# A resonant pair of warm giant planets revealed by TESS

## TL;DR

This paper reports the discovery of a pair of transiting giant planets around a dwarf star using TESS data, with evidence of near 2:1 resonance and dynamical mass estimates, highlighting a system similar to Kepler-9.

## Contribution

First detection of a resonant pair of warm giant planets with detailed dynamical mass measurements from TESS photometry.

## Key findings

- Planets have radii of 8.2 and 11.3 Earth radii.
- Mass estimates suggest sub-Kronian and Kronian densities.
- System resembles Kepler-9, indicating a possible formation pathway.

## Abstract

We present the discovery of a pair of transiting giant planets, TOI-216b and c, using four sectors of TESS photometry. TOI-216 is a $0.87 M_{\odot}$ dwarf orbited by two transiters with radii of $8.2 R_{\oplus}$ and $11.3 R_{\oplus}$, and periods of $17.01$d and $34.57$d, respectively. Anti-correlated TTVs are clearly evident indicating that the transiters orbit the same star and interact via a near 2:1 mean motion resonance. By fitting the TTVs with a dynamical model, we infer masses of $26_{-11}^{+24} M_{\oplus}$ and $190_{-80}^{+220} M_{\oplus}$, establishing that the objects are planetary in nature and have likely sub-Kronian and Kronian densities. TOI-216 lies close to the southern ecliptic pole and thus will be observed by TESS throughout the first year, providing an opportunity for continuous dynamical monitoring and considerable refinement of the dynamical masses presented here. TOI-216 closely resembles Kepler-9 in architecture, and we hypothesize that in such systems these Saturn-analogs failed to fully open a gap and thus migrated far deeper into the system before becoming trapped into resonance, which would imply that future detections of new analogs may also have sub-Jupiter masses.