Equipotential Shape Models for the Gas Giants README FILE Dustin Buccino May 5, 2020 Jet Propulsion Laboratory California Institute of Technology ============================================================================= INTRODUCTION ============================================================================= This dataset contains geopotential shape models of Jupiter and Saturn derived from the high-precision gravitational field models produced by the Juno mission to Jupiter and Cassini's Grand Finale at Saturn. This dataset is intended to be paired with the following article submitted to the Journal of Geophysical Research-Planets: Buccino, Dustin R., Ravit Helled, Marzia Parisi, William Hubbard, and William Folkner, "Updated Geopotential Shapes of Jupiter and Saturn using Juno and Cassini Grand Finale Gravity Science Measurements", Journal of Geophysical Research, 2020 (submitted Jan 2020). This dataset of shape models was produced in part at the Jet Propulsion Laboratory by the Juno Gravity Instrument Team and Interiors Working Group. ============================================================================= ARCHIVE INFORMATION ============================================================================= This archive contains a total of four data products in two formats. A single geopotential shape model is provided in both an ASCII plain-text format and NAIF-compatible Binary Digital Shape (DSK) kernel of the shape is provided for each planet. All shape models are azimuthally-symmetric. The following describes these data files in more details: Jupiter Geopotential Shape Model ------------------------------------------------------------------------- BDS_FILENAME = jupiter-juno-iess2018-1bar-equipotential.bds TXT_FILENAME = jupiter-juno-iess2018-1bar-equipotential.txt This shape model of Jupiter was derived from measurements of Jupiter's gravitational field coefficients with the Juno spacecraft (Iess et al, 2018). This shape model accounts for zonal gravitational coefficients J2 through J10 and the centrifugal potential with a nominal spin rate of T = 9h 55m 29.7s (Lindal, 1992). Dynamical heights are applied to the final column using the Zonal wind profile from the Cassini Flyby (Porco et al, 2003). This shape model uses a polar reference radius of B = 66,864 km, corresponding with the estimated 1 bar level of Jupiter's atmosphere. This version is at a resolution of 0.5 degree steps. Saturn Geopotential Shape Model ------------------------------------------------------------------------- BDS_FILENAME = saturn-cassini-iess2019-1bar-equipotential.bds TXT_FILENAME = saturn-cassini-iess2019-1bar-equipotential.txt This shape model of Saturn derived from measurements of Saturn's gravitational field coefficients with the Cassini spacecraft during the Grand Finale (Iess et al, 2019). This shape model accounts for zonal gravitational coefficients J2 through J10 and the centrifugal potential with a spin rate of T = 10h 33m 38s (Mankovich et al, 2019), which is the spin rate estimated from ring seismology. Dynamical heights are applied to the final column using the Zonal wind profile ISS2004-2008 (Garcia-Melendo et al, 2011). This shape model uses a polar reference radius of B = 54,364 km, corresponding with the estimated 1 bar level of Saturn's atmosphere. This version is at a resolution of 0.5 degree steps. ============================================================================= FILE FORMAT ============================================================================= This dataset contains two separate file formats as described above. ASCII plain-text files are given with the "*.txt" extension and the binary digital shape kernels are given with the "*.bds" extension. TXT FILES ------------------------------------------------------------------------- The ASCII plain-text files are human-readable, comma-separated text files. The first column represents the geocentric latitude in units of degrees. The second column represents the ellipsoidal shape in units of kilometers. The third column represents the geopotential shape in units of kilometers. The fourth column represents the isobaric shape where the geopotential has been adjusted to account for the dynamic heights caused by the winds with the preferred wind model. The fifth, sixth, and seventh column are the dynamical heights only from individual wind models BDS FILES ------------------------------------------------------------------------- Binary Digital Shape kernels (file extension: BDS) are a binary file format which allow for arbitrary (i.e. non-ellipsoidal) shape models to be used within the SPICE system. In order to read the BDS files in this dataset, one should refer to the section below in order to acquire the software to read them. The BDS files in this dataset contain *only* the isobaric shape, i.e. the geopotential adjusted for the dynamical heights. Although the units are built-into the SPICE system, they are defined in units of degrees and kilometers. To interface with Digital Shape Kernels, the SPICE interface is required. SPICE and the DSK interface can be found online at: https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/dsk.html ============================================================================= FIGURE REPRODUCTION ============================================================================= This section will describe the data that are used to produce the figures in the article that describes this dataset. FIGURE 1 ------------------------------------------------------------------------- Figure 1 is produced using the following columns from the plain-text files: - Latitude (Column 1) - Ellipsoid Shape - yellow dash curve (Column 2) - Geopotential Shape - orange curve (Column 3) - Geopotential Shape with Dynamical Height - blue curve (Column 5) Full reproduction requires the subtraction of the individual columns to produce the subplots. FIGURE 2 ------------------------------------------------------------------------- Figure 2 is produced using the following columns from the plain-text files: - Latitude (Column 1) - Dynamical Heights (Columns 5, 6, & 7) FIGURE 3 ------------------------------------------------------------------------- Figure 2 is produced using the following columns from the plain-text files: - Latitude (Column 1) - Surface Gravity (Columns 8) ============================================================================= ACKNOWLEDGMENTS ============================================================================= This work was partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Government sponsorship acknowledged. Co-author Ravit Helled acknowledges support from SNSF grant 200020_188460. Finally, we thank the Juno science team members for valuable discussions. ============================================================================= PRIMARY POINT OF CONTACT ============================================================================= Dustin Buccino Jet Propulsion Laboratory Planetary Radar and Radio Sciences (818) 393 - 1072 Dustin.R.Buccino@jpl.nasa.gov ============================================================================= ACRONYMS AND ABBREVIATIONS ============================================================================= ASCII American Standard Code for Information Interchange BDS Binary Digital Shape (file extension for DSK files) DOY Day of year DSK Digital Shape Kernel DSN Deep Space Network JPL Jet Propulsion Laboratory NAIF Navigation Ancillary Information Facility NASA National Aeronautics and Space Administration PDS Planetary Data System RS Radio Science RSS Radio Science Subsystem SIS Software Interface Specification TXT Text file