Abstract
Abstract We analyze images of a rock on Ryugu acquired in situ by MASCam, the camera on the mascot lander, with the aim of identifying possible carbonaceous chondrite (CC) analogs. The rock’s reflectance ( r F = 0.034 ± 0.003 at phase angle 4.5 ∘ ± 0.1 ∘ ) is consistent with Ryugu’s average reflectance, suggesting that the rock is typical for this asteroid. A spectrophotometric analysis of the rock’s inclusions provides clues to its CC group membership. Inclusions are generally brighter than the matrix. The dominant variation in their color is a change in the visible spectral slope, with many inclusions being either red or blue. Spectral variation in the red channel hints at the presence of the 0.7 μm absorption band linked to hydrated phyllosilicates. The inclusions are unusually large for a CC; we find that their size distribution may best match that of the Renazzo (CR2) and Leoville (CV3) meteorites. The Ryugu rock does not easily fit into any of the CC groups, consistent with the idea that typical Ryugu-type meteorites are too fragile to survive atmospheric entry.
Highlights
On 3 October 2018, mascot was released by the Hayabusa2 spacecraft to land on the small near-Earth asteroid 162173 Ryugu (Ho et al 2017)
In the previous sections we determined the reflective properties of the Ryugu rock and its inclusions and derived the size distribution for the latter
We should be in a position to choose the most appropriate carbonaceous chondrite (CC) analog group for Ryugu rocks from the perspective of MASCam
Summary
On 3 October 2018, mascot was released by the Hayabusa spacecraft to land on the small near-Earth asteroid 162173 Ryugu (Ho et al 2017). Data acquired by mascot during its 17-hour long mission revealed the surface of this C-type asteroid in unprecedented detail. The MASCam camera acquired a total of 120 images, of which 65 show Ryugu’s surface (Jaumann et al 2019). MASCam was equipped with LEDs in four colors, covering the visible wavelength range to the near-infrared, to allow imaging at night. Close-up night-time imaging of a small rock in front of the lander revealed abundant multi-colored inclusions set in a dark matrix that resemble those in chondritic meteorites. Mascot’s fourth instrument, the MicrOmega near-IR spectrometer (Bibring et al 2017), appears not to have acquired useful data. Only MASCam performed an in situ spectral characterization of Ryugu’s surface
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