Exoplanets, -moons, -comets

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

By Keith Cowing

Status Report

astro-ph.EP

April 29, 2026

Filed under astro-ph.EP, astronomy, binary planet, coronagraph, Epsilon Indi A, Epsilon Indi Ab, Exomoon, exoplanet, JWST, K-dwarf

Direct Imaging Constraints on Binary Planets and Exomoons around Epsilon Indi A b — Fits and residuals of stage 3 F1550C data subtracted using the results of PyMultiNest single- and double-PSF fitting. Each panel indicates the 31×31 pixel cropped regions, while the dashed box indicates the 15×15 pixel test region used in fitting. The residuals are significantly reduced when a double-PSF fit is applied. In the left two panels, the injected data are shown, with a black cross and brown circle indicating the fitted locations of the primary and secondary, respectively (using RS-2 as a PSF model). The residuals of these fits are shown in the middle panels. The right panels show the residuals of fits using a synthetic StPSF model; these residuals are visibly larger than those of the reference star model. — astro-ph.EP

Epsilon Indi A b is a directly imaged ∼6M_Jup exoplanet orbiting a nearby (3.6 pc) K-dwarf at ∼30 AU.

We analyze archival JWST/MIRI 15 μm 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 1.3λ/D), we compare single- and double-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, 1.3M_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, 2.5M_Jup) down to separations of 0.52 AU (1.3 pixels; 0.29λ/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.

Matson Garza (1), Mary Anne Limbach (2), Rachel Bowens-Rubin (2 and 3), Matthew De Furio (4), Elisabeth C. Matthews (5), Kyle Franson (6), Sarah C. Millholland (1), Logan A. Pearce (2), Andrew Vanderburg (7) ((1) Department of Physics, Massachusetts Institute of Technology, (2) Department of Astronomy, University of Michigan, (3) Eureka Scientific Inc., (4) Department of Astronomy, The University of Texas at Austin, (5) Max Planck Institute for Astronomy, (6) Department of Astronomy and Astrophysics, The University of California, Santa Cruz, (7) Center for Astrophysics, Harvard & Smithsonian)

Comments: Accepted to AJ, 14 pages with 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2604.23448 [astro-ph.EP] (or arXiv:2604.23448v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.23448
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Submission history
From: Matson Garza
[v1] Sat, 25 Apr 2026 21:33:52 UTC (275 KB)
https://arxiv.org/abs/2604.23448

Astrobiology, exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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