Aligned, Multiple-transient Events in the First Palomar Sky Survey
TL;DR
Imagine you take a picture of the sky before satellites were ever launched, and you find some unexpected bright spots. Scientists are looking for clues as to what caused these spots—they could be reflections from objects we haven’t identified yet. This research helps us understand what might have been out there before we filled the skies with technology.
Old, digitized astronomical images taken before the human spacefaring age offer a rare glimpse of the sky before the era of artificial satellites. In this paper, we present the first optical searches for artificial objects with high specular reflections near the Earth. We follow the method proposed in Villarroel et al. and use a transient sample drawn from Solano et al. We use images from the First Palomar Sky Survey to search for multiple (within a plate exposure) transients that, in addition to being point-like, are aligned along a narrow band. We provide a shortlist of the most promising candidate alignments, including one with approximately 3.9 sigma statistical significance. These aligned transients remain difficult to explain with known phenomena, even if rare optical ghosting producing point-like sources cannot be fully excluded at present. We explore remaining possibilities, including fast reflections from highly reflective objects in geosynchronous orbit, or emissions from artificial sources high above Earth's atmosphere. We also find a highly significant (approximately 22 sigma) deficit of POSS-I transients within Earth's shadow when compared with the theoretical hemispheric shadow coverage at 42,164 km altitude. The deficit is still present though at reduced significance (approximately 7.6 sigma) when a more realistic plate-based coverage is considered. This study should be viewed as an initial exploration into the potential of archival photographic surveys to reveal transient phenomena, and we hope it motivates more systematic searches across historical data sets.
- 1Five candidate alignments of multiple simultaneous transients were identified in pre-Sputnik POSS-I plates, with the most statistically significant case reaching approximately 3.9 sigma significance, suggesting a non-random origin.
- 2A highly significant deficit (~22 sigma using hemispheric coverage, ~7.6 sigma using plate-based coverage) of POSS-I transients was found within Earth's umbral shadow at 42,164 km altitude, consistent with a solar reflection origin and inconsistent with photographic plate defects.
- 3The most statistically significant candidate alignment (Candidate 5) occurred on 1952 July 27, coinciding with the second weekend of the Washington D.C. UFO flap, while Candidate 1 occurred within a day of the peak of the 1954 UFO wave.
- 4Simulations using five distinct 3D object geometries (sphere, polyhedron, cone, double pyramid, two-panel structure) demonstrate that slowly spinning or precessing reflective objects in geosynchronous orbit can plausibly reproduce the observed glinting patterns.
- 5An estimated surface number density of approximately 2.0 x 10^-6 km^-2 for reflective objects near geosynchronous orbit was derived from the transient detection rate, with roughly one-third of all VASCO transients attributed to solar reflections from such objects.
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