3D Aeronomy modelling of close-in exoplanets

Шайхисламов, И. Ф.; Khodachenko, M. L.; Lämmer, H.; Berezutsky, A. G.; Мирошниченко, И. Б.; Руменских, М. С.

doi:10.1093/mnras/sty2652

Cited by 49 publications

(54 citation statements)

References 42 publications

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“…The revealed influence of the helium abundance on the HI, OI and MgII absorption (see also Shaikhislamov et al 2018b) and the obtained constrains in that respect, may be of interest regarding the recent observations in He lines (Oklopčić et al 2018). In particular, it has been shown that the absorption in all considered lines decreases at He abundancies above 0.1 due to the decrease of atmospheric height scale and the related steeper decrease of the density with the height.…”

Section: Discussionmentioning

confidence: 68%

“…Since the cross-section of He photo-ionization at Eph >24.6 eV is an order of magnitude higher than that of the HI photo-ionization, this effect is not small. Second, even at relatively low abundancy ~3% helium significantly increases, due to its photoionization, the density of electrons in the upper atmosphere below the thermosphere maximum (Shaikhislamov et al 2018b). Therefore, the photoelectrons would lose their energy via Coulomb collisions more rapidly.…”

Section: The Numerical Model and Absorption Parametersmentioning

confidence: 99%

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3D Modeling of absorption by various species for hot jupiter HD209458b

Шайхисламов

Khodachenko

Lämmer

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The absorption of stellar radiation observed by the HD209458b in resonant lines of OI and CII has not yet been satisfactorily modeled. In our previous 2D simulations we have shown that the hydrogendominated upper atmosphere of HD209458b, heated by XUV radiation, expands supersonically beyond the Roche lobe and drags the heavier species along with it. Assuming solar abundances, OI and CII particles accelerated by tidal forces to velocities up to 50 km/s should produce the absorption due to Doppler resonance mechanism at the level of 6-10%, consistent with the observations. Since the 2D geometry does not take into account the Coriolis force in the planet reference frame, the question remained to which extent the spiraling of the escaping planetary material and its actually achieved velocity may influence the conclusions made on the basis of 2D modeling. In the present paper we apply for the first time in the study of HD209458b a global 3D hydrodynamic multi-fluid model that self-consistently describes the formation and expansion of the escaping planetary wind, affected by the tidal and Coriolis forces, as well as by the surrounding stellar wind. The modeling results confirm our previous findings that the velocity and density of the planetary flow are sufficiently high to produce the absorption in HI, OI, and CII resonant lines at the level close to the in-transit observed values. The novel finding is that the matching of the absorption measured in MgII and SiIII lines requires at least 10 times lower abundances of these elements than the Solar system values.

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Section: Discussionmentioning

confidence: 68%

Section: The Numerical Model and Absorption Parametersmentioning

confidence: 99%

3D Modeling of absorption by various species for hot jupiter HD209458b

Шайхисламов

Khodachenko

Lämmer

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…This indicates a presence of a massive hydrogen cloud around this planet, which obscures almost half of the emission in the stellar Lyα line (the absorption during a transit is ≈56%). Numerical modeling confirms that GJ 436b is surrounded by a big cloud of atomic hydrogen with a complex structure (Bourrier et al , 2016Loyd et al 2017;Shaikhislamov et al 2018).…”

Section: Model Descriptionmentioning

confidence: 90%

“…fore, atomic hydrogen is the main atmospheric component thorough most of our simulation domain for the lower atmosphere (Shaikhislamov et al 2018). Some works (Hu et al 2015) have shown that planets like GJ 436b might accumulate a significant amount of helium due to faster atmospheric escape of hydrogen.…”

Section: Model Validation Gj 436bmentioning

confidence: 98%

Transit Lyman-α signatures of terrestrial planets in the habitable zones of M dwarfs

Kislyakova

Holmström

Odert

et al. 2019

A&A

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Aims. We modeled the transit signatures in the Lyman-alpha (Lyα) line of a putative Earth-sized planet orbiting in the habitable zone (HZ) of the M dwarf GJ 436. We estimated the transit depth in the Lyα 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. For all types of atmospheres, we calculated the in-transit absorption they would produce in the stellar Lyα line. We applied it to the out-of-transit Lyα observations of GJ 436 obtained by the Hubble Space Telescope 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. Methods. We used a direct simulation Monte Carlo (DSMC) code to model the planetary exospheres. The code includes several species and traces neutral particles and ions. It includes several ionization mechanisms, such as charge exchange with the stellar wind, photo-and electron impact ionization, and allows to trace particles collisions. 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. Results. We showed that for a small rocky Earth-like planet orbiting in the HZ of GJ 436 only the hydrogen-dominated atmosphere is marginally detectable with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (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 Lyα observations of GJ 436b can be reproduced reasonably well assuming a hydrogendominated atmosphere, both in the blue and red wings of the Lyα line, which indicates that warm Neptune-like planets are a suitable target for Lyα observations. Terrestrial planets, on the other hand, can be observed in the Lyα line if they orbit very nearby stars, or if several observational visits are available.

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“…Fully hydrodynamic models of planetary upper atmospheres have so far only been applied to H and He dominated atmospheres (e.g., Khodachenko et al 2015;Owen & Mohanty 2016;Shaikhislamov et al 2018) and to an atomic H and O gas by Guo (2019). In this letter, we study for the first time the hydrodynamic outflow of an atmosphere composed of heavier molecules orbiting a very active star.…”

Section: Introductionmentioning

confidence: 99%

Extreme hydrodynamic losses of Earth-like atmospheres in the habitable zones of very active stars

Johnstone

Khodachenko

Lüftinger

et al. 2019

A&A

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Aims. In this letter, we calculate for the first time the full transonic hydrodynamic escape of an Earth-like atmosphere. We consider the case of an Earth-mass planet with an atmospheric composition identical to that of the current Earth orbiting at 1 AU around a young and very active solar mass star. Methods. To model the upper atmosphere, we used the Kompot Code, which is a first-principles model that calculates the physical structures of the upper atmospheres of planets, taking into account hydrodynamics and the main chemical and thermal processes taking place in the upper atmosphere of a planet. This model enabled us to calculate the 1D vertical structure of the atmosphere using as input the high-energy spectrum of a young and active Sun.Results. The atmosphere has the form of a transonic hydrodynamic Parker wind, which has an outflow velocity at the upper boundary of our computational domain that exceeds the escape velocity. The outflowing gas is dominated by atomic nitrogen and oxygen and their ion equivalents and has a maximum ionization fraction of 20%. The mass outflow rate is found to be 1.8 × 10 9 g s −1 , which would erode the modern Earth's atmosphere in less than 0.1 Myr. Conclusions. This extreme mass loss rate suggests that an Earth-like atmosphere cannot form when the planet is orbiting within the habitable zone of a very active star. Instead, such an atmosphere can only form after the activity of the star has decreased to a much lower level. This happened in the early atmosphere of the Earth, which was likely dominated by other gases such as CO2. Since the time it takes for the activity of a star to decay is highly dependent on its mass, this is important for understanding possible formation timescales for planets orbiting low-mass stars.

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3D Aeronomy modelling of close-in exoplanets

Cited by 49 publications

References 42 publications

3D Modeling of absorption by various species for hot jupiter HD209458b

3D Modeling of absorption by various species for hot jupiter HD209458b

Transit Lyman-α signatures of terrestrial planets in the habitable zones of M dwarfs

Extreme hydrodynamic losses of Earth-like atmospheres in the habitable zones of very active stars

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