Optical Characterization of the DART Impact Plume: Importance of Realistic Ejecta Scattering Properties

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The NASA Double Asteroid Redirection Test (DART) spacecraft successfully crashed on Dimorphos, the secondary component of the binary (65803) Didymos system. Following the impact, a large dust cloud was released, and a long-lasting dust tail developed. We have extensively monitored the dust tail from the ground and the Hubble Space Telescope. We provide a characterization of the ejecta dust properties, i.e., particle size distribution and ejection speeds, ejection geometric parameters, and mass, by combining both observational data sets and using Monte Carlo models of the observed dust tail. The size distribution function that best fits the imaging data is a broken power law having a power index of –2.5 for particles of r ≤ 3 mm and –3.7 for larger particles. The particles range in size from 1 μm up to 5 cm. The ejecta is characterized by two components, depending on velocity and ejection direction. The northern component of the double tail, observed since 2022 October 8, might be associated with a secondary ejection event from impacting debris on Didymos, although is also possible that this feature results from the binary system dynamics alone. The lower limit to the total dust mass ejected is estimated at ∼6 × 106 kg, half of this mass being ejected to interplanetary space.

Section: Simple Monte Carlo Modelingmentioning

confidence: 99%

Characterization of the Ejecta from the NASA/DART Impact on Dimorphos: Observations and Monte Carlo Models

Moreno,

Bagatin,

Tancredi

et al. 2023

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“…The fading slows down, from initially being 0.115 ± 0.003 mag day −1 (in the 2″ aperture) and 0.086 ± 0.003 mag day −1 (in the 5″ aperture) over the first week to 0.057 ± 0.003 mag day −1 (2″) and 0.068 ± 0.002 mag day −1 (5″). This fading rate convolves the rate of ejecta escaping the system with solar-phase-angle effects that are different for different ejecta size regimes (Lolachi et al 2023). In the phase-angle regime covered by our observations the brightness of very fine submillimeter material should appear to increase slightly, while for larger (millimeter to centimeter) material it should drop, and drop even faster for larger boulders (meter sized) and for the asteroids themselves.…”

Section: Light-curve Analysismentioning

confidence: 99%

Optical Monitoring of the Didymos–Dimorphos Asteroid System with the Danish Telescope around the DART Mission Impact

Rożek,

Snodgrass,

Jørgensen

et al. 2023

The NASA’s Double-Asteroid Redirection Test (DART) was a unique planetary defence and technology test mission, the first of its kind. The main spacecraft of the DART mission impacted the target asteroid Dimorphos, a small moon orbiting the asteroid Didymos (65803), on 2022 September 26. The impact brought up a mass of ejecta which, together with the direct momentum transfer from the collision, caused an orbital period change of 33 ± 1 minutes, as measured by ground-based observations. We report here the outcome of the optical monitoring campaign of the Didymos system from the Danish 1.54 m telescope at La Silla around the time of impact. The observations contributed to the determination of the changes in the orbital parameters of the Didymos–Dimorphos system, as reported by Thomas et al., but in this paper we focus on the ejecta produced by the DART impact. We present photometric measurements from which we remove the contribution from the Didymos–Dimorphos system using an H–G photometric model. Using two photometric apertures we determine the fading rate of the ejecta to be 0.115 ± 0.003 mag day−1 (in a 2″ aperture) and 0.086 ± 0.003 mag day−1 (5″) over the first week postimpact. After about 8 days postimpact we note the fading slows down to 0.057 ± 0.003 mag day−1 (2″ aperture) and 0.068 ± 0.002 mag day−1 (5″). We include deep-stacked images of the system to illustrate the ejecta evolution during the first 18 days, noting the emergence of dust tails formed from ejecta pushed in the antisolar direction, and measuring the extent of the particles ejected Sunward to be at least 4000 km.

“…As determined by mapping >90 ∼meter-sized boulders, the distribution of the boulders that can be tracked in the LICIACube images shows clustering in an ejection direction nearly perpendicular to DARTʼs incoming trajectory, in the direction of Dimorphos' south pole, with a speed of tens of meters per second (Farnham et al 2023). Efforts to provide additional constraints on the ejecta properties from modeling LICIACube images are ongoing (Kolokolova et al 2022;Lolachi et al 2023;Ivanovski et al 2024).…”

Section: Ejecta Observations and Evolutionmentioning

confidence: 99%

Achievement of the Planetary Defense Investigations of the Double Asteroid Redirection Test (DART) Mission

Chabot,

Rivkin,

Cheng

et al. 2024

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NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β, resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.