Scientific Papers

A glint in the eye: Photographic plate archive searches for non-terrestrial artefacts

Beatriz Villarroel, Lars Mattsson, Hichem Guergouri, Enrique Solano, Stefan Geier, Onyeuwaoma Nnaemeka Dom, Martin J. Ward


In this paper, we present a simple strategy to identify Non-Terrestrial artefacts [NTAs; Haqq-Misra and Kopparapu (2012)] in or near geosynchronous Earth orbits (GEOs). We show that even the small pieces of reflective debris in orbit around the Earth can be identified through searches for multiple transients in old photographic plate material exposed before the launch of first human satellite in 1957. In order to separate between possible false point-like sources on photographic plates from real reflections, we present calculations to quantify the associated probabilities of alignments. We show that in an image with nine “simultaneous transients” at least four or five point sources along a line within a 10*10 arcmin^2 image box are a strong indicator of NTAs, corresponding to significance levels of 2.5 to 3.9σ . This given methodology can then be applied to set an upper limit to the prevalence of NTAs with reflective surfaces in geosynchronous orbits.

An environmental analysis of public UAP sightings and sky view potential

R. M. Medina, S. C. Brewer & S. M. Kirkpatrick


Sightings of unidentified flying objects (UFOs) or unidentified anomalous phenomena (UAP) have been reported throughout history. Given the potential security and safety risks they pose, as well as scientific curiosity, there is increasing interest in understanding what these sighting reports represent. We approach this problem as an important one of the human experience and that can be examined through a geographical lens: what local factors may increase or decrease the number of sighting reports? Using a Bayesian regression method, we test hypotheses based on variables representing sky view potential (light pollution, tree canopy, and cloud cover) and the potential for objects to be present in the sky (aircraft and military installations). The dependent variable includes over 98,000 publicly reported UAP sightings in the conterminous United States during the 20-year period from 2001 to 2020. The model results find credible correlations between variables that suggest people see more “phenomena” when they have more opportunity to. This analysis is one of few investigations of UAP sighting reports at a national scale providing context to help examine individual reports. Given that these objects are labeled unidentifiable in the personal sense, there are many natural and/or human based explanations worth exploring.

Unidentified Aerial Phenomena. Events over Kyiv and New York

Preprint · January 2024

Boris Zhilyaev, Dan Caro

We present observations of objects of the Unidentified Aerial Phenomena (UAP) class in Kyiv and New York. Both events are short-lived, 0.17 and 1.028 seconds. Both objects have large linear dimensions, about 150 meters, and the other is about 100 meters. Both objects have an unprecedentedly high speed, about 120 km/s and the other is about 13 km/s.

Limina - The Journal of UAP Studies- a peer-reviewed journal

Officially published articles are available at Limina's new Scholastica publishing platform, as well as being available on Limina's main website. As the Society for UAP Studies is the publisher of the journal, the Society also houses all content (which links to the articles as published with Scholastica).

A bright triple transient that vanished within 50 minutes

arXiv:2310.09035 [astro-ph.SR]

Enrique Solano, Geoffrey W. Marcy, Beatriz Villarroel, Stefan Geier, Alina Streblyanska, Gianluca Lombardi, Rudolf E. Bär, Vitaly N. Andruk

We report on three optically bright, ~15th mag, point-sources within 10 arcsec of each other that vanished within 1 hour, based on two consecutive exposures at Palomar Observatory on 1952 July 19 (POSS I Red and Blue). The three point-sources have continued to be absent in telescope exposures during 71 years with detection thresholds of ~21st mag. We obtained two deep exposures with the 10.4-m Gran Telescopio Canarias on 25 and 27 April 2023 in r and g-band, both reaching magnitude 25.5 (3-sigma). The three point-sources are still absent, implying they have dimmed by more than 10 magnitudes within an hour. When bright in 1952, the most isolated transient source has a profile nearly the same as comparison stars, implying the sources are sub-arcsec in angular size and they exhibit no elongation due to movement. This triple transient has observed properties similar to other cases where groups of transients ("multiple transients") have appeared and vanished in a small region within a plate exposure. The explanation for these three transients and the previously reported cases remains unclear. Models involving background objects that are optically luminous for less than one hour coupled with foreground gravitational lensing seem plausible. If so, a significant population of massive objects with structure serving as the lenses, to produce three images, are required to explain the hundreds of sub-hour transients.

