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Harvard ADS: Occurrence Rates of Exosatellites Orbiting 3-30M_{\rm Jup} Hosts from 44 Spitzer Light Curves

Paper abstract: We conduct a comprehensive search for transiting exomoons and exosatellites within 44 archival Spitzer light curves of 32 substellar worlds with estimated masses ranging between 3-30M_{\rm Jup}. This sample's median host mass is 16M_{\rm Jup}, inclusive of 14 planetary-mass objects, among which one is a wide-orbit exoplanet. We search the light curves for exosatellite signatures and implement a transit injection-recovery test, illustrating our survey's capability to detect >0.7R_{\oplus} exosatellites. Our findings reveal no substantial (>5\sigma) evidence for individual transit events. However, an unusual fraction of light curves favor the transit model at the 2-3\sigma significance level, with fitted transit depths consistent with terrestrial-sized (0.7-1.6R_{\oplus}) bodies. Comparatively, fewer than 2.2% of randomly generated normal distributions from an equivalent sample size exhibit a similar prevalence of outliers. Should one or two of these outliers represent a real exosatellite transit, it would imply an occurrence rate of \eta = 0.61^{+0.49}_{-0.34} short-period terrestrial exosatellites per system, consistent with the known occurrences rates for both solar system moons and mid M-dwarf exoplanets. We explore alternative astrophysical interpretations for these outliers, underscoring that transits are not the only plausible explanation. For orbital periods <0.8 days, the typical duration of the light curves, we constrain the occurrence rate of sub-Neptunes to \eta<0.35 (95% confidence) and, if none of the detected outlier signals are real, the occurrence rate of terrestrial (~Earth-sized) exosatellites to \eta<0.51 (95% confidence). Forthcoming JWST observations of substellar light curves will enable detection of sub-Io-sized exosatellites, allowing for much stronger constraints on this exosatellite population.