Earth-Shine–Triggered Outgassing as a Unified Explanation of the Earth Flyby Anomaly: A Single Illumination Threshold Across Seventeen Flybys

Since 1990, several spacecraft have shown unexplained mm/s changes in hyperbolic excess speed during Earth gravity assists, while similar flybys showed none. Hoffmann and Budnik (2026) recently re-analysed Rosetta's 2005 flyby at ESOC. They ruled out ephemeris, gravity-field, relativistic, solar-radiation and albedo-pressure explanations, and proposed that Earth-albedo illumination of cold spacecraft faces triggered outgassing of trapped volatiles. Here that hypothesis is tested across all 17 Earth flybys from Galileo (1990) to JUICE (2026), using public JPL Horizons trajectories. Two empirical regularities are reported. First, every reliable anomaly (Galileo I and II, NEAR, Rosetta I) occurred with the spacecraft sunlit at closest approach, while Juno (2013), the only low-altitude null, passed perigee inside Earth's umbra. Second, the peak Earth radiation (reflected sunlight plus thermal infrared) incident on an Earth-facing surface within ±60 min of perigee separates all four anomalies (304–554 W m⁻²) from all four well-measured nulls (≤269 W m⁻²). The separation holds in all 54 variants of albedo, infrared flux, time window and receiver geometry tested (margin 12–23%), and has a chance probability of 1/70. Water-ice sublimation rises about 2000-fold between 160 and 200 K, and 20–35 g of directed vapour suffices for the observed impulses. This makes a sharp illumination threshold physically natural, and accounts for both the apparent ~2000 km altitude cutoff and the day/night dependence without new physics. Falsifiable predictions are given for flybys already flown but not yet reported (Solar Orbiter 2021, Lucy 2022 and 2024: null), Dawn at Mars (2009: null, versus about +1.8 mm/s for rotation-linked models), JUICE's January 2029 Earth flyby (null, versus −0.93 mm/s from the Anderson formula), and low Venus flybys, where planet-shine exceeds the Earth threshold four- to five-fold.