Geodesy and cartography methods of exploration of the outer planetary systems: Galilean satellites and Enceladus

Abstract

While Galilean satellites have been observed by different spacecrafts, including Pioneer, Voyager-1 and -2, Galileo, New Horizons, and Enceladus by Cassini and Voyager-2, only data from Galileo, Cassini and the two Voyagers are useful for precise mapping. For purposes of future missions to the system of outer planets we have re-computed the control point network of the Io, Ganymede and Enceladus to support spacecraft navigation and coordinate knowledge. Based on the control networks, we have produced global image mosaics and maps. Geodesy approach. For future mission Laplace-P we mainly focused on Ganymede which coverage is nearly complete except for polar areas (which includes multispectral data). However, large differences exist in data resolutions (minimum global resolution: 30 km/pixel). Only few areas enjoy coverage by highest resolution images, so we suggest to obtain regional Digital Elevation Models (DEMs) from stereo images for selected areas. Also using our special software, we provide calculation of illumination conditions of Ganymede surface in various representations. Finally, we propose a careful evaluation of all available data from the previous Voyager and Galileo missions to re-determine geodetic control and rotation model for other Galilean satellites - Callisto and Europe. Mapping. Based on re-calculated control point networks and global mosaics we have prepared new maps for Io, Ganymede and Enceladus. Due to the difference in resolution between the images, which were also taken from different angles relative to the surface, we can prepare only regional high resolution shape models, so for demonstrating of topography and mapping of the satellites we used orthographic projection with different parameters. Our maps, which include roughness calculations based on our GIS technologies, will also be an important tool for studies of surface morphology. Conclusions. Updated data collection, including new calculation of elements of external orientation, provides new image processing of previous missions to outer planetary system. Using Photomod software (http://www.racurs.ru/) we have generated a new control point network in 3-D and orthomosaics for Io, Ganymede and Enceladus. Based on improved orbit data for Galileo we have used larger numbers of images than were available before, resulting in a more rigid network for Ganymede. The obtained results will be used for further processing and improvement of the various parameters: body shape parameters and shape modeling, libration, as well as for studying of the surface interesting geomorphological phenomena, for example, distribution of bright and dark surface materials on Ganymede and their correlations with topography and slopes.