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arXiv · 2108.08323

On the Detection of Exomoons Transiting Isolated Planetary-Mass Objects

Mary Anne Limbach·Johanna M. Vos·Joshua N. Winn·Rene Heller·Jeffrey C. Mason·Adam C. Schneider·Fei Dai
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Abstract

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. 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 forecasted noise levels to allow for the detection of an Io-like or Titan-like moon. 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$R_\oplus$ 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.

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Mary Anne Limbach, Johanna M. Vos, Joshua N. Winn, Rene Heller, Jeffrey C. Mason, Adam C. Schneider, Fei Dai. 2021-08-18. On the Detection of Exomoons Transiting Isolated Planetary-Mass Objects. https://doi.org/10.3847/2041-8213%2Fac1e2d

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