2019/04/29 by George D. McDonald, Laura Kreidberg, Eric Lopez
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Desert (philosophy) #Exoplanet #Flux (metallurgy) #Photoevaporation #Planet #Planetary system #Population #Stars #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/ab1095
published as ApJ 876, 22 (2019) · 22 pages, 15 figures
openalex publication_date 2019/04/29 · openalex created_date 2019/05/09 · arxiv created 2021/05/01 · arxiv updated 2021/05/04 · openalex updated_date 2026/08/05
Abstract Short-period sub-Neptunes with substantial volatile envelopes are among the most common type of known exoplanets. However, recent studies of the Kepler population have suggested a dearth of sub-Neptunes on highly irradiated orbits, where they are vulnerable to atmospheric photoevaporation. Physically, we expect this “photoevaporation desert” to depend on the total lifetime X-ray and extreme ultraviolet flux, the main drivers of atmospheric escape. In this work, we study the demographics of sub-Neptunes as a function of lifetime exposure to high-energy radiation and host-star mass. We find that for a given present-day insolation, planets orbiting a 0.3 M ⊙ star experience ∼100× more X-ray flux over their lifetimes versus a 1.2 M ⊙ star. Defining the photoevaporation desert as a region consistent with zero occurrence at 2 σ , the onset of the desert happens for integrated X-ray fluxes greater than 1.43 × 10 22 to 8.23 × 10 20 as a function of planetary radii for 1.8–4 R ⊕ . We also compare the location of the photoevaporation desert for different stellar types. We find much greater variability in the desert onset in the bolometric flux space compared to the integrated X-ray flux space, suggestive of photoevaporation driven by steady-state stellar X-ray emissions as the dominant control on desert location. Finally, we report tentative evidence for the sub-Neptune valley, first seen around Sun-like stars, for M&K dwarfs. The discovery of additional planets around low-mass stars from surveys such as the Transiting Exoplanet Survey Satellite mission will enable detailed exploration of these trends.