Kavli Affiliate: Andrew Vanderburg
| First 5 Authors: Mary Anne Limbach, Johanna M. Vos, Andrew Vanderburg, Fei Dai,
| Summary:
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<$0.35 (95% confidence) and, if none of the detected outlier signals are
real, the occurrence rate of terrestrial ($sim$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.
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