On the Detection of Exomoons Transiting Isolated Planetary-mass Objects

Mary Anne Limbach, Johanna M. Vos, Joshua N. Winn, René Heller, Jeffrey C. Mason, Adam C. Schneider, Fei Dai

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


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.

Original languageEnglish (US)
Article numberL25
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Sep 10 2021

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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