Shape models, their derivatives, and relating data and tools of the asteroid Ryugu used in the paper "Hayabusa2 observations of the top-shape carbonaceous asteroid 162173 Ryugu" by Watanabe et al. (2019).

Summary

This archive contains shape models and their derivatives of the asteroid Ryugu, together with tools, or pointers to tools used to produce the data. This archive prepared to reproduce the results presented in the paper "Hayabusa2 observations of the top-shape carbonaceous asteroid 162173 Ryugu" by Watanabe et al. (2019). It is provided "as is" without warranty of any kind, either express or implied.

Shape models

• SHAPE_SFM_3M_v20180804.obj
• SHAPE_SFM_800k_v20180804.obj
• SHAPE_SFM_200k_v20180804.obj
• SHAPE_SFM_49k_v20180804.obj
• SHAPE_SFM_49k_v20180804.dat

The 3M polygon model (SHAPE_SFM_3M_v20180804.obj) is the initial output of our shape modeling procedure, and the 800k, 200k and 49k polygon models are reduced version. They are stored in in the Wavefront OBJ format. SHAPE_SFM_49k_v20180804.dat is the model identical to the 49k model (SHAPE_SFM_49k_v20180804.obj), but converted to use our gravitational analysis with GFandSlope.

Derivatives from the shape models

• Gravity_SHAPE_SFM_49k_v20180804_7.63_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_4.00_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_3.90_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_3.80_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_3.70_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_3.60_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_3.50_1200a.txt
• Gravity_SHAPE_SFM_49k_v20180804_3.40_1200a.txt

Gravity_SHAPE_SFM_49k_v20180804_XXXX_1200a.txt, where XXXX is the rotation period. The file contains an ASCII table of gravity potential, slope and other auxiliary values computed by GFandSlope (see below) for every polygon plate of the 49k polygon shape model at a given rotation period and with an assumed uniform density of 1200 kg/m^3.

• PlateID - ID of polygon plate.
• center_xyz – Coordinates of the center of the polygon plate in the asteroid body-fixed frame, expressed in km. All following values are computed at this point.
• lon/lat – Longitude and Latitude of the polygon plate center.
• CRefAccxyz – XYZ components of the centrifugal acceleration at the given rotation period, expressed in the SI unit.
• attract_xyz – XYZ components of the net gravitational acceleration (sum of the pure gravitational acceleration and the centrifugal acceleration), expressed in the SI unit.
• Gpotential - Geopotential without the centrifugal force, expressed in the SI unit.
• Rpotential - Potential of the centrifugal force at the given rotation period, expressed in the SI unit.
• Tpotential - Total potential of the geopotential and the rotational potential, expressed in the SI unit.
• GeopotentialSlope - Slope at the polygon plate center computed from the net gravitational acceleration vector and the normal vector, expressed in degrees.
• normal_xyz - Normal vector pointing the outward of the surface at the polygon plate center.
• area - Area of the polygon plate , expressed in km^3.

• Diff_SFM0804-SPC0829.txt

Differences in topography between the SfM model and the SPC model computed for every polygon plate of the 3M polygon model appeared in Fig. S2. Expressed in km.

• SHAPE_SFM_3M_v20180804.csv

List of informations (polygon center coordinate, area, latitude and longitude, and radius from the origin, see the 1st line of the file for detail) of every polygon plates consisting the 3M shape model. It was used analysis on surface tilt angles. See below and README_TiltAngleAnalysis.docx for detailed usage of the file.

ONC images

• Watanabe_2019_ONC.zip

ONC images and related files used in Fig. 1 and 4A. See README_Fig4.docx for detailed description of Fig. 4A. General description of the ONC data is found at http://darts.isas.jaxa.jp/planet/project/hayabusa2/

Tools

Package Tools (Not included in this archive)

• Agisoft PhotoScan 1.4

Agisoft PhotoScan was used to produce the SfM shape models. It is a commercial software by Agisoft, available at the Agisoft website (https://www.agisoft.com). PhotoScan currently renamed to Agisoft MetaShape 1.5.

• Stereophotoclinometry (SPC)

The SPC code was used to produce SPC shape models. It is developed and maintained by R. Gaskell and Planetary Science Institute. Distribution of the SPC software is legally restricted by the US International Traffic in Arms Regulation. US citizens (only) may request an SPC research licence, with appropriate restrictions, at http://spc.psi.edu .

• GMT

GMT (Generic Mapping Tools) is used to produce Fig. S4 from outputs of GFandSlope. GMT is available at the project site (http://gmt.soest.hawaii.edu/projects/gmt).

• AiGIS

AiGIS is a visualization tool for small body exploration data developed by the University of Aizu, available at the developer’s website (https://arcspace.jp/aigis/). It was used to produce pictures appeared in Figs. 2, 3B, and S2.

Script and tools internally developed by the authors

• GFandSlope.cpp

C++ tool to compute gravitational potential and slope of the asteroid surface with the given rotational period and density.

How to Compile

$ g++ GFandSlope.cpp

Attached header files (GF.h and vector3.h by S. Zenitani, 2001) should be placed at the same directory. Also it requires the SPICE toolkit developed and distributed by NAIFJPLNASA (https://naif.jpl.nasa.gov/naif/). Usage

$ GFandSlope SHAPEMODEL.dat ROTATION_PERIOD DENSITY

It will work by giving a shape model, rotation period (expressed in Hours), and density (expressed in the SI unit) as arguments.

• Slope_Statistics_Watanabe+2019.ipynb

Jupyter Notebook script to compute and plot statistical information of the slope and gravitational potential that calculated by GFandSlope. It was used to produce plots appeared in Fig. 2A and S5.

• WS2019_SM_tilt.R

R script to compute surface tilt angles in Fig. S3. See README_TiltAngleAnalysis.docx for details.

• ShapeAnalyses.txt

ImageJ script to compute equatorial aspect ratio and the circularity of asteroid bodies in SM7 and Table S3. See README_ShapeAnalyses.docx for details.

• Files for the FEM analyses

The input files to ANSYS Mechanical APDL are available at

Auburn University ( http://hdl.handle.net/11200/49368 ).

• Files for safety index map

A tool to produce the safety index map in Fig. S7 is packaged in safety_index maps_source_codes.zip. It requires a shape model in the STL format. The STL format shape model can be obtained by converting from the OBJ format shape models with MeshLab or other major shape model handling tools. See How_to_generate_safety_index maps.pdf for details of the tool.

Note

This document was prepererd by Naru Hirata, the University of Aizu (naru@u-aizu.ac.jp) on Mar. 4, 2019.