Is there a background population of high-albedo objects in geosynchronous orbits around Earth? (2204.06091v1)

Abstract: Old, digitized astronomical images taken before the human spacefaring age offer a unique view of the sky devoid of known artificial satellites. In this paper, we have carried out the first optical searches ever for non-terrestrial artifacts near the Earth following the method proposed in Villarroel et al. (2022). We use images contained in the First Palomar Sky Survey to search for simultaneous (during a plate exposure time) transients that in addition to being point-like, are aligned. We provide a shortlist of the most promising candidates of aligned transients, that must be examined with the help of a microscope to separate celestial sources from plate defects with coincidentally star-like brightness profiles. We further explore one possible, but not unique, interpretation in terms of fast reflections off high-albedo objects in geosynchronous orbits around Earth. If a future study rules out each multiple transient candidate, the estimated surface density becomes an upper limit of $<10^{-9}$ objects km$^{-2}$ non-terrestrial artifacts in geosynchronous orbits around Earth. Finally, we conclude that observations and analysis of multiple, simultaneously appearing and vanishing light sources on the sky merit serious further attention, regardless of their origin.

• The paper identifies transient alignments in historical POSS-I images consistent with reflections from high-albedo surfaces in GEO.
• The methodology statistically filters 83 candidate events to a shortlist with significance up to 4 sigma, reducing potential photographic artifacts.
• Results suggest an event rate of 0.27 per hour per sky and an upper limit of 3.8×10⁻⁹ objects/km², highlighting the need for further direct plate analysis and modern surveys.

Analysis of High-Albedo Objects in Geosynchronous Orbits

The paper "Is there a background population of high-albedo objects in geosynchronous orbits around Earth?" authored by Villarroel et al. presents an investigation aimed at identifying high-albedo objects in geosynchronous orbits (GEO) around the Earth by analyzing historical astronomical data. This paper utilizes images from the First Palomar Sky Survey (POSS-I) to search for transient phenomena that might indicate reflections from non-terrestrial artifacts (NTAs), potentially offering insights into unexplored aspects of near-Earth space.

Methodology and Data Analysis

The authors conducted a first-ever systematic optical search for NTAs near Earth, focusing on the detection of transients that align in a way consistent with reflections off flat, high-albedo surfaces in GEO. By utilizing the digitalized records from POSS-I, they sought simultaneous transients aligning linearly during a single exposure period. This method counteracts the sporadic nature of transient events arising from random natural causes or photographic plate defects, leveraging the fact that such alignments are statistically improbable without an underlying cause.

The paper revealed 83 candidate alignments of transients in the northern hemisphere, reducing them through scrutiny to a shortlist of the most promising candidates. These alignments could suggest reflections from complex geometrical structures, potentially spinning or precessing in orbit, which possess flat reflective surfaces capable of glinting under specific conditions.

Results and Implications

The paper derived an estimated detection rate for these hypothetical objects as approximately 0.27 events per hour per sky, with an upper limit on their surface density calculated as less than $3.8 \times 10^{-9}$ objects per square kilometer at GEO altitudes. Despite the low probability of coincidental alignment in an individual image, differentiating genuine phenomena from artifacts inherent to the historical photographic plates remains pivotal.

Of the inspected alignments, some exhibited statistical significance, reaching up to 4 sigma levels, which underlines the potential for discovering non-random, aligned transient glints. However, due to the limitations of second-hand image analysis and potential artifacts within the photographic plates, the paper emphasizes the necessity of further examination with direct access to the plates.

Theoretical and Practical Implications

Conceptually, if these aligned transients are indeed reflections from NTAs, it could open an avenue for investigating various poorly understood domains, particularly concerning the distribution and nature of artificial objects within geosynchronous space. This research adds to the broader search and paper of potential non-terrestrial technology, integrating into fields like SETI and space archaeology.

The analysis underscores the importance of observational heritage from the pre-satellite era, where photographic plates provide a unique opportunity to assess celestial changes absent of modern satellite interference. Future investigations can leverage digital sky surveys and modern astronomical instruments to refine searches for aligned-transient events, possibly uncovering further insights.

Future Directions

The logical progression from this research involves scrutinizing the highlighted candidates on their original plates under microscopes, ruling out the possibility of plate defects. Furthermore, expanding the dataset with other historical sky surveys will increase statistical power, potentially yielding more credible candidates.

Simultaneously, modern telescopic surveys with frequent revisits and precise instrumentation, like the Vera C. Rubin Observatory, could be utilized to monitor and validate similar transient alignments. The hypothesis regarding background objects in GEO could be decisively tested through dedicated observation campaigns of the equatorial belt, with extended monitoring of alignment patterns in what is now a congested space with both active satellites and debris.

In conclusion, the paper by Villarroel et al. navigates through a delicate exploration of high-albedo objects in geosynchronous orbits, suggesting a presence that, while requiring further evidence, intrigues the scientific community with profound implications for space observation and the understanding of near-Earth environs.