9:30 AM - 9:45 AM
[PPS03-08] Stereoscopic shape measurements of Ryugu samples for curation catalog and texture analysis
Remote-sensing observations of asteroid Ryugu have shown that its boulders can be classified into several types based on surface textures and reflectance spectra, and different types of boulders may have experienced different parent body processes [1]. The presence of such different types of shapes have been confirmed in the returned samples mm to sub-mm in diameter [2]. Close-up images of Ryugu boulders taken by an optical camera MASCAM onboard the MASCOT lander has been investigated with a number of quantitative indices, such as fractal dimension and root-mean square (RMS) slope [3]. Furthermore, boulders with reflectance significantly higher than the Ryugu's average have been found on the surface of Ryugu and are called bright boulders [4-6]. Their size frequency distribution suggests that as much as sub-percent level of small fragments of bright boulders could be contained in the returned samples. In fact, a large number of bright boulders have been observed in the optical images of the returned samples. However, many of the apparent bright spots can be caused by specular reflection on sample surfaces. In order to distinguish between actual bright materials and specular reflections, precise measurement of the sample geometry is needed [7,8]. In this study, as a part of the return sample curation, we measured the three-dimensional shape of individual particles by stereo imaging.
We developed a measurement system that can take images from different viewing angles by rotating a small CMOS camera around a rotation axis tilted by 15 degrees [8] and took images of a total of 69 particles of the Ryugu samples, which are to be distributed upon the international AO. For each particle, the camera orientation angle was changed by 6-degree increments over full angular range of 180-210 degrees. The pixel resolution of the camera was 1.9 μm/pix. A group of about 30 images per particle was analyzed using a commercial software Metashap based on shape-from-motion method to generate a high-resolution digital elevation model (DEM). In this study, we created DEM with a face element diameter of about 15 pix (about 30 μm). In order to examine the robustness of our analysis, DEMs were obtained from image sets with two different increments (i.e., 3-deg and 6-deg) and confirmed that volumes agree with each other within ~10% of error.
Some of the returned samples showed smooth surfaces, while others had rough volcanic rock-like surfaces (Fig 1). There were four particles whose top surface appeared to be composed of two large surfaces, which accounted for about 6% of the total (for example, A0034, Fig 1). The angle θ of face elements of the obtained DEM was defined as the surface-normal angle of the of each face element measured from the height direction of the particles (Fig 2). Particles with smooth surfaces had significantly less dispersion of θ than rough particles. In our presentation, we plan to discuss the characteristics of the Ryugu particles obtained by using this index.
Reference: [1] Sugita et al. (2019), Science, 364, eaaw0422, [2] Tachibana et al. (2022) Science, abj8624. [3] Otto et al. (2021), MNRAS, staa3314, [4] Tatsumi et al. (2021) Nature Astron. 5, 39-45, [4] Sugimoto et al. (2021a) Icarus 114529. [6] Sugimoto et al. (2021b) Icarus 114591. [7] Yada et al. (2021) Nature Astron. 1-7 [8] Cho et al. PSS, under review.
We developed a measurement system that can take images from different viewing angles by rotating a small CMOS camera around a rotation axis tilted by 15 degrees [8] and took images of a total of 69 particles of the Ryugu samples, which are to be distributed upon the international AO. For each particle, the camera orientation angle was changed by 6-degree increments over full angular range of 180-210 degrees. The pixel resolution of the camera was 1.9 μm/pix. A group of about 30 images per particle was analyzed using a commercial software Metashap based on shape-from-motion method to generate a high-resolution digital elevation model (DEM). In this study, we created DEM with a face element diameter of about 15 pix (about 30 μm). In order to examine the robustness of our analysis, DEMs were obtained from image sets with two different increments (i.e., 3-deg and 6-deg) and confirmed that volumes agree with each other within ~10% of error.
Some of the returned samples showed smooth surfaces, while others had rough volcanic rock-like surfaces (Fig 1). There were four particles whose top surface appeared to be composed of two large surfaces, which accounted for about 6% of the total (for example, A0034, Fig 1). The angle θ of face elements of the obtained DEM was defined as the surface-normal angle of the of each face element measured from the height direction of the particles (Fig 2). Particles with smooth surfaces had significantly less dispersion of θ than rough particles. In our presentation, we plan to discuss the characteristics of the Ryugu particles obtained by using this index.
Reference: [1] Sugita et al. (2019), Science, 364, eaaw0422, [2] Tachibana et al. (2022) Science, abj8624. [3] Otto et al. (2021), MNRAS, staa3314, [4] Tatsumi et al. (2021) Nature Astron. 5, 39-45, [4] Sugimoto et al. (2021a) Icarus 114529. [6] Sugimoto et al. (2021b) Icarus 114591. [7] Yada et al. (2021) Nature Astron. 1-7 [8] Cho et al. PSS, under review.