Helium escape signatures are generally strongest during younger ages but this age dependence is lost in the diversity of observed exoplanets

Abstract

Highly irradiated exoplanets undergo extreme hydrodynamic atmospheric escape, due to their high level of received XUV flux. Over their lifetime, this escape varies significantly, making evolution studies essential for interpreting the growing number of observations of escaping planetary atmospheres. In a previous work, we modelled this evolving escape, alongside one of its observable tracers, the helium triplet transit signature at 1083nm. Using hydrodynamic and ray-tracing models, we demonstrated that atmospheric escape and the corresponding He 1083nm signature are stronger at younger ages, for a 0.3$M_{\text{J}}$ gas-giant. Yet, the current literature includes several young (<1Gyr) planets with weak or non-detections in He 1083nm. To understand this apparent discrepancy, we now perform detailed modelling for many of these systems. The resulting He 1083nm predictions align relatively well with the observations. From our two studies, we conclude that for any given planet, stronger atmospheric escape during younger ages produces deeper He 1083nm absorption. However, for a population of exoplanets, the relation between younger ages and stronger He absorptions is lost to the broad diversity of their various other system parameters. Accordingly, for the current sample of young, 1083nm-observed exoplanets, alternative trends take precedence. One such trend is that planets with deeper geometrical transits exhibit more favourable detections. Our modelling also agrees with the strong empirical trend in the literature between $EW\cdot R_{\ast }^2$ and $F_{\text{xuv}}\cdot R_{\text{pl}}^2/{\Phi }_g$. Additionally, we show that the coupling between the lower and upper atmospheres is necessary for a robust prediction of the 1083nm signature.

arXiv comment14 pages, 8 figures (includes 3 in the appendix), 6 tables (2 in appendix). Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal

References in corpus (59)

• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Kepler planets: a tale of evaporation
• Theoretical Transmission Spectra During Extrasolar Giant Planet Transits
• The evaporation valley in the Kepler planets
• Atmospheric Escape from Hot Jupiters
• Probabilistic Forecasting of the Masses and Radii of Other Worlds
• On the radiative equilibrium of irradiated planetary atmospheres
• Stellar magnetism: empirical trends with age and rotation
• Measured Mass Loss Rates of Solar-like Stars as a Function of Age and Activity
• The MUSCLES Treasury Survey I: Motivation and Overview
• How Thermal Evolution and Mass Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond
• Helium in the eroding atmosphere of an exoplanet
• The Interior Structure, Composition, and Evolution of Giant Planets
• Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation
• Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b
• The MUSCLES Treasury Survey II: Intrinsic Lyman Alpha and Extreme Ultraviolet Spectra of K and M Dwarfs with Exoplanets
• Probabilistic Mass-Radius Relationship for Sub-Neptune-Sized Planets
• The active lives of stars: a complete description of rotation and XUV evolution of F, G, K, and M dwarfs
• Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet
• The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical-dynamical model of the thermosphere
• A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium
• The MUSCLES Treasury Survey III: X-ray to Infrared Spectra of 11 M and K Stars Hosting Planets
• Simulating the escaping atmospheres of hot gas planets in the solar neighborhood
• A non-grey analytical model for irradiated atmospheres. I: Derivation
• A grid of upper atmosphere models for 1--40 MEARTH planets: application to CoRoT-7 b and HD219134 b,c
• The evolution of the solar wind
• Aeronomical constraints to the minimum mass and maximum radius of hot low-mass planets
• New reaction rates for improved primordial D/H calculation and the cosmic evolution of deuterium
• Modelling the He I triplet absorption at 10830 Angstroms in the atmosphere of HD 209458 b
• The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation
• Detection of Atmospheric Escape from Four Young Mini Neptunes
• Stellar wind effects on the atmospheres of close-in giants: a possible reduction in escape instead of increased erosion
• p-winds: an open-source Python code to model planetary outflows and upper atmospheres
• Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune
• X-ray irradiation and evaporation of the four young planets around V1298 Tau
• Evolution of atmospheric escape in close-in giant planets and their associated Ly$\alpha$ and H$\alpha$ transit predictions
• Irradiation-driven escape of primordial planetary atmospheres I. The ATES photoionization hydrodynamics code
• TPCI: The PLUTO-CLOUDY Interface
• Effects of the stellar wind on the Ly-alpha transit of close-in planets
• Modelling the He I triplet absorption at 10830 Angstroms in the atmospheres of HD 189733 b and GJ 3470 b
• Keck/NIRSPEC studies of He I in the atmospheres of two inflated hot gas giants orbiting K dwarfs: WASP-52b and WASP-177b
• The Effects of Magnetic Fields on Observational Signatures of Atmospheric Escape in Exoplanets: Double Tail Structures
• Zodiacal Exoplanets in Time. X. The Orbit and Atmosphere of the Young "Neptune Desert"-Dwelling Planet K2-100b
• Homogeneous search for helium in the atmosphere of 11 gas giant exoplanets with SPIRou
• The MOPYS project: A survey of 70 planets in search of extended He I and H atmospheres. No evidence of enhanced evaporation in young planets
• The MUSCLES Extension for Atmospheric and Transmission Spectroscopy: UV and X-ray Host-star Observations for JWST ERS & GTO Targets
• Multi-wavelength variability of the young solar analog iota Hor. X-ray cycle, star spots, flares, and UV emission
• Using helium 10830 Å transits to constrain planetary magnetic fields
• Helium Enhanced Planets Along the Upper Edge of the Radius Valley
• Connection between planetary He I $\lambda$10830 Å absorption and extreme-ultraviolet emission of planet-host stars
• Modeling H$\alpha$ and He 10830 transmission spectrum of WASP-52b
• Confirmation of an He I evaporating atmosphere around the 650-Myr-old sub-Neptune HD235088 b (TOI-1430 b) with CARMENES
• A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654
• Helium in Exoplanet Exospheres: Orbital and Stellar Influences
• Hyades Member K2-136c: The Smallest Planet in an Open Cluster with a Precisely Measured Mass
• Magnetic Field Evolution of Hot Exoplanets
• Evolution of helium triplet transits of close-in gas giants orbiting K-dwarfs
• Atmospheric escape in hot Jupiters under sub-Alfvénic interactions
• GIARPS: the unique VIS-NIR high precision radial velocity facility in this world

Cited by in corpus (1)

• The effects of stellar activity cycles on planetary atmospheric escape and the HeI 1083nm transit signature