Orphaned exomoons: Tidal detachment and evaporation following an exoplanet–star collision

Miguel A.S. Martinez*, Nicholas C. Stone, Brian D. Metzger

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Gravitational perturbations on an exoplanet from a massive outer body, such as the Kozai–Lidov mechanism, can pump the exoplanet’s eccentricity up to values that will destroy it via a collision or strong interaction with its parent star. During the final stages of this process, any exomoons orbiting the exoplanet will be detached by the star’s tidal force and placed into orbit around the star. Using ensembles of three- and four-body simulations, we demonstrate that while most of these detached bodies either collide with their star or are ejected from the system, a substantial fraction, ∼ 10 per cent, of such ‘orphaned’ exomoons (with initial properties similar to those of the Galilean satellites in our own Solar system) will outlive their parent exoplanet. The detached exomoons generally orbit inside the ice line, so that strong radiative heating will evaporate any volatile-rich layers, producing a strong outgassing of gas and dust, analogous to a comet’s perihelion passage. Small dust grains ejected from the exomoon may help generate an opaque cloud surrounding the orbiting body but are quickly removed by radiation blow-out. By contrast, larger solid particles inherit the orbital properties of the parent exomoon, feeding an eccentric disc of solids that drains more gradually on to the star via Poynting–Robertson drag, and which could result in longer time-scale dimming of the star. For characteristic exomoon evaporation times of ∼105–106 yr, attenuation of the stellar light arising from one or more out-gassing exomoons provides a promising explanation for both the dipping and secular dimming behaviour observed from KIC 8462852 (Boyajian’s Star).

Original languageAmerican English
Pages (from-to)5119-5135
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - 11 Nov 2019

Bibliographical note

Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.


  • Planets and satellites: dynamical evolution and stability
  • Planets and satellites: general
  • Planet–star interactions
  • Stars: peculiar


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