A Response to paper Critical Evaluation of Studies Alleging Evidence for Technosignatures in the POSS1-E Photographic Plates by Watters et al. (2026)

TL;DR

This paper responds to Watters2026's critique of the statistical analyses in Villarroel2025 and Bruehl & Villarroel2025 by arguing that ensemble-level inference does not require object-level validation and that the aggressive 5,399-object subset is inappropriate for testing the Earth-shadow deficit. It defends using a larger ~107,000-transient Palomar POSS-I sample, explaining that the smaller subset was designed for vanishing-star searches and may bias interpretation, while the 107k sample enables detection of subtle alignments and solar-reflection contamination estimates. The authors show the Earth-shadow deficit is highly significant with the full sample ($7.6\sigma$) and persists under sky-coverage comparisons ($22\sigma$), while reduced datasets (e.g., 4,866 transients) are underpowered and lack error propagation. They highlight methodological issues in Watters2026, such as time assignments without the $\cos(Dec)$ correction in horizontal separations and the absence of uncertainty estimates, concluding that the critique does not invalidate the main findings and underscores the need for proper uncertainty treatment and methodological alignment.

Abstract

We respond to the critique by Watters et al. (2026) of the statistical analyses in Villarroel et al. (2025) and Bruehl & Villarroel (2025). We argue that the critique conflates object-level validation with ensemble-level statistical inference and relies on a reduced, heterogeneously filtered subset originally constructed for a different scientific purpose. We further question whether the aggressively filtered subset used in Watters et al. (2026) demonstrates a meaningful improvement in sample purity, given the twenty-fold reduction in sample size. Our simple, visual check does not suggest that it does. The subset further lacks complete temporal information and is seriously statistically underpowered for testing the reported Earth-shadow deficit. We emphasise that the horizontal separation metric used for plate assignment and time reconstruction as in Watters et al. (2026) depends on the inclusion of the cos(Dec) factor to ensure geometric consistency. Any omission would alter plate assignment and inferred observation times. Moreover, the analyses presented in Watters et al. (2026) do not include uncertainty estimates or error propagation, limiting the interpretability of the claimed null results. We conclude that the principal findings reported in Villarroel et al. (2025) and Bruehl & Villarroel (2025) are not invalidated by the analyses presented in Watters et al. (2026).

Figures (2)

• Figure 1: Illustrative histogram of the 107,000 transients. In the last communication between W. Watters and B. Villarroel in July 2025, Watters shared this central figure with above text to express his concern regarding an apparent increase in the number of transients towards the plate edge (see the Acknowledgements in Watters et al. 2026). The photographic plates are $6\times6$ degrees in size, whereas the x-axis of the histogram extends to 10 degrees from the plate centre, and outside the plate edge. This suggests missing a cos(Dec)-correction when calculating the horizontal separation (difference in R.A.). Further, the histogram does not take into account plate overlap regions. The figure serves to illustrate how sensitive the time reconstruction in Watters et al. (2026) is to the adopted horizontal separation estimates and definitions. We thank W. Watters for sharing this figure.
• Figure 2: Histogram with and without cos(Dec)-correction. The left figure (correct) shows a histogram with cos(Dec) correction when calculating the horizontal separations. The right figure shows a histogram without the cos(Dec) correction when calculating the horizontal separations from the plate center. The right distribution looks similar to Watters figure, albeit with narrower bins.