M. Szydagis, K.H. Knuth, B.W. Kugielsky, C. Levy, J.D. McGowan, M.D. Phelan, G.P. Voorhis Jr


In July 2021, faculty from the UAlbany Department of Physics participated in a week-long field expedition with the organization UAPx to collect data on UAPs in Avalon, California, located on Catalina Island, and nearby. This paper reviews both the hardware and software techniques which this collaboration employed, and contains a frank discussion of the successes and failures, with a section about how to apply lessons learned to future expeditions. Both observable-light and infrared cameras were deployed, as well as sensors for other (non-EM) emissions. A pixel-subtraction method was augmented with other similarly simple methods to provide initial identification of objects in the sky and/or the sea crossing the cameras' fields of view. The first results will be presented based upon approximately one hour in total of triggered visible/night-vision-mode video and over 600 hours of untriggered (far) IR video recorded, as well as 55 hours of (background) radiation measurements. Following multiple explanatory resolutions of several ambiguities that were potentially anomalous at first, we focus on the primary remaining ambiguity captured at approximately 4am Pacific Time on Friday, July 16: a dark spot in the visible/near-IR camera possibly coincident with ionizing radiation that has thus far resisted a prosaic explanation. We conclude with quantitative suggestions for serious researchers in this still-nascent field of hard-science-based UAP studies, with an ultimate goal of identifying UAPs without confirmation bias toward either mundane or speculative conclusions.

Publications concerning UFOs in Ukraine and the former Soviet Union

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

Earth and Planetary Astrophysics:

Submitted on 12 Apr 2022 

Beatriz Villarroel, Enrique Solano, Hichem Guergouri, Alina Streblyanska, Lars Mattsson, Rudolf E. Bär, Jamal Mimouni, Stefan Geier, Alok C. Gupta, Vanessa Okororie, Khaoula Laggoune, Matthew E. Shultz, Robert A. Freitas Jr., Martin J. Ward


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.

Hypersonic Unidentified Aerial Objects

Geoffrey W. Marcy & Beatriz Villarroel -Submitted 8 March 2023 



Recent reports describe observations of unidentified objects of ~10-meter size moving at hypersonic speeds of ~10 km s-1 (Zhilyaev et al. 2022ab). Concern has been raised by Loeb (2022) that such speeds, if true, would have caused a bright optical fireball as are created by incoming meteors. But neither a fireball nor a “meteor trail” was observed, raising doubt about the existence of the claimed hypersonic objects. Here we describe an addendum to Loeb’s paper regarding aircraft engineered with a nanoscale frontal cross-sectional area that drastically reduces the air “plow-through” and energy deposition, thereby minimizing any “meteor trail” as is achieved by stealth drone aircraft. Similarly, spacecraft for interstellar travel benefit from nanoscale frontal cross-sections to minimize the number of impacts by interstellar atoms and dust.

Kyiv astronomer Boris Zhilyaev responds to claims from Avi Loeb and the scientific community that his UFO captures are birds, insects, and artillery with a NEW PAPER and 4 NEW VIDEOS! 

Unidentified aerial phenomena. UAPs over Kyiv 

B.E. Zhilyaev, V. N. Petukhov. DOI:10.13140/RG.2.2.20467.60966 


NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used a meteor station installed in Kyiv. We have identified three groups of objects (1) a group of bright spinning objects, (2) a group of bright structured objects and (3) a group of dark flying objects. Monitoring of the daytime sky led to the detection of bright and dark objects, moving at a speed from about 1M to 16Mand sizes from about 20 to 100 meters. The detection of these objects is an experimental fact. Estimates of their characteristics follow from observational data. The authors do not interpret these objects


Physical Constraints on Unidentified Aerial Phenomena

Abraham (Avi) Loeband Sean M. Kirkpatrick


We derive physical constraints on interpretations of “highly maneuverable” Unidentified Aerial Phenomena (UAP) based on standard physics and known forms of matter and radiation. In particular, we show that the friction of UAP with the surrounding air or water is expected to generate a bright optical fireball, ionization shell and tail - implying radio signatures. The fireball luminosity scales with inferred distance to the 5th power. Radar cross-section scales similarly to meteor head echoes as the square of the effective radius of the sphere surrounding the object, while the radar cross-section of the resulting ionization tail scales linearly with the radius of the ionization cylinder. The lack of all these signatures could imply inaccurate distance measurements (and hence derived velocity) for single site sensors without a range gate capability.

