Modelling Palomar Transients: Constraints from Reflection Geometry and Orbital Altitude
Abstract
Recent searches of digitised photographic plates from the Palomar Observatory have uncovered tens of thousands of short-lived transients, each visible in only a single exposure. Their morphologies indicate sub-second flashes, consistent with specular reflections from highly reflective objects in near-Earth orbits. In this paper, we present a modelling study using geometric shadow modelling, Monte Carlo simulations, and photometric constraints to infer their physical properties. We examine the observed groupings and alignments, which appear to be consistent with sudden changes in attitude. Assuming a spherical-shell model, the angular profile of the measured transient deficit around the antisolar point is consistent with a population at characteristic altitudes of ∼ 20,000--25,000 km. A complementary estimate, based on the altitude dependence of the global Earth-shadow deficit, yields a broader characteristic range of ∼ 20,000--35,000 km above Earth's surface, extending into the geosynchronous orbital (GSO) region. Under simplified geometric and photometric assumptions and assuming ∼20,000 to 35,786 km above the Earth's surface, the inferred sizes of the specularly reflecting facets range from centimetre scales up to ∼3 m, with characteristic flash durations of ∼320 ms and slow rotation rates. We explore both natural and non-natural toy models consistent with the data, and provide constraints to guide future observational searches.
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BibTeX
@misc{villarroel2026modelling,
title = {{Modelling Palomar Transients: Constraints from Reflection Geometry and Orbital Altitude}},
author = {Beatriz Villarroel and Alina Streblyanska and Hichem Guergouri and Brian Doherty and Matthew Shultz and Stephen Bruehl},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.05105},
eprint = {2609.05105},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.05105},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Modelling Palomar Transients: Constraints from Reflection Geometry and Orbital Altitude
AU - Beatriz Villarroel
AU - Alina Streblyanska
AU - Hichem Guergouri
AU - Brian Doherty
AU - Matthew Shultz
AU - Stephen Bruehl
PY - 2026
DA - 2026/09/04
PB - arXiv
DO - 10.48550/arxiv.2609.05105
UR - https://arxiv.org/abs/2609.05105
AB - Recent searches of digitised photographic plates from the Palomar Observatory have uncovered tens of thousands of short-lived transients, each visible in only a single exposure. Their morphologies indicate sub-second flashes, consistent with specular reflections from highly reflective objects in near-Earth orbits. In this paper, we present a modelling study using geometric shadow modelling, Monte Carlo simulations, and photometric constraints to infer their physical properties. We examine the observed groupings and alignments, which appear to be consistent with sudden changes in attitude. Assuming a spherical-shell model, the angular profile of the measured transient deficit around the antisolar point is consistent with a population at characteristic altitudes of ∼ 20,000--25,000 km. A complementary estimate, based on the altitude dependence of the global Earth-shadow deficit, yields a broader characteristic range of ∼ 20,000--35,000 km above Earth's surface, extending into the geosynchronous orbital (GSO) region. Under simplified geometric and photometric assumptions and assuming ∼20,000 to 35,786 km above the Earth's surface, the inferred sizes of the specularly reflecting facets range from centimetre scales up to ∼3 m, with characteristic flash durations of ∼320 ms and slow rotation rates. We explore both natural and non-natural toy models consistent with the data, and provide constraints to guide future observational searches.
ER -