Photometric behavior of the Ryugu's spectral parameters retrieved from NIRS3 spectra

Kurzfassung

The JAXA/Hayabusa2 mission observed the Ryugu asteroid for one year and half and acquired images by means of the ONC camera and NIR spectra in the 1.8-3.6 microns range thanks to the NIRS3 spectrometer. Ryugu is a very dark body (albedo of 0.043, Sugita et al., 2019) and its NIR spectrum is characterized by the shallow 2.72 and 2.8 microns absorption bands, ascribed to OH stretiching and thus indicating a weak hydration (Kitazato et al., 2019). Photometric properties are very useful to infer optical and physical properties of the surface. The Ryugu photometry in the visible range has been studied by Tatsumi et al. (2020), which retrieved the average geometric albedo and the visible phase reddening. Pilorget et al. (2020) studied the NIR photometry observing a local anti-correlation between albedo and band depth. In this work, we focus on the photometric behavior of the main spectral parameters, describing the Ryugu’s NIR spectrum, i.e., infrared reflectance, albedo and spectral slope.