“Down to Earth” Limits on Unidentified Aerial Phenomena 

Abraham Loeb. arXiv:submit/4526621 [Astro-ph.IM] 5 Oct 2022


A recent report by astronomers about Unidentified Aerial Phenomena (UAP) in Ukraine (arXiv:2208.11215) suggests dark phantom objects of size 3–12 meters, moving at speeds of up to 15 km s−1 at a distance of up to 10–12 km with no optical emission. I show that the friction of such objects with the surrounding air would have generated a bright optical fireball. Reducing their inferred distance by a factor of ten is fully consistent with the size and speed of artillery shells. 

Paper examination and analysis by Chris Letho

Kiyv astronomer Boris Zhilyaev responds to claims from debunker Mick West and astrophysicist Avi Loeb that his UFO captures are birds, insects, and artillery. Boris argues his case in two papers. In the video Chris Letho presents and explains the papers.  

Unidentified Aerial Phenomena I. Observations of Events 

Zhilyaev, B.E., Petukhov, V.N. and Reshetnyk, V.M., 2022. Unidentified aerial phenomena I. Observations of events. arXiv preprint arXiv:2208.11215


NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used two meteor stations. Observations were performed with colour video cameras in the daytime sky. We have developed a special observation technique, for detecting and evaluating UAP characteristics. According to our data, there are two types of UAP, which we conventionally call: (1) Cosmics, and (2) Phantoms. We note that Cosmics are luminous objects, brighter than the background of the sky. Phantoms are dark objects, with contrast from several to about 50 per cent. We observe a significant number of objects whose nature is not clear. Flights of single, group and squadrons of the ships were detected, moving at speeds from 3 to 15 degrees per second. Some bright objects exhibit regular brightness variability in the range of 10 - 20 Hz. We use colourimetry methods to determine of distance to objects and evaluate their colour characteristics. Objects RGB colours of the Adobe colour system had converted to the Johnson BVR astronomical colour system using the colour corrections. Phantom shows the colour characteristics inherent in an object with zero albedos. It is a completely black body that does not emit and absorbs all the radiation falling on it. We see an object because it shields radiation due to Rayleigh scattering. An object contrast makes it possible to estimate the distance using colourimetric methods. Phantoms are observed in the troposphere at distances up to 10 - 12 km. We estimate their size from 3 to 12 meters and speeds up to 15 km/s.

Unidentified aerial phenomena II. Evaluation of UAP properties

B.E. Zhilyaev, V.N. Petukhov and V.M. Reshetnyk. 2022. arXiv preprint arXiv:2211.17085 


NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used two meteor stations installed in Kyiv and in the Vinarivka village in the south of the Kyiv region. Two-side monitoring of the daytime sky led to the detection of two luminous objects at an altitude of 620 and 1130 km, moving at a speed of 256 and 78 km/s. Colorimetric analysis showed that the objects are dark: B - V = 1.35, V - R = 0.23. The size of objects is estimated to be more than 100 meters. The detection of these objects is an experimental fact. Estimates of their characteristics follow from observational data. The authors do not interpret these objects. Daytime sky monitoring in Kyiv with multi-color DSLR camera at a rate of 30 frames per second in August and September 2018 and in Vinarivka with a multi-color CMOS camera in October 2022 revealed several cases of dark objects (phantoms). The time of their existence is, as a rule, a fraction of a second. These are oval-shaped objects ranging in size from 20 to 100 meters with speeds from 2 to 30 km/s.

Estimating Flight Characteristics of Anomalous Unidentified Aerial Vehicles

Knuth, K.H., Powell, R.M. and Reali, P.A., 2019. Estimating Flight Characteristics of Anomalous Unidentified Aerial Vehicles. Entropy, 21(10), p.939. 


