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Exomoon Simulations of Toroidal Exospheres

Presentation #222.04 in the session Exoplanets Formation & Evolution (Poster + Lightning Talk)

Published onOct 23, 2023
Exomoon Simulations of Toroidal Exospheres

Toroidal atmospheres and exospheres characterized at exoplanets may be fueled by volcanically-active exomoons, often referred to as exo-Ios. We study the neutral outgassing and volatile evolution of a close-orbiting, evaporating satellite at eight candidate exoplanet-exomoon systems WASP-49, -96, -69, -17 b I, XO-2N b I, HAT-P-1 b I, HD-189733 b II, HD-209458 b I, and the ultra-hot Jupiter systems WASP-76 b I and WASP-121 b I by developing a 3-D test-particle Monte-Carlo simulation, SERPENS. The module is coupled to dishoom, approximating the minimum mass-flux needed to reproduce observations of alkali line profiles identified in dozens of transmission spectra. We focus on neutral sodium, limited by photoionization and radiative effects. By considering Earth-, Io-, and Enceladus-like masses, we systematically simulate the imprint of a non-hydrostatic medium (characteristic of volcanic exospheres) in density and velocity space using a novel Delaunay tessellation field estimator algorithm. Our results demonstrate how exomoons can considerably modulate gas density observations probed near exoplanet transit, depending on the orbital phase of the putative satellite at the time of observation. The density evolution, therefore, manifests on orbital timescales as ‘exomoon phase curves’ from shadow to occultation. We find two regimes of density evolution, characteristic of a: (A) localized cloud and (B) an azimuthally symmetric exoring/torus, degenerate with an exoplanet atmosphere, ranging from 109.5±0.5 cm-2 to 1015±0.25 cm-2 at our leading candidate WASP-69 b I. In certain orbital architectures, the smallest evaporating satellite mass surprisingly generates the brightest sodium signal, fueling optimism for discovering photometrically-indiscernible rocky exomoons. We suggest long baseline monitoring of alkali and SO2 systems in spectroscopy to search for the temporal and spatial variability predicted here.

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