Speaker
Description
On September 26, 2022, the NASA DART (Double Asteroid Redirection Test) spacecraft
struck Dimorphos, the moonlet of Didymos, to test near-Earth object deflection via impact for planetary defence [1]. As well as causing a change in Dimorphos’ orbital period [2], the impact caused a massive dust cloud to be ejected from the surface, e.g. [3,4]. By studying the characteristics and behaviour of the ejecta cloud, the DART mission offered a rare opportunity to peer under the surface of an asteroid and further our understanding of their global properties.
Didymos-Dimorphos was monitored in polarimetric mode before and after the impact
[5,6]. Post-impact measurements revealed a significant drop in polarisation, suggesting
differences between the ejecta material and that on the original regolith surface.
Remarkably, even months after the impact, the polarisation remained persistently lower than pre-impact, despite photometric measurements showing that the system’s brightness had returned to “normal” ~23 days post-impact [7]. This suggests the presence of residual ejecta material still within the system months after the impact, either in orbit or deposited on the asteroid surface(s). This highlights the sensitivity of polarimetric measurements, revealing
details often unattainable from traditional observational techniques.
In this presentation, we will be discussing these previous results, as well as presenting new polarimetric measurements obtained with VLT this year. In 2024, Didymos-Dimorphos is making another close approach to Earth, allowing us to study the system around two years after the DART impact. Our goal with these observations is to establish whether the polarisation of the system has returned to the pre-impact level or remains at the lower post-impact level and, thus, clarify if or how much ejecta material remains in the system. This may ultimately benefit the Hera team [8] for planning the spacecraft trajectory to avoid damage by impacts of dust particles.
[1] Daly, R., et al. (2023), Natur, 616, 443; [2] Thomas, C. A., et al. (2023), Natur, 616, 448; [3] Li, J.-Y., et al. (2023), Natur, 616, 452; [4] Opitom, C., et al. (2023), A&A, 671, L11; [5] Bagnulo, S., et al. (2023), ApJL, 945, L38; [6] Gray, Z., et al. (2024), PSJ, 5, 18; [7] Graykowski, A., et al. (2024), Natur, 616, 452; Michel, P., et al. (2018), AdSpR, 62, 2261.
