Mass estimate for the potential inner planet around Kepler-1625 based on the observed TTV of 73.728 min. The thin pale blue fan around the solid curve shows the 1 σ tolerance fanof ±2.016 min. Values for semimajor axes >0.1 AU are poor approximations and thus shown with a dashed line. Black points show masses and semimajor axes of all planets from exoplanet.eu (as of 26 October 2018) around stars with masses between 0.75 M_⊙ and 1.25 M_⊙. A conservative estimate of a dynamically unstable region for the suspected inner planet, where its Hill sphere would touch the Hill sphere of Kepler-1625 b with an assumed mass of 1 M_Jup, is shaded in pale red. RV amplitudes and minimum orbital inclination with respect to Kepler-1625 b are noted along the curve for the planetary mass estimate.