Direct Imaging Constraints on Binary Planets and Exomoons around Epsilon Indi A b

Epsilon Indi A b (hereafter Eps Ind A b) is a directly imaged ∼6 M Jup exoplanet orbiting a nearby (3.6 pc) K dwarf at ∼30 au. We analyze archival JWST/MIRI 15 μ m coronagraphic imaging of this planet to search for directly imaged satellites orbiting Eps Ind A b. Within the planet’s Hill sphere (radius R H ≈ 2.3 au or 1.3 λ / D ), we compare single and double point-spread-function (PSF) models using Bayesian evidence. We find that a double-PSF (binary planet) fit is preferred. This apparent preference can most plausibly be explained by systematics, although follow-up observations would be required to fully rule out a binary planet interpretation. We construct a contrast curve of the exoplanet after removing this feature, demonstrating sensitivity to companions as faint as 0.03× the F1550C flux of Eps Ind A b (equivalent to T = 130 K, 1.3 M Jup ) at large separations (> 2 au). We also demonstrate sensitivity to brighter companions 0.2× the F1550C flux of Eps Ind A b (equivalent to T = 180 K, 2.5 M Jup ) down to separations of 0.52 au (1.3 pixels; 0.29 λ / D ; 144 mas). This study demonstrates that JWST/MIRI can directly detect exomoons or binary planets inside the Hill sphere of directly imaged exoplanets orbiting neighboring stars.