2025/07/12 by Charles Cadieux, Alexandrine L'Heureux, Cadieux, Charles +27 · 4 voices · 2 citations
#astro-ph.EP
paper · pdf · doi:10.48550/arxiv.2507.09343
The L 98-59 system, identified by TESS in 2019, features three transiting exoplanets in compact orbits of 2.253, 3.691, and 7.451 days around an M3V star, with an outer 12.83-day non-transiting planet confirmed in 2021 using ESPRESSO. The planets exhibit a diverse range of sizes (0.8-1.6 R⊕), masses (0.5-3 M⊕), and likely compositions (Earth-like to possibly water-rich), prompting atmospheric characterization studies with HST and JWST. Here, we analyze 16 new TESS sectors and improve radial velocity (RV) precision of archival ESPRESSO and HARPS data using a line-by-line framework, enabling stellar activity detrending via a novel differential temperature indicator. We refine the radii of L 98-59 b, c, and d to 0.837 ± 0.019 R⊕, 1.329 ± 0.029 R⊕, 1.627 ± 0.041 R⊕, respectively. Combining RVs with transit timing variations (TTV) of L 98-59 c and d from TESS and JWST provides unprecedented constraints on the masses and eccentricities of the planets. We report updated masses of 0.46 ± 0.11 M⊕ for b, 2.00 ± 0.13 M⊕ for c, and 1.64 ± 0.07 M⊕ for d, and a minimum mass of 2.82 ± 0.19 M⊕ for e. We additionally confirm L 98-59 f, a non-transiting super-Earth with a minimal mass of 2.80 ± 0.30 M⊕ on a 23.06-day orbit inside the Habitable Zone. The TTVs of L 98-59 c and d (<3 min, P\rm TTV = 396 days) constrain the eccentricities of all planets to near-circular orbits (e \lesssim 0.04). An internal structure analysis of the transiting planets reveals increasing water-mass fractions (f_\rm H2O) with orbital distance, reaching f_\rm H2O ≈ 0.16 for L 98-59 d. We predict eccentricity-induced tidal heating in L 98-59 b with heat fluxes comparable to those of Io, potentially driving volcanic activity.