Several Unidentified Aerial Phenomena (UAP) encountered by military, commercial, and civilian aircraft have been reported to be structured craft that exhibit ‘impossible’ flight characteristics. We consider a handful of well-documented encounters, including the 2004 encounters with the Nimitz Carrier Group off the coast of California, and estimate lower bounds on the accelerations exhibited by the craft during the observed maneuvers. Estimated accelerations range from almost 100g to 1000s of gs with no observed air disturbance, no sonic booms, and no evidence of excessive heat commensurate with even the minimal estimated energies. In accordance with observations, the estimated parameters describing the behavior of these craft are both anomalous and surprising. The extreme estimated flight characteristics reveal that these observations are either fabricated or seriously in error, or that these craft exhibit technology far more advanced than any known craft on Earth. In many cases, the number and quality of witnesses, the variety of roles they played in the encounters, and the equipment used to track and record the craft favor the latter hypothesis that these are indeed technologically advanced craft. The observed flight characteristics of these craft are consistent with the flight characteristics required for interstellar travel, i.e., if these observed accelerations were sustainable in space, then these craft could easily reach relativistic speeds within a matter of minutes to hours and cover interstellar distances in a matter of days to weeks, proper time. 

Improved Instrumental Techniques, Including Isotopic Analysis, Applicable to the Characterization of Unusual Materials with Potential Relevance to Aerospace Forensics

Nolan, G.P., Vallee, J.F., Jiang, S. and Lemke, L.G., 2022. Improved instrumental techniques, including isotopic analysis, applicable to the characterization of unusual materials with potential relevance to aerospace forensics. Progress in Aerospace Sciences, 128, p.100788. 


The problem of precise characterization, analysis, and eventual identification of unknown materials arises in many fields and takes many forms, depending on the nature of the substances under study. In the first part of this paper we review common, modern mass spectrometry techniques applied to such studies. We also give an overview of improvements made to these technologies in recent years by Silicon Valley companies and other teams focused on precise biomedical research dependent upon sensitive techniques, yet applicable to a wide range of non-biological materials. In the second and third parts of the paper we review practical experiences applying these techniques to the simplest case of the characterization of solid materials (as opposed to liquids or gases) and comparing our results with previously undertaken isotopic analysis. In particular, we describe our correlations of that analysis with the patterns described by witnesses in a well-documented, still-unexplained incident, initially thought to be of aerospace origin, which gave rise to the deposition of unknown material, and by the investigators who handled it in the field and the laboratory. The lessons from this specific investigation are applicable to a wider range of issues in reverse engineering of complex, esoteric materials, and aerospace forensics.

Isotope Ratios and Chemical Analysis of the 1957 Brazilian Ubatuba Fragment.

Powell, Robert M.; Swords, Michael D.; Rodeghier, Mark; Budinger, Phyllis. Journal of Scientific Exploration . Spring2022, Vol. 36 Issue 1, p39-48. 10p.  


A sample from the Ubatuba fragment collected in Brazil in 1957 was tested with the intent of examining the isotope ratios of its primary element, magnesium, and the trace elements strontium, barium, copper, and zinc. As background, the history of chemical testing of the Ubatuba fragments during the 1960s-1980s at multiple labs with varying capabilities is reviewed and then the remainder of the paper examines recent tests completed in 2017 and 2018 that for the first time used HR-ICPMS techniques to look at the isotopic ratios of the minor constituents as well as the primary magnesium component of the sample. The magnesium isotope ratios were found to fall within terrestrial limits while the results on the isotope ratios of the trace elements were inconclusive. Recommendations are made for improving the process of examining the trace elements. 

Advanced Space Propulsion Based on Vacuum (Spacetime Metric) Engineering

Harold E. Puthoff, 2012.


A theme that has come to the fore in advanced planning for long-range space exploration is the concept that empty space itself (the quantum vacuum, or spacetime metric) might be engineered so as to provide energy/thrust for future space vehicles. Although far-reaching, such a proposal is solidly grounded in modern physical theory, and therefore the possibility that matter/vacuum interactions might be engineered for space-flight applications is not a priori ruled out. As examples, the current development of theoretical physics addresses such topics as warp drives, traversable wormholes and time machines that provide for such vacuum engineering possibilities. We provide here from a broad perspective the physics and correlates/consequences of the engineering of the spacetime metric.


The materials with negative refractive index (also known as left-handed media, LHM) have attracted a great deal of attention during recent years. However, despite numerous efforts to bring LHMs to optical or even THz domain all modern realizations of these fascinating systems are limited to GHz waveguides ..... In this work we study the imaging properties of these non-magnetic LHMs, and propose their THz realization based on a homogeneous, naturally occurring material.