Spectrophotometric analysis of the Ryugu rock seen by MASCOT: Searching for a carbonaceous chondrite analog

We analyze images of a rock on Ryugu acquired in situ by MASCam, camera of the MASCOT lander, with the aim of identifying possible carbonaceous chondrite (CC) analogs. The rock's reflectance ($r_{\rm F} = 0.034 \pm 0.003$ at phase angle $4.5^\circ \pm 0.1^\circ$) 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 CC group membership. Inclusions are generally brighter than the matrix. The dominant variation in their color is a change of 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~$\mu$m 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

Spectral and Petrographic Properties of Inclusions in Carbonaceous Chondrites and Comparison with In Situ Images from Asteroid Ryugu

We imaged a set of carbonaceous chondrites from the CM2, CO3, CV3, and CK4 groups using the qualification model of MasCam, the camera on board the asteroid lander MASCOT, which touched down on asteroid Ryugu in 2018 October. A CI1 meteorite was also imaged but excluded from the analysis due to prominent terrestrial weathering. Following the methods used to image the rock on Ryugu, we placed a total of 14 meteorites approximately 20 cm in front of the camera to achieve a spatial resolution of about 0.2 mm per pixel and illuminated the samples with onboard light-emitting diodes of four different colors in the visible wavelength range. We mapped bright and dark inclusions within the meteorites and derived the inclusion brightness relative to the matrix in the red light, the relative spectral slope of each inclusion, the inclusion size frequency distribution and the matrix volume abundance. We find that the meteorite groups overlap within these parameters, but individual samples, as well as individual inclusions, can have deviating values. Terrestrial weathering appears to have no systematic influence on these parameters. Relating our analysis to the inclusions found in the rock on Ryugu, we find that the spectral parameters of Ryugu's inclusions fit well in the parameter space of the carbonaceous chondrites. Compared with the most common types of carbonaceous chondrites, Ryugu's rock has larger inclusions (mean diameter: 0.63 ± 0.91 mm) and a higher upper limit to the matrix abundance (92.4 vol%)

Ryugu as seen close up by MASCOT

In October 2018, MASCOT landed on the surface of Ryugu to start a campaign of in-situ measurements. Its brief mission was successful, with the onboard camera revealing the surface of this C-type asteroid in unpre- cedented detail. The presence of abundant mm-sized, multi-colored inclusions in one rock suggests a link between Ryugu and carbonaceous chondrites

Surface roughness of asteroid (162173) Ryugu and comet 67P/Churyumov-Gerasimenko inferred from in-situ observations

Alteration processes on asteroid and comet surfaces, such as thermal fracturing, (micrometeorite) impacts or volatile outgassing, are complex mechanisms that form diverse surface morphologies and roughness on various scales. These mechanisms and their interaction may differ on the surfaces of different bodies. Asteroid Ryugu and comet 67P/Churyumov–Gerasimenko, both, have been visited by landers that imaged the surfaces in high spatial resolution. We investigate the surface morphology and roughness of Ryugu and 67P/Churyumov–Gerasimenko based on high-resolution in situ images of 0.2 and 0.8 mm pixel resolution over an approximately 25 and 80 cm wide scene, respectively. To maintain comparability and reproducibility, we introduce a method to extract surface roughness descriptors (fractal dimension, Hurst exponent, joint roughness coefficient, root-mean-square slope, hemispherical crater density, small-scale roughness parameter, and Hapke mean slope angle) from in situ planetary images illuminated by LEDs. We validate our method and choose adequate parameters for an analysis of the roughness of the surfaces. We also derive the roughness descriptors from 3D shape models of Ryugu and orbiter camera images and show that the higher spatially resolved images result in a higher roughness. We find that 67P/Churyumov–Gerasimenko is up to 6 per cent rougher than Ryugu depending on the descriptor used and attribute this difference to the different intrinsic properties of the materials imaged and the erosive processes altering them. On 67P/Churyumov–Gerasimenko sublimation appears to be the main cause for roughness, while on Ryugu micrometeoroid bombardment as well as thermal fatigue and solar weathering may play a significant role in shaping the surface

ExoMars PANCAM High Resolution Camera (HRC): Evolution from BB to FM

This paper describes the development and testing of a focusing mechanism for the High Resolution Camera (HRC) of the ExoMars 2020 Rover. The mechanism will be used to re-position a lens barrel in order to refocus the camera. ExoMars 2020 is a cooperation between the European Space Agency and Roscosmos with a scientific contribution from NASA. The HRC is part of the PanCam (panoramic camera) which is composed of: -A Wide Angle Camera (WAC) pair, for multi-spectral stereoscopic panoramic imaging, using a miniaturised filter wheel (by TAS/RUAG/Space X and MSSL-UCL) -A High Resolution Camera (HRC) for high resolution colour image (by DLR Berlin & OHB) -PanCam Interface Unit (PIU) to provide a single electronic interface, and a PanCam Optical Bench (OB) for housing the PanCamand to provide planetary as well as dust protection (by MSSL-UCL). The HRC hardware is designed and produced by OHB System AG, Wessling and the DLR Institute for Planetary Research, Berlin. While the mechanism and the optics were developed by OHB, the focal plane and control board is under responsibility of DLR Berlin. One of the main challenges was to develop a mechanism capable of working within operational thermal environment of -55°C to +40°C (qualification level) and to survive a non-operational environment of -130°C to +50°C (qualification level). On top DHMR (dry heat microbial reduction) at +125°C had to be applied wherever possible. Cleanliness and planetary protection rules had highest priority with impact on selection of materials, lubrications, design, assembly, and testing which will be elaborated in the paper. The focus of the paper will be on the design and its evolution through the different stages from Bread Board to FM. Special attention is given to the improvements of the mechanism functionality after the breadboarding activities. In particular the QM design has been modified using a different lubrication concept (dry lubrication with gold) in order to cope with the large temperature range and high cleanliness requirements due to optics in close proximity. Additionally it will provide a detailed summary of the testing results from the BB and QM phases