Cassini may have burned up in Saturn’s atmosphere almost a year ago, but the probe’s data sets are still transforming our understanding of Saturn and its various moons. In this visible spectrum, Saturn’s moon of Titan doesn’t look like much, mostly resembling a shapeless yellow ball, as shown above.
One of the tools aboard Cassini was the Visible and Infrared Mapping Spectrometer, or VIMS. It’s described on legacy pages as collecting “both light that is visible to humans and infrared light of slightly longer wavelengths. It separated the light into its various wavelengths so scientists could learn about the composition of materials from which the light is reflected or emitted.” In this case, VIMS made composite images of Titan that were later released by NASA in 2005 and 2006. One such composite shot is shown below:
So what’s changed between then and now? A great deal of effort has been put into combining a larger suite of composite shots and improving the composite itself. Because Titan is so difficult to image in the visible spectrum, the infrared camera inside the VIMS instrument was, well, instrumental in seeing the surface of the planet and taking these shots in the first place. The result, when you combine 13 years of cumulative data and fill in the gaps and less-imaged areas is nothing short of phenomenal:
Any full color image is comprised of three color channels: red, green and blue. Each of the three color channels combined to create these views was produced using a ratio between the brightness of Titan’s surface at two different wavelengths (1.59/1.27 microns [red], 2.03/1.27 microns [green] and 1.27/1.08 microns [blue]). This technique (called a “band-ratio” technique) reduces the prominence of seams, as well as emphasizing subtle spectral variations in the materials on Titan’s surface. For example, the moon’s equatorial dune fields appear a consistent brown color here. There are also bluish and purplish areas that may have different compositions from the other bright areas, and may be enriched in water ice.
Titan is thought to resemble Earth in its earliest days of evolution, albeit at a drastically colder temperature. It is the only known body in the solar system in which liquid precipitation is known to fall, though in Titan’s case, the “rain” isn’t water — it’s hydrocarbons. Life could theoretically exist on the moon — it has a hydrological cycle and many complex organic compounds in its atmosphere and on the surface. The temperature on Titan, however, is far lower than on Earth (average -90C) and the lack of surface water means that any life that did arise would either have to be based on a subsurface ocean (theorized to exist) or be based in alternative chemistries. It remains a candidate for life in our solar system, though possibly behind locations like Enceladus or Europa.