A Pre-Registered Convergence Test for the Planet Nine Hypothesis Using LSST Data Preview 2

The Planet Nine hypothesis predicts that extreme trans-Neptunian objects (ETNOs) exhibit orbital clustering. Current evidence spans p-values from 7e-5 to 0.18 depending on the choice of bias-correction method. Chen (2026, MNRAS, submitted) proposed a convergence framework: if clustering is real, a single statistical test applied with different survey-weighting schemes should agree with an independent non-parametric reference; if it is noise, they will disagree. LSST Data Preview 2 (DP2), expected mid-2026, provides the first opportunity to test this prediction with an independent dataset. This Research Note pre-registers the analysis protocol before DP2 data become available. I will apply the Rayleigh test in six variants -- one unweighted, four survey-weighted (Pan-STARRS, DES, OSSOS, Kuiper), and one Monte Carlo reference -- to the DP2 ETNO sample and report the full set of p-values, convergence tier, and method correlation matrix, irrespective of outcome. This test provides a critical, independent check on whether the ETNO clustering signal reflects a genuine physical phenomenon or an artifact of heterogeneous survey selection.