Milky Way–Andromeda Collision Odds Fluctuate as New Data Refine Forecasts

New studies show the forecast of a Milky Way–Andromeda merger is far from settled: a 2025 Nature Astronomy analysis using Hubble and Gaia data suggested roughly 50–50 odds for a merger within the next 10 billion years, while a 2026 follow-up with Gaia-based motions pushed the probability toward about 90% under its preferred model; the results depend on uncertain motions and nearby galaxies (Triangulum and the Large Magellanic Cloud), and they distinguish between a first close approach and a final merger. Precise proper-motion measurements—down to microarcseconds per year—are needed to narrow the forecast.