New paper: evaporation of three young planets in the K2-198 system ?>

New paper: evaporation of three young planets in the K2-198 system

The latest paper of my recently graduated PhD student Laura Ketzer is now in print – and as a side note, an all-female author list spanning two different research groups at the AIP:

Plot of LX/Lbol as a function of Rossby number for all stars in the sample by Wright et al. (2011a) with measured rotation periods. Field stars are marked as grey circles, while cluster stars with ages below ∼1 Gyr are shown in five different-coloured age bins. The location of K2-198, which is marked with a yellow star, indicates that the star has already dropped out of the saturated regime and concurs with an age between ∼150 and 600 Myr. (from Ketzer et al. 2024)

Three young planets around the K-dwarf K2-198: high-energy environment, evaporation history, and expected future

Ketzer, L.; Poppenhaeger, K.; Baratella, M.; Ilin, E., Monthly Notices of the Royal Astronomical Society, Volume 527, Issue 1, pp.374-385 (2024)

Planets orbiting young stars are thought to experience atmospheric evaporation as a result of the host stars’ high-magnetic activity. We study the evaporation history and expected future of the three known transiting exoplanets in the young multiplanet system K2-198. Based on spectroscopic and photometric measurements, we estimate an age of the K-dwarf host star between 200 and 500 Myr, and calculate the high-energy environment of these planets using eROSITA X-ray measurements. We find that the innermost planet K2-198c has likely lost its primordial envelope within the first few 10s of Myr regardless of the age at which the star drops out of the saturated X-ray regime. For the two outer planets, a range of initial envelope mass fractions is possible, depending on the not-yet-measured planetary mass and the stars’ spin-down history. Regarding the future of the system, we find that the outermost planet K2-198b is stable against photoevaporation for a wide range of planetary masses, while the middle planet K2-198d is only able to retain an atmosphere for a mass range between ~7 and 18 M⊕. Lower mass planets are too susceptible to mass-loss, and a very thin present-day envelope for higher mass planets is easily lost with the estimated mass-loss rates. Our results support the idea that all three planets started out above the radius valley in the (sub-)Neptune regime and were then transformed into their current states by atmospheric evaporation, but also stress the importance of measuring planetary masses for (young) multiplanet systems before conducting more detailed photoevaporation simulations.

Comments are closed.