Improving the Usability of Galileo and Voyager Images of Jupiter's Moon Europa.

NASA's Voyager 1, Voyager 2, and Galileo spacecraft acquired hundreds of images of Jupiter's moon Europa. These images provide the only moderate‐ to high‐resolution views of the moon's surface and are therefore a critical resource for scientific analysis and future mission planning. Unfortunately, uncertain knowledge of the spacecraft's position and pointing during image acquisition resulted in significant errors in the location of the images on the surface. The result is that adjacent images are poorly aligned, with some images displaced by more than 100 km from their correct location. These errors severely degrade the usability of the Voyager and Galileo imaging data sets. To improve the usability of these data sets, we used the U.S. Geological Survey Integrated Software for Imagers and Spectrometers to build a nearly global image tie‐point network with more than 50,000 tie points and 135,000 image measurements on 481 Galileo and 221 Voyager images. A global least‐squares bundle adjustment of our final Europa tie‐point network calculated latitude, longitude, and radius values for each point by minimizing residuals globally, and resulted in root mean square (RMS) uncertainties of 246.6 m, 307.0 m, and 70.5 m in latitude, longitude, and radius, respectively. The total RMS uncertainty was 0.32 pixels. This work enables direct use of nearly the entire Galileo and Voyager image data sets for Europa. We are providing the community with updated NASA Navigation and Ancillary Information Facility Spacecraft, Planet, Instrument, C‐matrix (pointing), and Events kernels, mosaics of Galileo images acquired during each observation sequence, and individual processed and projected level 2 images. Plain Language Summary: Europa's subsurface ocean contains all the ingredients necessary for life, and this Jovian moon is therefore the target of continued scientific investigations and future exploration. Most of the pictures we have of Europa's surface were returned by the Voyager 1, Voyager 2, and Galileo spacecraft. These pictures provide insight into Europa's complex surface geology and ultimately clues to conditions within the ocean itself. Unfortunately, the pictures are hard to use because the location of the images on the surface are often incorrect. The result is that pictures that should overlap each other do not, or two apparently overlapping pictures show completely different scenes. In this work, we correct the locations of almost all the Galileo images and many of the Voyager images by identifying thousands of features that are in common between two or more images, and then mathematically calculating new locations for each feature such that the mismatch between pictures is globally minimized. We then created a set of mosaics that combine all the pictures taken during each Galileo flyby. We provide these mosaics, individual pictures, and improved camera pointing information to the community. Key Points: We improved the usability of 481 Galileo and 221 Voyager images of Europa by updating image locations on the surfaceNearly the entire Europa Galileo image set is now "analysis‐ready," requiring no additional image processingWe have publicly released Galileo observation sequence mosaics, individual projected images, and updated camera pointing kernels [ABSTRACT FROM AUTHOR]