Those weird Kuiper Belt orbits scream there’s a hidden Planet Nine—5–10× Earth’s mass, ~600 AU out, doing a 10k–20k‑year lap. Pluto‑killer Mike Brown and Konstantin Batygin built the case, and with only 20–30% of its sky patch searched, the Vera Rubin Observatory could finally catch this mini‑Neptune hiding in the Milky Way’s glare.