Abstract

Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally-driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/non-rocky transition in period-radius space. Here we present the confirmation of TOI-1235 b (P=3.44P=3.44 days, rp=1.7380.076+0.087r_p=1.738^{+0.087}_{-0.076} R_{\oplus}), a planet whose size and period are intermediate between the competing model predictions, thus making the system an important test case for emergence models of the rocky/non-rocky transition around early M dwarfs (Rs=0.630±0.015R_s=0.630\pm 0.015 R_{\odot}, Ms=0.640±0.016M_s=0.640\pm 0.016 M_{\odot}). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and a set of 38 precise radial-velocities from HARPS-N and HIRES. We measure a planet mass of 6.910.85+0.756.91^{+0.75}_{-0.85} M_{\oplus} which implies an iron core mass fraction of 2012+1520^{+15}_{-12}% in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like and we constrain a H/He envelope mass fraction to be <0.5<0.5% at 90% confidence. Our results are consistent with model predictions from thermally-driven atmospheric mass loss but not with gas-poor formation, which suggests that the former class of processes remain efficient at sculpting close-in planets around early M dwarfs. Our RV analysis also reveals a strong periodicity close to the first harmonic of the photometrically-determined stellar rotation period that we treat as stellar activity, despite other lines of evidence favoring a planetary origin (P=21.80.8+0.9P=21.8^{+0.9}_{-0.8} days, mpsini=13.05.3+3.8m_p\sin{i}=13.0^{+3.8}_{-5.3} M_{\oplus}) that cannot be firmly ruled out by our data

    Similar works

    Available Versions