Escape and evolution of Titan's N${}_2$ atmosphere constrained by ${}^{14}$N/${}^{15}$N isotope ratios

Abstract

We apply a 1D upper atmosphere model to study thermal escape of nitrogen over Titan's history. Significant thermal escape should have occurred very early for solar EUV fluxes 100 to 400 times higher than today with escape rates as high as $\approx 1.5\times 10^{28}$ s${}^{-1}$ and $\approx 4.5\times 10^{29}$ s${}^{-1}$, respectively, while today it is $\approx 7.5\times 10^{17}$ s${}^{-1}$. Depending on whether the Sun originated as a slow, moderate or fast rotator, thermal escape was the dominant escape process for the first 100 to 1000 Myr after the formation of the solar system. If Titan's atmosphere originated that early, it could have lost between $\approx 0.5-16$ times its present atmospheric mass depending on the Sun's rotational evolution. We also investigated the mass-balance parameter space for an outgassing of Titan's nitrogen through decomposition of NH${}_3$-ices in its deep interior. Our study indicates that, if Titan's atmosphere originated at the beginning, it could have only survived until today if the Sun was a slow rotator. In other cases, the escape would have been too strong for the degassed nitrogen to survive until present-day, implying later outgassing or an additional nitrogen source. An endogenic origin of Titan's nitrogen partially through NH${}_3$-ices is consistent with its initial fractionation of ${}^{14}$N/${}^{15}$N $\approx$ 166 - 172, or lower if photochemical removal was relevant for longer than the last $\approx$ 1,000 Myr. Since this ratio is slightly above the ratio of cometary ammonia, some of Titan's nitrogen might have originated from refractory organics.

arXiv comment16 pages, 6 figures. This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS) following peer review. The version of record [https://doi.org/10.1093/mnras/staa3151] is available online at: https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/staa3151/5930166

References in corpus (23)

• The origins and concentrations of water, carbon, nitrogen and noble gases on Earth
• The timeline of the Lunar bombardment - revisited
• The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• Phase Separation in Giant Planets: Inhomogeneous Evolution of Saturn
• Origin and Loss of nebula-captured hydrogen envelopes from "sub"- to "super-Earths" in the habitable zone of Sun-like stars
• The Evolution of Stellar Rotation and the hydrogen atmospheres of habitable-zone Terrestrial Planets
• A grid of upper atmosphere models for 1--40 MEARTH planets: application to CoRoT-7 b and HD219134 b,c
• Thermally-driven atmospheric escape: Transition from hydrodynamic to Jeans escape
• Submillimeter Observations of Titan: Global Measures of Stratospheric Temperature, CO, HCN, HC3N, and the Isotopic Ratios 12C/13C and 14N/15N
• Probing the Blow-Off Criteria of Hydrogen-Rich "Super-Earths"
• XUV exposed non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part I: Atmospheric expansion and thermal escape
• Stellar Winds on the Main-Sequence I: Wind Model
• Onset of giant planet migration before 4480 million years ago
• The Upper Atmospheres of Terrestrial Planets: Carbon Dioxide Cooling and the Earth's Thermospheric Evolution
• Thermal mass loss of protoplanetary cores with hydrogen-dominated atmospheres: The influences of ionization and orbital distance
• ALMA Observations of HCN and its Isotopologues on Titan
• Extreme hydrodynamic atmospheric loss near the critical thermal escape regime
• Molecular-Kinetic Simulations of Escape from the Ex-planet and Exoplanets: Criterion for Transonic Flow
• Was the Sun a Slow Rotator? -- Sodium and Potassium Constraints from the Lunar Regolith
• Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters
• Stability of Ice/Rock Mixtures with Application to a Partially Differentiated Titan
• Evolution of an Early Titan Atmosphere: Comment

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