Our group is jointly involved in the development and operation of the JAXA Asteroid Data Explorer (JADE) web-based Ryugu image data searching system for Hayabusa2’s Optical Navigation Camera (ONC).

JADE: https://jade.darts.isas.jaxa.jp

An explanation of JADE is here.

We have made Ryugu background maps (base maps) used in JADE available for download on this page.

1. High-resolution mosaic map

[Explanation]

The background image is made from low-resolution (2 m) ONC v-band (550 nm wavelength) images, observed from high altitude (20 km). (Research paper Sugita et al. 2019)

The overlay is amosaic made from ONC images (medium-altitude operations, 0.5 m resolution) observed by the explorer at altitude of 5 km. Since the observed range is limited to low-latitude areas, high-latitude areas are in low resolution.

Projection: Equirectangular projection　（Equirectangular projection, Simple cylindrical projection）

2. False coloration map

[Explanation]

Facing opposite the sun offers conditions to capture images of Ryugu with no shadows, similar to a full moon. Reflectance observed under these conditions is called normal albedo. Since this image is not susceptible to being affected by rugged terrain, it is ideal for investigating surface coloration. (Research paper Yokota et al. 2021)

Separate observation bands have been allocated to each of the RGB color channels. Since the wavelengths are not the same as those visible to the human eye, we produce it as false coloration.

Blue channel -> 480 nm wavelength
Green channel -> 549 nm wavelength
Red channel -> 857 nm wavelength

Ryugu should appear black and colorless (no difference at any wavelength) when seen with the human eye, but we have accentuated it here to make the subtle differences easier to distinguish.

3. Spectral slope map

[Explanation]

Ryugu is a celestial body without many color characteristics, but at visible and near-infrared light wavelength regions the slope of its plot differs by region in the graph indicating the relationship between wavelength and reflectance (reflectance spectra graph). This fact has been reported in multiple papers.

This map recreated values for spectral slope from normal albedo data in “2.” above, as was done in research paper Kameda et al (2021).

Red indicates relatively higher reflectance at long wavelengths, while blue indicates the opposite.

Reference:

• Sugita et al. (2019). The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes, Science 364, 6437.
  https://doi.org/10.1126/science.aaw0422
• Yokota et al. (2021). Opposition Observations of 162173 Ryugu: Normal Albedo Map Highlights Variations in Regolith Characteristics, Planet. Sci. J. 2 177.
  https://doi.org/10.3847/PSJ/ac14ba
• Kameda et al. (2021). Improved method of hydrous mineral detection by latitudinal distribution of 0.7-μm surface reflectance absorption on the asteroid Ryugu, Icarus 360, 114348.
  https://doi.org/10.1016/j.icarus.2021.114348