Cronomoons: origin, dynamics, and light-curve features of ringed exomoons

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.

The Dynamics of Co-orbital Giant Exomoons -- Applications for the Kepler-1625 b and Kepler-1708 b Satellite Systems

“…In the same work, the author refined the semimajor axis of the satellite, also varying from one data reduction to another, 45 +10 −5 , 36 +10 −13 , and 42 +7 −4 Rp for linear, quadratic, and exponential detrending, respectively. Because of these uncertainties, many theoretical studies adopted the canonical value of 40 Rp for the semimajor axis of the satellite (Hamers & Portegies Zwart 2018;Moraes & Vieira Neto 2020;Moraes et al 2022;Sucerquia et al 2022), which agrees with the prediction given by Martin et al (2019). However, other authors used different values for the planet-satellite separation (Tokadjian & Piro 2022).…”

The bright side of the light curve: a general photometric model of non-transiting exorings

“…Exomoons could also be included (Moskovitz et al, 2009) with the corresponding algorithms to calculate their shadows on the host planet and the ring, and their mutual shine. Even ringed moons or cronomoons (Sucerquia et al, 2022) could be simulated using the spangles approximation. More interestingly, and probably more general in scope, is the possibility to include circumsecondary discs and sub-stellar companions (van Dam et al, 2020;Matthews et al, 2021).…”

“…Here, we restrict the problem to a system composed of a single star and one (or several) ringed planets. Including other objects such as stellar companions, circumstellar discs, moons, and even ringed-moons (cronomoons; Sucerquia et al 2022) will be the goal of future improvements of this model. Still, since the model is modular (as demonstrated below), other objects, effects, and physical phenomena can easily be incorporated (see section 6).…”

The Dynamical Viability of an Extended Jupiter Ring System

“…However, as described in Section 2, particles beyond the fluid body Roche limit may also coalesce into moons on relatively short timescales, and the diversity of eccentricities exhibited in the bottom panel of Figure 3 for many of the surviving particles supports this possible outcome. Another source of particle loss can be capture by the Galilean moons, forming circumsatellite rings (Sucerquia et al 2021). Overall, the Galilean moons carve a substantial area of instability into the region around Jupiter that may only allow relatively short-lived ring systems to coexist with the orbital architectures.…”