An evaluation method of reflectance spectra to be obtained by Hayabusa2 Near-Infrared Spectrometer (NIRS3) based on laboratory measurements of carbonaceous chondrites

Abstract

We conducted ground-based performance evaluation tests of the Near-Infrared Spectrometer (NIRS3) onboard Hayabusa2 spacecraft in November 2013 and from April to May 2014 and established a method for evaluating its measured reflectance spectra. Reflectance spectra of nine powdered carbonaceous chondrite samples were measured by both NIRS3 and a Fourier transform infrared (FT-IR) spectrometer. We have established two methods for correcting the NIRS3 data by comparing them with the corresponding FT-IR data because raw data obtained by NIRS3 underwent spectral distortion caused by systematic offsets in sensitivity of individual pixels. The corrected NIRS3 spectra of carbonaceous chondrite samples are comparable with their FT-IR spectra. The depth of each band component D λ is defined for each wavelength λ (μm) to characterize the absorption bands in NIRS3 spectra. It is suggested that the relationship between the D 2.72 /D 2.79 ratio and the D 2.76 /D 2.90 ratio would be useful for estimating the degree of heating of the asteroid surface, if contributions of terrestrial adsorbed water on D 2.79 and D 2.90 are properly corrected. The degrees of heating and space weathering are also comprehensively evaluated by the relationship between D 2.90 and the D 2.76 /D 2.90 ratio. Reflectance spectra of asteroid Ryugu, the target asteroid of Hayabusa2, to be recorded by the NIRS3 instrument are expected to reveal the characteristics of the surface materials by using the evaluation technique proposed in this paper. Such information will be used for choosing the touchdown points for sampling and also for investigating the distribution of the materials similar to the returned samples on Ryugu.

The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes

“…Individual meteorite names are indicated in the figure. The spectrum of powder (≤ 155 µm) sample of Jbilet Winselwan was measured at (30°, 0°, 30°) with the spectrometer system at Tohoku University(57). The rest of meteorite spectra are from(58).…”

“…Contours indicate 95% and 68% of the surface area. (B) Comparison in principal-component scores (PC2-PC3) with main-belt C-complex asteroids (56) (colored circles), a moderately dehydrated carbonaceous chondrite (Y 86029, orange diamond (58)), Murchison (CM2) samples with heating (black line (58)) and laser-irradiation (light green(57) and grey lines (58)) experiments, and heated Ivuna (CI) samples (blue line(58)). Parent bodies of major asteroid families in the inner main belt, Polana (blue star), Eulalia (red star), and Erigone (green star), for are also shown(56).…”

Assessing the debris generated by the small carry-on impactor operated from the <i>Hayabusa2</i> mission

“…The measured surface area of both samples were 2 mm × 5 mm in size. Detailed measurement conditions were published in Matsuoka et al (2017).…”