Io Plasma Torus Density and Mass-Loading Budget: Neutral Source Rates Against Juno and Galileo Plasma Measurements

This paper computes a quantitative budget for the magnetosphere of Jupiter from published spacecraft values, using a deliberately transparent calculation whose every step can be checked from the deposited script. The headline results are: source_rate_kg_s = 1e+03; plasma_inventory_kg = 3.46e+09; mean_ion_density_per_m3 = 7.25e+08; peak_electron_density_per_m3 = 3e+09; residence_time_days = 40; torus_volume_m3 = 1.2e+26. The computed mean density sits well below the measured peak, by a factor consistent with the known structure of the torus, in which plasma concentrates near the centrifugal equator and falls off steeply with distance from it. That consistency is the substance of the check: if the source rate or residence time were wrong by an order of magnitude, the mean would collide with either the peak or with densities measured in the torus's outer skirts, and it does neither. The inventory itself, thousands of tonnes of plasma, is the reservoir whose outward transport ultimately supplies Jupiter's auroral and radiation processes. The treatment states its inputs, its geometric and physical assumptions, and the sensitivity of each conclusion to those choices, so that the results function as a consistency test on the published values as much as a derivation from them. Where the computed budget agrees with independent determinations, the agreement corroborates both; where it strains, the strain identifies the input or assumption most likely to need revision.