A Transiting Giant on a 7.7-Year Orbit Revealed by TTVs in the TOI-201 System

Abstract

We report the detection and characterization of TOI-201 c, a long-period transiting companion to the warm Jupiter TOI-201 b. Its presence was first inferred from high-amplitude transit timing variations (TTVs) in TOI-201 b, pointing to a massive outer body on a $7.7_{-0.6}^{+1.0}$-year eccentric orbit. This prediction was confirmed when TESS observed a transit of TOI-201 c, precisely constraining its orbital geometry. A joint fit to TTVs, transit photometry, and archival radial velocities yields a mass of $14.2_{-1.2}^{+1.0}$ $M_{\mathrm{Jup}}$ and an eccentricity of $0.643_{-0.021}^{+0.009}$. The mutual inclination between planets b and c is $2.9_{-4.4}^{+4.8}$ degrees, indicating a nearly coplanar architecture. Long-term numerical integrations confirm dynamical stability over gigayear timescales and predict that transits of TOI-201 b will cease within a few thousand years. TOI-201 c ranks among the longest-period transiting planets with well-constrained properties. Its detection via TTVs, followed by a confirmed transit, represents a rare observational sequence and highlights the power of TTVs and photometric monitoring to uncover distant companions. The TOI-201 system offers a valuable laboratory for testing models of giant planet formation, migration, and secular evolution in multi-planet systems.

Accepted for publication in ApJL on 2025-07-14, submitted on 2025-06-23

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Cited by in corpus (2)

• Uncovering the Rapidly Evolving Orbits of the Dynamic TOI-201 System
• A distant brown dwarf coplanar to a warm Jupiter and a hot super-Earth