¹Tetsushi Sakurai, ²Takuya Ishizaki, ¹Akiko M. Nakamura
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116729]
¹Department of Planetology, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe-city, Hyogo 657-8501, Japan
²Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara-city, Kanagawa 252-5210, Japan
Copyright Elsevier

Planetesimals underwent consolidation processes in the early solar system, which altered their thermal and mechanical properties. Sintering—a process that forms solid necks between particles—is considered one such process in planetesimals, influencing their filling factor, or porosity, as well as their thermal and mechanical properties.
In this study, to better constrain and understand the thermal and mechanical properties of planetesimals that evolved from initially powdery or granular bodies, as well as those of boulders on small bodies, which are considered remnant planetesimals, we prepared porous sintered samples consisting of glass particles with filling factors ranging from 0.35 to 0.75, corresponding to porosities of 65 % to 25 %. We then measured their thermal diffusivity, elastic wave velocity, and flexural strength, and derived empirical relationships for the normalized values—scaled by those at a filling factor of 1—as functions of filling factor or porosity. The normalized thermal diffusivities and elastic wave velocities of the sintered glass materials in this study showed similar dependencies on the filling factor. Moreover, the upper limits of the normalized elastic wave velocities were consistent with those of snow at corresponding filling factors, suggesting that these upper limits may be independent of the matrix material.
The derived empirical relationships apply to materials with porosities higher than those of meteorites. We estimated the porosity of a low-thermal-inertia boulder on the surface of asteroid Ryugu based on its thermal inertia, assuming no influence from internal cracks. The result suggests that the boulder’s porosity may be higher than values previously reported, and should be regarded as one of the possible porosity estimates.