Bulk density of small meteoroids

The purpose of our work is to determine the bulk density of meteoroids. Unlike previous works which focused either on the dynamical properties of the meteoroids (deceleration), ignoring fragmentation; or on fitting solely the lightcurves, neglecting the dynamics of the meteoroids, we use both the photometry and astrometry to constrain our model. Our model, based on the dustball model, considers the meteoroid to be a collection of grains held together by a lower boiling point \u27glue\u27. It uses conservation of energy and momentum to model the change in velocity and the light production as a function of time. The free parameters in the model (mass, density, heat of ablation, temperature of fragmentation, boiling temperature, specific heat, molar mass, and thermal conductivity) are varied from values consistent with fragile cometary material, through asteroidal chondritic material, to solid iron, and the entire parameter space is explored, giving all possible solutions which are consistent with the data. An initial study used cameras with small fields of view to achieve high spatial resolution. 42 meteors were detected, but only six meteors were entirely captured in the common observing volume of the cameras, and were therefore suitable for modelling. The modelling revealed that taking fragmentation into account does not necessarily produce high bulk density values, but the fraction of high density (nearly iron composition) meteoroids observed was higher than expected. This study showed that the fraction of small meteoroids with high bulk density (almost iron density) may be underestimated. In order to analyse more data, a model of detector saturation was developed to correct for meteors which were saturated on the 8-bit camera systems. The model was tested on data collected in a special campaign, and found to reproduce the unsaturated lightcurves correctly. This saturation correction was found to be very important in correctly modelling the brighter meteors in the dataset for the final study. Finally, 92 meteors were recorded on wider field systems using higher resolution detectors to measure deceleration precisely. Densities for each meteoroid was calculated, and the meteoroids were grouped by their orbital characteristics for analysis. As expected, meteoroids with asteroidal origins had high densities of 4200 kg m-3 in average, and those with Halley-type cometary orbits had low densities ranging from 380 kg m-3 to 1510 kg m-3. The asteroidal densities are higher than chondritic, suggesting that some have significant iron content. Meteoroids from the Perseid meteoroid stream had densities of 620±200 kg m-3, consistent with the sporadic Halley-type meteoroids. Most surprising result was the high density of Jupiter-family comets (3100±300 kg m-3 for Jupiter-family sporadics, and 3200 kg m-3 in average for the North Iota Aquariids, which are linked to Comet 2P/Encke). This suggests that refractory material may be a major component of Jupiter family comets in agreement with the surprising results of the Stardust mission on comet 81P/Wild 2

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role.Comment: 16 pages, 5 Figures, accepted in the Astrophysical Journal Letters (ApJL) on October 16, 202

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos’s orbit substantially, largely from the ejection of material. We present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ∼1.4 mag, we find consistent dimming rates of 0.11–0.12 mag day−1 in the first week, and 0.08–0.09 mag day−1 over the entire study period. The system returned to its pre-impact brightness 24.3–25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role

Photometry of the Didymos System across the DART Impact Apparition

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact

Ejecta Evolution Following a Planned Impact into an Asteroid:The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role