Mapping exoplanets across the Milky Way: A representative transit census of the galactic disk with Rubin

We propose a dedicated survey, beginning after the ten-year LSST completes in 2036, that uses the Vera C. Rubin Observatory to build a census of transiting planets across the Milky Way disk, along lines of sight that Kepler did not observe. The baseline design searches about 55 Galactic-plane fields, chosen from a list of 360 candidates covering 3,600 sq deg, in 30-night campaigns at a 6-minute cadence, and spends the rest of five seasons of telescope time (90% of the total) confirming candidates with targeted transit observations. We simulate the survey from star counts, Kepler-derived occurrence rates, transit geometry, and the LSST photometric error model, and test the period search by injecting planets into simulated campaigns. Of the 117,000 transiting planets in the 360 fields that pass a detectability gate, about 7,000 are recovered at the correct period at a false-discovery rate of 5% in the searched fields (39% complete), and about 8,250 are confirmed by a third transit in the allocation model before recovery losses. The sample is dominated by giant and sub-Saturn planets around K and G dwarfs (98% are at least 4 earth radii) and by periods less than 4 days; The M dwarfs contribute a small sample of 1--4 earth radii planets, and the planets in the Earth-size and habitable-zone are beyond reach. All counts are conditional on Kepler occurrence rates and are upper bounds because blends, stellar variability, and red noise are not modeled. The aim is to measure how planet occurrence varies with Galactic environment, which no existing survey can do.