Lightning-induced chemistry on tidally-locked Earth-like exoplanets

Abstract

Determining the habitability and interpreting atmospheric spectra of exoplanets requires understanding their atmospheric physics and chemistry. We use a 3-D Coupled Climate-Chemistry Model, the Met Office Unified Model with the UK Chemistry and Aerosols framework, to study the emergence of lightning and its chemical impact on tidally-locked Earth-like exoplanets. We simulate the atmosphere of Proxima Centauri b orbiting in the Habitable Zone of its M-dwarf star, but the results apply to similar M-dwarf orbiting planets. Our chemical network includes the Chapman ozone reactions and hydrogen oxide (HO${}_{\mathrm{x}}$=H+OH+HO${}_2$) and nitrogen oxide (NO${}_{\mathrm{x}}$=NO+NO${}_2$) catalytic cycles. We find that photochemistry driven by stellar radiation (177-850 nm) supports a global ozone layer between 20-50 km. We parameterise lightning flashes as a function of cloud-top height and the resulting production of nitric oxide (NO) from the thermal decomposition of N${}_2$ and O${}_2$. Rapid dayside convection over and around the substellar point results in lightning flash rates of up to 0.16 flashes km${}^{-2}$yr${}^{-1}$, enriching the dayside atmosphere below altitudes of 20 km in NO${}_{\mathrm{x}}$. Changes in dayside ozone are determined mainly by UV irradiance and the HO${}_{\mathrm{x}}$ catalytic cycle. ~45% of the planetary dayside surface remains at habitable temperatures (T${}_{\mathrm{surf}}$>273.15 K) and the ozone layer reduces surface UV radiation levels to 15%. Dayside-nightside thermal gradients result in strong winds that subsequently advect NO${}_{\mathrm{x}}$ towards the nightside, where the absence of photochemistry allows NO${}_{\mathrm{x}}$ chemistry to involve reservoir species. Our study also emphasizes the need for accurate UV stellar spectra to understand the atmospheric chemistry of exoplanets.

20 pages, 14 figures, accepted for publication in MNRAS

References in corpus (29)

• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
• The habitability of Proxima Centauri b II. Possible climates and Observability
• The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• Tidal Locking of Habitable Exoplanets
• Abiotic Ozone and Oxygen in Atmospheres Similar to Prebiotic Earth
• Atmospheric dynamics of Earth-like tidally locked aquaplanets
• The Effects of Consistent Chemical Kinetics Calculations on the Pressure-Temperature Profiles and Emission Spectra of Hot Jupiters
• The Space Weather of Proxima Centauri b
• Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model
• The rotational and divergent components of atmospheric circulation on tidally locked planets
• A review of possible planetary atmospheres in the TRAPPIST-1 system
• Atmospheric electrification in the Solar System
• Atmospheric convection plays a key role in the climate of tidally-locked terrestrial exoplanets: insights from high-resolution simulations
• Connecting the dots: A versatile model for the atmospheres of tidally locked Super-Earths
• Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology
• A Low-order Model of Water Vapor, Clouds, and Thermal Emission for Tidally Locked Terrestrial Planets
• Stratosphere circulation on tidally locked ExoEarths
• Observing Isotopologue Bands in Terrestrial Exoplanet Atmospheres with the James Webb Space Telescope---Implications for Identifying Past Atmospheric and Ocean Loss
• Effects of UV stellar spectral uncertainty on the chemistry of terrestrial atmospheres
• Ozone chemistry on tidally locked M dwarf planets
• Is ozone a reliable proxy for molecular oxygen? I. The O2-O3 relationship for Earth-like atmospheres
• Lightning climatology of exoplanets and brown dwarfs guided by Solar System data
• Implications of different stellar spectra for the climate of tidally-locked Earth-like exoplanets
• Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets
• The Effect of Land Albedo on the Climate of Land-Dominated Planets in the TRAPPIST-1 System
• The Equatorial Jet Speed on Tidally Locked Planets: I -- Terrestrial Planets
• How does Background Air Pressure Influence the Inner Edge of the Habitable Zone for Tidally Locked Planets in a 3D View?

Cited by in corpus (5)

• 3D modelling of the impact of stellar activity on tidally locked terrestrial exoplanets: atmospheric composition and habitability
• Sporadic Spin-Orbit Variations in Compact Multi-planet Systems and their Influence on Exoplanet Climate
• Impacts of Atmospheric Carbon Species and Stellar Type on Climates of Terrestrial Planets
• The effect of a biosphere on the habitable timespan of stagnant-lid planets and implications for the atmospheric spectrum
• Hydrocarbon complexity and photochemical shielding of prebiotic feedstock molecules in exoplanet atmospheres