A global infrared mosaic of Saturn’s moon Enceladus created using a complete dataset from the Cassini spacecraft has revealed new detail on the moon’s surface.
Cassini orbited Saturn and its moons from 2004 to 2017. The mission ended when the spacecraft was intentionally plunged into the planet’s atmosphere, but new discoveries are still being made with the data.
During the mission lifetime, Cassini flew by Enceladus 147 times, with 23 close encounters of the icy moon. The Visual and Infrared Mapping Spectrometer (VIMS) collected data that can be used to reveal information on the temperature and composition of the surface, as well as the sizes and crystallinity of ice grains.
A study published in Icarus has produced a global spectral mosaic using the complete VIMS dataset. The full-color images were created by combining three IR channels of the VIMS spectro-imager, represented here by red, green, and blue colors, and overlapping these on a mosaic created using the Imaging Science Subsystem on Cassini by another team.
The image shows five infrared views of Enceladus centered on the leading side, the Saturn-facing side, and the trailing side in the top row, and the North and South Pole in the bottom row. The globe can also be explored interactively:
Infrared images of Enceladus were used to make this interactive 3D globe. Image Credit: NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science Institute
The scientists used a photometric correction to reveal new details on the surface of the moon. Enceladus has a surface composed almost of pure water ice, which makes it highly reflective, but the observed brightness depends on the properties of the surface material, the surface shape, and the angle at which it is viewed. Correcting for these variations was necessary to show the differences in composition and physical state at the surface.
By using these improved photometric corrections, the scientists have been able to reveal spectral variations which correspond to the different colours in the images. These are particularly striking in the region with four large tectonic faults known as the Tiger Stripes at the South Pole. The image of the South Pole also reveals a clear boundary between terrains where the light red colour meets the blue region. The smooth red colour seen in the first image is likely due to recently exposed freshwater ice. This could be the surface signature of hotspots on the seafloor.
In the future the scientists plan to apply their technique to other icy moons to compare them with Enceladus. Similar infrared mapping by the Juice and Europa Clipper missions will be able to detect recent activity on Jupiter’s moons Europa and Ganymede.
For more on this study, read Infrared Eyes on Enceladus: Hints of Fresh Ice in Northern Hemisphere of Saturn’s Moon.
Reference: “Photometrically-corrected global infrared mosaics of Enceladus: New implications for its spectral diversity and geological activity” by R. Robidel, S. Le Mouélic, G. Tobie, M. Massé, B. Seignovert, C. Sotin and S. Rodriguez, 23 May 2020, Icarus.
The Cassini mission is a cooperative project between NASA, ESA, and Italy’s ASI space agency.