Transit Ly-$\alpha$ signatures of terrestrial planets in the habitable zones of M dwarfs

Abstract

We modeled the transit signatures in the Lya line of a putative Earth-sized planet orbiting in the HZ of the M dwarf GJ436. We estimated the transit depth in the Lya line for an exo-Earth with three types of atmospheres: a hydrogen-dominated atmosphere, a nitrogen-dominated atmosphere, and a nitrogen-dominated atmosphere with an amount of hydrogen equal to that of the Earth. We calculated the in-transit absorption they would produce in the Lya line. We applied it to the out-of-transit Lya observations of GJ 436 obtained by the HST and compared the calculated in-transit absorption with observational uncertainties to determine if it would be detectable. To validate the model, we also used our method to simulate the deep absorption signature observed during the transit of GJ 436b and showed that our model is capable of reproducing the observations. We used a DSMC code to model the planetary exospheres. The code includes several species and traces neutral particles and ions. At the lower boundary of the DSMC model we assumed an atmosphere density, temperature, and velocity obtained with a hydrodynamic model for the lower atmosphere. We showed that for a small rocky Earth-like planet orbiting in the HZ of GJ436 only the hydrogen-dominated atmosphere is marginally detectable with the STIS/HST. Neither a pure nitrogen atmosphere nor a nitrogen-dominated atmosphere with an Earth-like hydrogen concentration in the upper atmosphere are detectable. We also showed that the Lya observations of GJ436b can be reproduced reasonably well assuming a hydrogen-dominated atmosphere, both in the blue and red wings of the Lya line, which indicates that warm Neptune-like planets are a suitable target for Lya observations. Terrestrial planets can be observed in the Lya line if they orbit very nearby stars, or if several observational visits are available.

17 pages, 12 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (26)

• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• Energetic neutral atoms as the explanation for the high velocity hydrogen around HD 209458b
• Habitable Evaporated Cores: Transforming Mini-Neptunes into Super-Earths in the Habitable Zones of M Dwarfs
• Exoplanet HD 209458b : Evaporation strengthened
• Magnetic moment and plasma environment of HD 209458b as determined from Ly$\alpha$ observations
• Exoplanet HD209458b: inflated hydrogen atmosphere but no sign of evaporation
• The long egress of GJ~436b's giant exosphere
• Heating efficiency in hydrogen-dominated upper atmospheres
• Reconnaissance of the TRAPPIST-1 exoplanet system in the Lyman-$\alpha$ line
• Atmosphere Expansion and Mass Loss of Close-Orbit Giant Exoplanets heated by Stellar XUV. II. Effects of Planetary Magnetic Field, Structuring of inner Magnetosphere
• Aeronomical constraints to the minimum mass and maximum radius of hot low-mass planets
• Magma oceans and enhanced volcanism on TRAPPIST-1 planets due to induction heating
• The Interaction of Venus-like, M-dwarf Planets with the Stellar Wind of Their Host Star
• Exoplanets as probes of the winds of host stars: the case of the M dwarf GJ 436
• Two regimes of interaction of a Hot Jupiter's escaping atmosphere with the stellar wind and generation of energized atomic hydrogen corona
• No hydrogen exosphere detected around the super-Earth HD97658 b
• Extreme hydrodynamic atmospheric loss near the critical thermal escape regime
• Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions
• Ultraviolet C II and Si III Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b
• Solar XUV and ENA-driven water loss from early Venus' steam atmosphere
• Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters
• Stellar wind induced soft X-ray emission from close-in exoplanets

Cited by in corpus (12)

• Atmospheres of Rocky Exoplanets
• Global 3D hydrodynamic modeling of in-transit Lyα absorption of GJ436b
• Hydrodynamic escape of water vapor atmospheres near very active stars
• The fundamentals of Lyman-alpha exoplanet transits
• GJ 436b and the stellar wind interaction: simulations constraints using Ly$\alpha$ and H$\alpha$ transits
• Space Weather-driven Variations in Ly$\alpha$ Absorption Signatures of Exoplanet Atmospheric Escape: MHD Simulations and the Case of AU Mic b
• The Earth-like Galactic cosmic ray intensity in the habitable zone of the M dwarf GJ 436
• Evolution of the Earth's Polar Outflow From Mid-Archean to Present
• Global trends in winds of M dwarf stars
• Galactic cosmic ray propagation through M dwarf planetary systems
• Novel Physics of Escaping Secondary Atmospheres May Shape the Cosmic Shoreline
• Evolution of Earth-like extended exospheres orbiting solar-like stars