A Self-Gravitating Exoring Around J1407b and Implications for In-Situ Exomoon Formation

Abstract

We perform simulations of the M⊕ self-gravitating exoring thought to orbit the large exoplanet J1407b. We use a mass of MJ1407b=20MJ (which is close to the revised upper limit) and a semi-major axis of a=5AU, equating to an orbital period of ∼11yrs about the primary. As J1407b is expected to have a high eccentricity, we test eight different models: where e = 0.2, 0.4, 0.6 and 0.8 in both the prograde and retrograde configurations. All prograde models show a strongly perturbed ring within the first orbit. As expected, the retrograde rings demonstrate a higher degree of stability, with the lower eccentricity models (e = 0.2 and 0.4) able to survive multiple orbits. However, even the higher eccentricity (e = 0.6 and 0.8) retrograde models quickly result in the loss of the ring after 200 years. Excitation of eccentricities in all retrograde rings are stable to gravitational collapse. When assuming the most recent mass estimate of MJ1407b=20MJ the ring is unfavourable to the accretion of moons when J1407b is on an elliptical orbit. An interesting consequence of the strong perturbation for one model (retrograde and e = 0.6) during the first close passage is a transient gap located at 0.4AU. This is the same location as the inferred gap from the single transit in 2007 and does not require a nearby exomoon.

Exomoon Phase Curves: Toroidal Exosphere Simulations of Exo‐Ios Orbiting 8 Exoplanets in Alkali Spectroscopy

“…In 2007, the ∼20 M J companion 1SWASP J1407 b was observed to exhibit multiple and sporadic transits in continuum light, believed to be due to a large and extended ( a ≳ AU) exoring system fueled by exomoons (Kenworthy & Mamajek, 2015; Mamajek et al., 2012). Upon simulating moonlet formation and subsequent evolution with several eccentricities, it has recently been determined that the exoplanet may rather be a free‐floating object nevertheless with an exoring‐exomoon system (Sutton et al., 2022). The search for exomoons therefore has an inextricable avenue linked to exorings.…”