[M-ZZ40] International initiatives and cooperation in planetary defense

[MZZ40-P02] Polarimetric observations of Didymos-Dimorphos surfaces and surface materials before and after the DART impact

★Invited Papers

*Tomohiko Sekiguchi¹, Jooyeon Geem², Masateru Ishiguro², Hiroyuki Naito³, Bach P Yoonsoo⁴, Seiko Takagi⁵, Tatsuharu Ono⁵, Hirohide Demura⁶ (1.Hokkaido University of Education, 2.Seoul National University, 3.Nayoro Observatory, 4.Korea Astronomy and Space Science Institute, 5.Hokkaido University, 6.Aizu University)

Keywords:asteroids, ground-based polarimetric observations, DART spacecraft, Hera spacecraft, impact, planetary difense

We performed polarimetric observations of a binary asteroid system, Didymos and Dimorphos before and after the impact of the DART spacecraft using the 1.6-m Pirka Telescope at the Nayoro Observatory of the Faculty of Science, Hokkaido University. We found that the polarization phase curve (PPC) is comparable with S-type asteroids throughout the whole observing period, covering before and after the impact on Dimorphos and its subsequent dust ejection from Dimorphos. The geometric albedo of the binary system derived from the polarization slope (h = 0.092) is pV = 0.21, in accordance with the average value of the S-type asteroids.
We emphasize that the polarization degree after a PPC correction indicates no significant change in the polarization degree before and after the impact experiment, al- though our post-impact photometry indicates that the large (>∼100 microns) particles ejected from Dimorphos account for the large fraction (∼50 %) of the entire scattering cross-section within 2 days. The PPC of an asteroid depends primarily on the number of multiple scat- tering. Accordingly, our polarimetry indicates (i) Didymoon is composed of material similar to Dimorphos, implying the same origin, and (ii) the significant contribution of ”multiple scattering within a single particle” to the PPC of S-type asteroids.