Capture Budgets for Exomoons: Binary Exchange and Gas Drag Energy Accounting

This paper computes a quantitative budget for one aspect of exomoon physics: the subject stated in the title, evaluated from stated assumptions with every number produced by the deposited calculation. Headline results are moon_binary_binding_J = 2.83e+27; earth_binary_binding_J = 9.34e+30; triton_analogue_binding_J = 2.24e+25; earth_specific_J_per_kg = 1.56e+06. Not every moon is born around its planet. Triton, orbiting Neptune backwards and tilted, is the standing Solar System proof that capture happens, and the wide, inclined, eccentric moons reported or suspected around giant planets invite the same reading. Capture is an energy problem: a body approaching from heliocentric orbit has positive energy relative to the planet and must shed at least that ex The results are compared with published Solar System values and with the constraints attached to reported exomoon candidates where those apply, and the conditions under which the computed budget would change are stated explicitly. Computed from stated assumptions, not measured.