Cronomoons: origin, dynamics, and light-curve features of ringed exomoons
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Date
2021-12-14
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Abstract
In recent years, technical and theoretical work to detect moons and rings around exoplanets has been attempted. The small
mass/size ratios between moons and planets means this is very challenging, having only one exoplanetary system where spotting
an exomoon might be feasible (i.e. Kepler-1625b i). In this work, we study the dynamical evolution of ringed exomoons, dubbed
cronomoons after their similarity with Cronus (Greek for Saturn), and after Chronos (the epitome of time), following the Transit
Timing Variations (TTV) and Transit Duration Variation (TDV) that they produce on their host planet. Cronomoons have
extended systems of rings that make them appear bigger than they actually are when transiting in front of their host star. We
explore different possible scenarios that could lead to the formation of such circumsatellital rings, and through the study of the
dynamical/thermodynamic stability and lifespan of their dust and ice ring particles, we found that an isolated cronomoon can
survive for time-scales long enough to be detected and followed up. If these objects exist, cronomoons’ rings will exhibit gaps
similar to Saturn’s Cassini Division and analogous to the asteroid belt’s Kirkwood gaps, but instead raised due to resonances
induced by the host planet. Finally, we analyse the case of Kepler-1625b i under the scope of this work, finding that the
controversial giant moon could instead be an Earth-mass cronomoon. From a theoretical perspective, this scenario can contribute
to a better interpretation of the underlying phenomenology in current and future observations.
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Keywords
Planets and satellites: rings, Techniques: photometric, Methods: analytical, Techniques: photometric, Planets and satellites: dynamical evolution and stability, Planets and satellites: detection