A Compact Multi-Planet System of Three Transiting Giant Planets Around TIC118798035

TL;DR

We report the discovery and detailed characterization of TIC118798035, a solar-type star hosting three transiting warm giant planets. By combining TESS photometry, ground-based transits (OMES600, HATPI), and high-resolution spectroscopy (FEROS, HARPS, ESPRESSO), we perform a self-consistent N-body TTV+RV analysis in Jacobi coordinates to derive precise masses and orbits: $m_p(b)=0.025\,M_J$, $m_p(c)=0.403\,M_J$, $m_p(d)=0.773\,M_J$ with radii $R_b=0.655\,R_J$, $R_c=0.973\,R_J$, $R_d=0.923\,R_J$, and periods $P_b=11.5075$ d, $P_c=22.5644$ d, $P_d=48.9244$ d. The planets lie near first-order period ratios ($P_c/P_b\approx1.96$, $P_d/P_c\approx2.17$) but show no low-order mean-motion resonance, and dynamical integration confirms long-term stability with small mutual inclinations and a low stellar obliquity. Interior modeling reveals bulk metallicities $Z_c=0.15\pm0.03$ and $Z_d=0.22\pm0.05$ (with atmospheric metallicities constrained to <$19.2\times$Solar and <$33.2\times$Solar, respectively), while TIC118798035 b remains compositionally degenerate but likely highly enriched if ice/rock ratios are favorable. The system stands out as a unique testbed for mass–metallicity relations and atmospheric studies, offering a compelling target for JWST to characterize the atmospheres of three transiting giants within a single system.

Abstract

We report the discovery and characterization of three transiting giant planets in the TIC118798035 system. The three planets were identified as transiting candidates from data of the TESS mission, and confirmed with ground-based photometric transit observations along with radial velocity variations obtained with FEROS, HARPS and ESPRESSO. The three planets present transit timing variations (TTVs). We performed a N-body orbital fitting to the TTVs and radial velocities finding that TIC118798035 b is as warm low-density Neptune with a mass of 0.0250$\pm$0.0023 $M_J$, a radius of 0.655$\pm$0.018 $R_J$, and an orbital period of 11.507 d; TIC118798035 c is a warm Saturn with a mass of 0.403$\pm$0.024 $M_J$, a radius of 0.973$\pm$0.023 $R_J$, and an orbital period of 22.564 d; and TIC118798035 d is a warm Jupiter with a mass of 0.773$\pm$0.052 $M_J$, a radius of 0.923$\pm$0.044 $R_J$, and an orbital period of 48.925 d. The bulk metallicities of the three planets don't fully follow the mass-metallicity correlation found for the giant planets of the solar system, which hints at a somewhat different formation history for the planets of the TIC118798035 system. TIC118798035 is the only system having more than two transiting planets larger than 0.5 $R_J$ with a precise orbital and physical characterization, amenable for future atmospheric studies.

Figures (11)

• Figure 1: TESS light curves of TIC118798035 from sectors 13, 39, 66, and 93, from top to bottom. Regions around transits of the candidates $b$, $c$, and $d$ ar marked in red, blue and green, respectively. We also plot the model for the out of transit variations computed with the gaussian process described in Section \ref{['sec:juliet']}
• Figure 2: GLS periodogram generated from the FEROS, HARPS, and ESPRESSO radial velocities of TIC118798035. The horizontal lines correspond to the 10% and 1% false alarm probabilities. The red and blue dashed vertical lines mark the orbital periods of candidates $b$ and $c$, respectively. The green dashed vertical lines mark the possible period aliases of TIC118798035 d based on TESS photometry.
• Figure 4: TESS and ground-based transits of TIC118798035 b centered on the transit time predicted from linear ephemeris. The transit model generated by juliet is also plotted for each transit.
• Figure 5: Same as Figure \ref{['fig:transitsb']}, but for TIC118798035 c.
• Figure 6: Same as Figure \ref{['fig:transitsb']}, but for TIC118798035 d.