Context :

Aims : L 98-59 ( TIC 307210830 , TOI-175 ) is a nearby M3 dwarf around which TESS revealed three terrestrial-sized transiting planets ( 0.80 , 1.35 , 1.57 Earth radii ) in a compact configuration with orbital periods shorter than 7.5 days .
Here we aim to measure the masses of the known transiting planets in this system using precise radial velocity ( RV ) measurements taken with the HARPS spectrograph .

Methods : We consider both trained and untrained Gaussian process regression models of stellar activity to simultaneously model the RV data with the planetary signals .
Our RV analysis is then supplemented with dynamical simulations to provide strong constraints on the planets ’ orbital eccentricities by requiring long-term stability .

Results : We measure the planet masses of the two outermost planets to be 2.46 \pm 0.31 and 2.26 \pm 0.50 Earth masses which confirms their bulk terrestrial compositions .
We are able to place an upper limit on the mass of the smallest , innermost planet of < 0.98 Earth masses with 95 % confidence .
Our RV + dynamical stability analysis places strong constraints on the orbital eccentricities and reveals that each planet ’ s orbit likely has e < 0.1 to ensure a dynamically stable system .

Conclusions : The L 98-59 compact system of three likely rocky planets offers a unique laboratory for studies of planet formation , dynamical stability , and comparative atmospheric planetology .
Continued RV monitoring will help refine the characterization of the innermost planet and potentially reveal additional planets in the system at wider separations .