Photometric Transit Depth Thresholds for Direct Detection of Exomoon Transits

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 earth_sun_depth_ppm = 84; earth_mdwarf_depth_ppm = 932; moon_sun_depth_ppm = 6.2; ganymede_sun_ppm = 14.3; transits_for_5sigma_earth_sun_30ppm = 3.20. The most direct exomoon signature is the moon's own shadow: an additional shallow dip before, after or within the planet's transit, repeating with the geometry of the system. Its depth is set purely by areas, the square of the moon-to-star radius ratio, so the budget can be written down exactly and compared with the photometric precision of past and present surveys. This paper tabulates that budge 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.