arXiv subjects

Sophie E. Deam

Publications and source records attributed to Sophie E. Deam.

9 recordsLinked to original sources

arXiv2026

High-Speed Observations of Lunar Impact Flashes

Lunar impact flashes provide a direct means of estimating the flux of centimetre-sized meteoroids impacting the lunar surface. However, 25-60 frames per second imaging typical of most monitoring programs limit the ability to resolve the rapid temporal evolution of the impact process, while the integration of Earthshine background restricts the detection of faint flashes. In this work, we present high-speed observations of lunar impact flashes captured at 200 and 250 FPS using the Zadko Telescope in Western Australia. We resolve the light curves of four confirmed events, revealing complex morphologies, some of which are not well modelled by simple exponential decays. One event was simultaneously detected by a second observer using a 50 FPS system, revealing a significantly faster brightness drop in the high-speed data that cannot be explained by spectral differences alone, indicating temporal integration of the vapour plume and subsequent ejecta. Our data also indicates that the initial flash intensity (representing the vapour plume) exhibits significantly less variance across events than the total luminous energy. Furthermore, we found no statistical correlation between the initial luminous energy and the total integrated energy of the flashes in this data, suggesting that the physical mechanism driving the initial vapour expansion may be physically decoupled from the longer-duration glow driven by the cooling ejecta. High temporal resolution combined with high sensitivity are therefore essential for accurately characterising the physical properties of the impactor and distinguishing the initial vapour plume from the subsequent incandescent cooling phase, although a significantly larger dataset is required to definitively constrain these mechanisms.

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arXiv2026

A Cloud-Based Tool for Meteorite Recovery Using Drones and Machine Learning

We present a cloud-based tool that uses drones and machine learning to help recover instrumentally observed meteorite falls. We showcase a collection of improvements made upon previous iterations of our system, as well as detail the successes and limitations of this technique when applied to observed meteorite falls in South and Western Australia. This tool is available to the meteoritics research community upon request at https://find.gfo.rocks.

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arXiv2026

Simulated LSST Observations of Real Metre-scale Imminent Impactors

As of mid-2026, 11 objects have been discovered prior to impacting the Earth, with warning times between 2 - 20 hours. Using real metre-sized Earth impactors from the last decade, we ask the question: ``If the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) had been operating over the last decade, how many imminent impactors would it have observed and discovered pre-impact, and how early would these discoveries have been?'' We use the LSST Solar System Survey Simulator Sorcha and a population of real fireballs observed by orbital sensors over the last decade to investigate which events would have been observed pre-impact. We find that the LSST would have observed 30 (13.9%) of the 216 simulated objects, with most objects receiving 2 - 4 observations. Using the default linking algorithm, only two (0.9%) of these objects would have been `discovered' pre-impact. Using a modified linking algorithm better suited to fast moving objects, this increases to eight (3.7%). Based on this, we predict that the LSST will discover 8 +/- 2 imminent impactors over its nominal 10 year survey, at the low end of previous estimations. However, we predict these objects to be discovered 4 days pre-impact, substantially earlier than the current average. This will bring significant opportunities for telescopic follow-up, targeted fireball observations, planetary defence planning, and public engagement. There is also significant potential for precovery for impactors observed by the LSST but discovered by other surveys, instantly lengthening observation arcs and thereby reducing the orbital and impact location uncertainties. In some cases, these observations may also enable the linkage of telescopic observations with observed fireballs post-impact, providing valuable pre-impact astrometric and photometric data. This has significant implications for both asteroid research and planetary defence.

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arXiv2025

A Near-Earth Object Model Calibrated to Earth Impactors

The population of Earth-impacting meteoroids and its size-dependent orbital elements are key to understanding the origin of meteorites and informing on planetary defence efforts. Outstanding questions include the role of collisions in depleting meteoroids on highly evolved orbits and the relative importance of delivery resonances. Those depend on size, with current dynamical models considering only asteroids larger than 10m in diameter. Based on 1,202 sporadic meteoroids observed by the Global Fireball Observatory, we created a debiased model of the near-Earth meteoroid population in the 10g - 150kg in size (approximately 1cm - 0.5m) as they dynamically evolved from the main asteroid belt onto Earth-crossing orbits. The observed impact population is best matched with a collisional half-life decreasing from 3Myr for meteoroids of 0.6kg (7cm) or higher, to 1Myr below this size, extending to the model lower bound of 10g. Placing our results in context with near-Earth object models for larger sizes, we find that the inner main belt continues to dominate feeding the small 1m to 10m diameter population primarily via the $ν_6$ secular resonance and the 3:1J mean motion resonance. We also evaluated the potential significance of physical processes other than collisions on Earth-impacting meteoroids, such as low-perihelion disruptions from thermal stresses.

