Physical properties of the Didymos system before and after the DART impact

Abstract

Context. On September 26, 2022, the Double Asteroid Redirection Test (DART) successfully changed the trajectory of the asteroid Dimorphos (i.e. 65803 Didymos I), a satellite circling (65803) Didymos. Aims. We aim to characterize the consequence of this collision and derive the physical properties of the ejecta features based on ground-based observations in East Asia. Methods. Filtered photometric observations were made between September 21 2022 (~5 days before DART impact) and January 5 2023 using the Lulin 1-m telescope to identify the taxonomy, size, and rotational period of Didymos. The Finson-Probstein dust dynamical models were used to determine the grain sizes (mm–cm) released after the DART impact and the date of the activity. Results. We report a rapid increase in the brightness by about one order of magnitude after the impact, to be followed by a gradual 0.07 mag decrease over the first two weeks producing a relatively shallow brightness slope at the end of October. The size and rotation period at post-impact were 0.7−0.10+0.12 km and 2.27 h, respectively. The Principal Component Index (PCI), relative reflectance, and colors were all classified as S-complex. The Dydimos system became bluer after the collision before returning to its original color. The formation of a comet-like trail containing debris in the anti-sunward direction can be explained by expansion driven by the pressure of solar radiation. A Finson-Probstein modeling approach led to an estimate of the grain size in the mm-cm range. The splitting of the tail into two components is shown in the image acquired on October 12, which may possibly be interpreted as being due to the secondary impact of fallback ejecta about a week after DART.

VLT/MUSE Characterization of Dimorphos Ejecta from the DART Impact

“…1. We followed the morphological evolution of the ejecta cone from dusty edges to detached wings in the weeks after impact, akin to what is identified by HST (Li et al 2023) and other studies (Lin et al 2023;Rożek et al 2023). We measured an SRP-induced blowback velocity of 0.85 m s −1 at the base of the northern wing and derived a distribution of maximum grain sizes that could correspond with the velocity.…”

“…As described by Moreno et al (2022), Li et al (2023), andLin et al (2023), following the formation of the ejecta cone, the initial micron to submillimeter ejecta was quickly scattered by gravitational interactions with the binary and rapidly accelerated out of the system by SRP, which formed the primary dust tail first observed in WFM at T + 0.22D after impact. Intriguingly, we observed in WFM the formation of a secondary tail around October 3 (T+6.4D) after impact, which manifested as a positive skew in brightness profiles of the primary tail until it eventually became fully resolved by October 14 (T+17.3D) after impact.…”

“…In the next few hours post-impact, the fast ejecta cleared the vicinity of the binary system, which allowed for in-depth photometric, spectroscopic, and morphological characterization of the impact ejecta. Further studies by Kareta et al (2023), Li et al (2023), Lin et al (2023), and Rożek et al (2023) found that the system faded with time as ejecta left the binary system, although a slight pause in fading was observed between October 1 and 3 (discussed in Section 3.2.2). Opitom et al (2023) used preliminary Multi-Unit Spectroscopic Explorer (MUSE) data to probe the ejecta cloud for any evidence of subsurface volatile species that may have been vaporized or excavated by the impact and found that the ejecta was likely volatile-free.…”

“…Opitom et al (2023) used preliminary Multi-Unit Spectroscopic Explorer (MUSE) data to probe the ejecta cloud for any evidence of subsurface volatile species that may have been vaporized or excavated by the impact and found that the ejecta was likely volatile-free. Finally, Li et al (2023), Lin et al (2023), and Opitom et al (2023) extensively characterized the morphological evolution of the ejecta from just after impact to up to a month post-impact, which revealed numerous dust features such as the wide eastern-facing ejecta cone, diffuse surrounding ejecta cloud, various clumps and linea, spirals, wings, and the formation of two dust tails.…”

“…Therefore, SRP preferentially influenced particles based on mass and size and more rapidly accelerated and altered the trajectories of smaller lighter particles, while larger heavier particles required longer timescales for SRP effects to become prominent. Models by Lin et al (2023) suggested that SRP was the key force in the formation of the primary dust tail, which formed just hours post-impact and expanded at 31 m s −1 in the anti-sunward direction on September 27. Finally, work by Li et al (2023) further established that by the September 29 Hubble Space Telescope (HST) observations the majority of ejecta evolution was no longer governed by gravitational regimes, but rather by SRP-induced evolution.…”