Follow-up observations for the Asteroid Catalog using AKARI Spectroscopic Observations

Abstract

In the 1-2.5 µm range, spectroscopic observations are made on the AcuA-spec asteroids, whose spectra were obtained in a continuous covered mode between 2.5-5.0 µm by AKARI.Based on the Bus-DeMeo taxonomy (DeMeo et al. 2009, Icarus, 202, 160), all the AcuA-spec asteroids are classified, using the published and our observational data. Additionally, taking advantage of the Bus-DeMeo taxonomy characteristics, we constrain the characteristic each spectral type by combining the taxonomy results with the other physical observational data from colorimetry, polarimetry, radar, and radiometry. As a result, it is suggested that certain C-, Cb-, B-type, dark X-, and D-complex asteroids have spectral properties compatible with those of anhydrous interplanetary dust particles with tiny bright material, such as water ice.This supports the proposal regarding the C-complex asteroids (Vernazza et al. 2015, ApJ, 806, 204; 2017, AJ, 153, 72). A combination of the Bus-DeMeo taxonomy for AcuA-spec asteroids and the presumptions with other physical clues such as the polarimetric inversion angle, radar albedo, and mid-infrared spectroscopic spectra will be beneficial for surface material constraints, from the AcuA-spec asteroid observations. 2

Distant Formation and Differentiation of Outer Main Belt Asteroids and Carbonaceous Chondrite Parent Bodies

“…We also ruled out brucite as a major cause of the 3.1 μm absorptions on the main belt asteroids observed using AKARI. AKARI spectra combined with ground‐based observation data (Hasegawa et al., 2017) did not show the 2.45 μm absorption (Figure S7 in Supporting Information ), which suggested the absence of brucite. The AKARI data thus indicate more Ceres‐like, ammonium phyllosilicate‐bearing asteroids than previously identified (Rivkin et al., 2019; Takir & Emery, 2012), increasing the need to explain the origin of ammonium, as NH 3 ice is unstable at those distances in the present Solar System.…”

Distant formation and differentiation of outer main belt asteroids and carbonaceous chondrite parent bodies

“…We also ruled out brucite as a major cause of the 3.1 µm absorptions on the main belt asteroids observed using AKARI. AKARI spectra combined with ground-based observation data (Hasegawa et al, 2017) did not show the 2.45 µm absorption (Supplementary Figure 7), which suggested the absence of brucite. The AKARI data thus indicate more Ceres-like, ammonium phyllosilicate-bearing asteroids than previously identified (Takir & Emery, 2012;Rivkin et al, 2019), increasing the need to explain the origin of ammonium, as NH 3 ice is unstable at those distances in the present Solar System.…”

“…We excluded the samples with unreliable spectra at any of the absorption bands we are interested in, following the criteria set by Usui et al (2019) (the uncertainty in the reflectance to be < 10%), and used the remaining 19 C-complex, 1 D-type, and 1 T-type asteroids (Supplementary Figure 1). We used Bus-DeMeo taxonomy as summarized by Hasegawa et al (2017).…”

“…In order to discuss the possible contribution of brucite to 3.1 µm absorption while observing its 2.4 µm absorption, we combined the reflectance spectra acquired using AKARI (Usui et al, 2019) and ground-based observations (Bus & Binzel, 2002;DeMeo et al, 2009;Takir & Emery, 2012) for > 2.5 µm and < 2.5 µm, respectively. Data were compiled by Hasegawa et al (2017).…”

The appearance of a 'fresh' surface on 596 Scheila as a consequence of the 2010 impact event

“…Vernazza et al (2015) stated that most surfaces of dark C-and Xcomplex and D-type (including T-type) asteroids have not been collected as meteorites on Earth, but only as anhydrous chondritic porous interplanetary dust particles (IDPs). Hasegawa et al (2017) also pointed out that in addition to their spectroscopic properties, the radar and polarization properties of these bodies indicate that they are related to chondritic porous IDPs. Most dark X-complex and D-type asteroid surfaces have been shown to have anhydrous surface compositions by spectroscopic observations in the 3-µm wavelength region (e.g., Takir & Emery 2012;Usui et al 2019), and 596 also has anhydrous surface layers, which indicates an association with chondritic porous IDPs (Figure 2).…”