Planetary Reflex Motion from Exomoons: Radial Velocity and Astrometric Budgets

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 rv_earthmoon_jupiter_m_s = 34.5; astrometry_earthmoon_jupiter_uas = 2.20; rv_ganymede_m_s = 0.86; rv_earth_moon_m_s = 12.491. Every moon makes its planet wobble. The planet's reflex motion about the planet-moon barycentre is a velocity signal for a spectrograph watching the planet's own light, or for reflected-light observations, and an angular signal for an astrometer watching the planet's position. As direct imaging begins to deliver spectra and positions of giant planets, this wobble becomes a practical detection budg 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.