A global infrared mosaic from Saturn̵
Cassini orbited Saturn and its moons from 2004 to 2017. The mission ended when the spacecraft was purposely submerged in the planet’s atmosphere, but new discoveries are still being made with the data.
During the missionary life, Cassini flew past Enceladus 147 times, with 23 encounters with the icy moon. The visual and infrared mapping spectrometer (VIMS) collected data that can provide information about the temperature and composition of the surface, as well as the size and crystallinity of ice grains.
A study published in Icarus created a global spectral mosaic using the full 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 them on a mosaic created by another team with the Imaging Science Subsystem on Cassini has been.
The image shows five infrared views of Enceladus centered on the front, Saturn-facing side, and back side in the top row, and the north and south poles in the bottom row. The globe can also be explored interactively:
Infrared images from Enceladus were used to create this 3D interactive globe. Credit: NASA/.JPL-Caltech / University of Arizona / LPG / CNRS / University of Nantes / Space Science Institute
The scientists used photometric correction to reveal new details on the lunar surface. Enceladus has a surface that is almost pure water ice, which makes it highly reflective. However, the observed brightness depends on the properties of the surface material, the surface shape and the viewing angle. Correcting these variations was necessary to reveal the differences in composition and physical state on the surface.
Using these improved photometric corrections, the scientists were able to uncover spectral variations that correspond to the different colors in the images. These are particularly noticeable in the region with four major tectonic faults known as the tiger stripes at the South Pole. The image of the South Pole also shows a clear boundary between the areas where the bright red color meets the blue region. The smooth red color in the first picture is likely due to recently exposed freshwater ice. This could be the surface signature of hotspots on the ocean floor.
In the future, the scientists plan to apply their technique to other icy moons in order to compare them with Enceladus. Similar infrared mapping by the Juice and Europa Clipper missions will be able to spot recent activity on JupiterMoons Europa and Ganymede.
For more information on this study, see Infrared Eyes on Enceladus: Evidence of Fresh Ice in the Northern Hemisphere of Saturn’s Moon.
Reference: “Photometrically Corrected Global Infrared Mosaics by 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, May 23, 2020, Icarus.
DOI: 10.1016 / j.icarus.2020.113848
The Cassini mission is a collaborative project between NASA, ESA and the Italian space agency ASI.