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arXiv2025

Starkiller: subtracting stars and other sources from IFU spectroscopic data through forward modeling

We present starkiller, an open-source Python package for forward-modeling flux retrieval from integral field unit spectrograph (IFU) datacubes. Starkiller simultaneously provides stellar spectral classification, relative velocity, and line-of-sight extinction for all sources in a catalog, alongside a source-subtracted datacube. It performs synthetic difference imaging by simulating all catalog sources in the field of view, using the catalog for positions and fluxes to scale stellar models, independent of the datacube. This differencing method is particularly powerful for subtracting both point-sources and trailed or even streaked sources from extended astronomical objects. We demonstrate starkiller's effectiveness in improving observations of extended sources in dense stellar fields for VLT/MUSE observations of comets, asteroids and nebulae. We also show that starkiller can treat satellite-impacted VLT/MUSE observations. The package could be applied to tasks as varied as dust extinction in clusters and stellar variability; the stellar modeling using Gaia fluxes is provided as a standalone function. The techniques can be expanded to imagers and to other IFUs.

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arXiv2025

Recent Chemo-morphological Coma Evolution of Comet 67P/Churyumov-Gerasimenko

We present VLT/MUSE observations of comet 67P/Churyumov-Gerasimenko during its 2021 perihelion passage, from which we generated simultaneous maps of dust, [OI], C$_2$, NH$_2$, and CN comae across 12 pre- and post-perihelion epochs. These maps reveal the evolutionary and compositional trends of 67P's coma and further enrich the context and findings of ESA's Rosetta mission. Dust and gas species displayed distinct structures, where NH$_2$ and CN signals were uniquely associated with known dust fans, raising the question of possible correlation to the dust and contributions of extended sources. Localised fitted NH$_2$ scale lengths were 1.5-1.9$\times$ larger than those fitted for the rest of the coma, which is consistent with an extended source component for northern pre-perihelion emissions. In the southern hemisphere, CN was correlated with a prominent and sharp dust structure, potentially revealing an extended source origin via larger dust particles that preserve the CN parent species, as evidenced by higher spectral slopes in the region. Gas maps depicted two distinct evolutionary regimes: (1) evolving H$_2$O ([OI]$^{1}$D) and C$_2$ emissions driven by nucleus sublimation and subsolar insolation, and (2) stable NH$_2$ and CN emissions associated with seasonal dynamics and possible distributed sources. Dust spectral slope maps revealed spectral slope trends consistent with Rosetta findings, while green/red [OI] ratios generally indicate a coma dominated by H$_2$O.

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arXiv2025

Snapshot of a new interstellar comet: 3I/ATLAS has a red and featureless spectrum

The interstellar comet 3I/ATLAS is only the third interstellar object to be discovered. Pre-perihelion measurements provide a unique opportunity to study its activity and composition, which may alter as it is heated in the coming months. We provide an initial baseline from optical spectroscopic observations obtained only two days after discovery, using the MUSE instrument on the VLT on 2025 July 3, while 3I was at 4.47 au from the Sun and 3.46 au from the Earth. These observations confirm the cometary nature of 3I, and reveal a red coma with a spectral slope of $(18\pm4)\%/1000$~Å, redder than most Solar System comets but similar to the surface colour of some Solar System Trans-Neptunian Objects or Centaurs. We searched for but did not detect gas emission from C$_2$, NH$_2$, CN, and [OI], which is consistent with volatile non-detections for Solar System comets at this heliocentric distance. At present, the coma appears entirely dusty. Future observations of 3I as it comes closer to the Sun will provide an invaluable opportunity to witness the evolution of its activity, study its composition, test predictions of interstellar object population models, and compare 3I to Solar System comets.

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arXiv2025

A portrait throughout perihelion of the NH$_2$-rich interstellar comet 2I/Borisov

The interstellar comet 2I/Borisov is the first interstellar object where compositional characterisation was possible throughout its entire perihelion passage. We report all 16 epochs of a comprehensive optical observation campaign with ESO VLT's integral field spectrograph MUSE, spanning 126 days from 2019 November 14 to 2020 March 19. The spatial dust emission of 2I/Borisov was predominantly smooth, with no seasonal effect. A jet-like feature was consistently visible. The gas production morphology of its coma was also smooth and similar for C$_2$, NH$_2$, and CN: symmetric around the photocentre. The production rates of these species gently declined into and beyond perihelion, until 2I's outburst and splitting event in early 2020 March. C$_2$, NH$_2$, and CN production rates all increased, with NH$_2$ being the most significant; the dust emission also slightly reddened. 2I/Borisov is a carbon-depleted, relatively NH$_2$-rich comet when compared to those comets yet measured in the Solar System.

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arXiv2025

Perihelion history and atmospheric survival as primary drivers of the Earth`s meteorite record

Models predict that more than half of all impacting meteoroids should be carbonaceous, reflecting the abundance of carbon-rich asteroids in the main belt and near-Earth space. Yet carbonaceous chondrites represent only about 4% of meteorites recovered worldwide. Here we analyse 7,982 meteoroid impacts and 540 potential meteorite falls from 19 global observation networks and demonstrate that intense thermal stress at low perihelion distances coupled with the filtering effect of Earth`s atmosphere explains this mismatch. Meteoroids repeatedly subjected to intense thermal cycling near the Sun fracture and weaken, removing the most friable objects even before atmospheric entry. Our data also show that tidally disrupted meteoroid streams produce especially fragile fragments that rarely survive to the ground. Consequently, compact, higher-strength, thermally cycled bodies dominate the meteorite record. These findings reconcile the predicted carbonaceous flux with its scarcity in collections, underscoring how orbital evolution and atmospheric filtering shape the materials that reach Earth`s surface.

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