Titan flybys carried out by the Cassini space probe the brightness was different, the observations were made from different angles and the weather conditions were also different. The consequence is that some maps are mosaics made up of various images in which we can see the boundaries and make them homogeneous is difficult.
A complex processing technique based on the fact that all color images are composed of three channels for the red, green and blue colors allowed to reduce the boundaries between the various images and to emphasize subtle spectral variations in the materials on Titan’s surface. For example, now the dunes at this moon’s equator appear consistently brown. Some bluish and purplish areas may have compositions different from other bright areas and can be rich in water ice.
NASA presented maps of Titan that showed various elaborations needed to make them homogeneous at the end of March 2016. Meanwhile, the Cassini space probe collected more data and the processing techniques were refined. A new mission was proposed to send a new space probe to the Saturn system with an infrared instrument improved compared to VIMS thanks to the experience gained. Even if it’s approved, it will still take several years to collect new data from near Titan.