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Journal Article

On the Detection of Exomoons Transiting Isolated Planetary-mass Objects


Heller,  René
Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society;

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Limbach, M. A., Vos, J. M., Winn, J. N., Heller, R., Mason, J. C., Schneider, A. C., et al. (2021). On the Detection of Exomoons Transiting Isolated Planetary-mass Objects. The Astrophysical Journal Letters, 918: L25. doi:10.3847/2041-8213/ac1e2d.

Cite as: https://hdl.handle.net/21.11116/0000-0009-232B-0
All-sky imaging surveys have identified several dozen isolated planetary-mass objects (IPMOs) far away from any star. Here we examine the prospects for detecting transiting moons around these objects. We expect transiting moons to be common, occurring around 10%–15% of IPMOs, given that close-orbiting moons have a high geometric transit probability and are expected to be a common outcome of giant planet formation. The IPMOs offer an advantage over other directly imaged planets in that high-contrast imaging is not necessary to detect the photometric transit signal. For at least 30 (>50%) of the currently known IPMOs, observations of a single transit with the James Webb Space Telescope would have low enough forecast noise levels to allow for the detection of an Io- or Titan-like moon. The intrinsic variability of the IPMOs will be an obstacle. Using archival time-series photometry of IPMOs with the Spitzer Space Telescope as a proof of concept, we found evidence for a fading event of 2MASS J1119–1137 AB that might have been caused by intrinsic variability but is also consistent with a single transit of a habitable-zone 1.7 R⊕ exomoon. Although the interpretation of this particular event is inconclusive, the characteristics of the data and the candidate signal suggest that Earth-sized habitable-zone exomoons around IPMOs are detectable with existing instrumentation.