Lightning climatology of exoplanets and brown dwarfs guided by Solar system data

Hodosán, Gabriella; Helling, Christiane; Asensio-Torres, Rubén; Vorgul, I.; Rimmer, Paul B.

doi:10.1093/mnras/stw1571

Cited by 60 publications

(47 citation statements)

References 175 publications

(314 reference statements)

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“…The varying amount of water on the surface is predicted to have a considerable effect on the rate of lightning. We expect dry, rocky planets to have lightning flash densities equal to 17.0 − 28.9 flashes km −2 yr −1 , whereas Earth-sized planets containing water on their surface would show smaller frequency of only 0.3 − 0.6 flashes km −2 yr −1 (Hodosán et al 2016b).…”

Section: Introductionmentioning

confidence: 91%

Lightning chemistry on Earth-like exoplanets

Ardaševa

Rimmer

Waldmann

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a model for lightning shock induced chemistry that can be applied to atmospheres of arbitrary H/C/N/O chemistry, hence for extrasolar planets and brown dwarfs. The model couples hydrodynamics and the STAND2015 kinetic gas-phase chemistry. For an exoplanet analogue to the contemporary Earth, our model predicts NO and NO 2 yields in agreement with observation. We predict height-dependent mixing ratios during a storm soon after a lightning shock of NO ≈ 10 −3 at 40 km and NO 2 ≈ 10 −4 below 40 km, with O 3 reduced to trace quantities ( 10 −10 ). For an Earth-like exoplanet with a CO 2 /N 2 dominated atmosphere and with an extremely intense lightning storm over its entire surface, we predict significant changes in the amount of NO, NO 2 , O 3 , H 2 O, H 2 , and predict significant abundance of C 2 N. We find that, for the Early Earth, O 2 is formed in large quantities by lightning but is rapidly processed by the photochemistry, consistent with previous work on lightning. The effect of persistent global lightning storms are predicted to be significant, primarily due to NO 2 , with the largest spectral features present at ∼ 3.4 µm and ∼ 6.2 µm. The features within the transmission spectrum are on the order of 1 ppm and therefore are not likely detectable with JWST. Depending on its spectral properties, C 2 N could be a key tracer for lightning on Earth-like exoplanets with a N 2 /CO 2 bulk atmosphere, unless destroyed by yet unknown chemical reactions.

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Section: Introductionmentioning

confidence: 91%

Lightning chemistry on Earth-like exoplanets

Ardaševa

Rimmer

Waldmann

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…HAT-P-11b (from this work and Hodosán et al, [2016a]) and examples from across the solar system. All values are from Hodosán et al, [2016b], apart from (*), which was obtained from Huffines and Orville [1999] 2009 Mar 29 (phase 1) Table 1 lists our result for HAT-P-11b in comparison to a few examples of flash densities observed in the solar system. We only list the best case (ρ fl,1 = 114 flashes km −2 h −1 ), the example case (ρ fl,2 = 3.8 × 10 5 flashes km −2 h −1 ), and the most realistic case (ρ fl,3 = 570 flashes km −2 h −1 ) for HAT-P-11b.…”

Section: Resultsmentioning

confidence: 99%

“…Redoubt eruption showed in 2009 March 23, and thunderstorms never seen in the solar system before. However, we have to remind ourselves, that the Jovian and Saturnian values are based on data from spacecraft, which can only observe the most energetic flashes from the planet [Hodosán et al, 2016b]. Secondly, we assumed that lightning on HAT-P-11b produces the same amount of energy and radio power that is known from the solar system.…”

Section: Resultsmentioning

confidence: 99%

Exo-lightning radio emission: The case study of HAT-P-11b

2018

Planetary Radio Emissions Viii

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Lightning induced radio emission has been observed on solar system planets. Lecavelier des Etangs et al. [2013] carried out radio transit observations of the exoplanet HAT-P-11b, and suggested a tentative detection of a radio signal. Here, we explore the possibility of the radio emission having been produced by lightning activity on the exoplanet, following and expanding the work of Hodosán et al. [2016a]. After a summary of our previous work [Hodosán et al. 2016a], we extend it with a parameter study. The lightning activity of a hypothetical storm is largely dependent on the radio spectral roll-off, n, and the flash duration, τ fl. The best-case scenario would require a flash density of the same order of magnitude as can be found during volcanic eruptions on Earth. On average, 3.8 × 10 6 times larger flash densities than Earth-storms with the largest lightning activity are needed to produce the observed signal from HAT-P-11b. Combined with the results of Hodosán et al. [2016a] regarding the chemical effects of planet-wide thunderstorms, we conclude that future radio and infrared observations may lead to lightning detection on planets outside the solar system.

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“…Within cloud regions (p gas ≈ 10 −5 −1 bar), lightning also contributes to the overall ionisation fraction of the atmosphere yielding degrees of ionisation of about 10 −1 (Guo et al 2009;Beyer & Shevelko 2003), where a single discharge event can have characteristic vertical length scales ≈ 0.5 − 4 km, affecting atmospheric volumes of the order of 10 4 − 10 10 m 3 (Bailey et al 2014). For multiple discharge events, the atmospheric volume affected can be significantly enhanced; for example, Hodosán et al (2016) estimate the total number of lightning flashes of exoplanets to be of the order of 10 5 − 10 12 during a transit. Alfvén ionisation (AI) occurs when a neutral gas collides with a low-density magnetised seed plasma and their relative motion reaches a critical threshold speed.…”

Section: Introductionmentioning

confidence: 99%

Dust cloud evolution in sub-stellar atmospheres via plasma deposition and plasma sputtering

Stark¹,

Diver

2018

A&A

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Context. In contemporary sub-stellar model atmospheres, dust growth occurs through neutral gas-phase surface chemistry. Recently, there has been a growing body of theoretical and observational evidence suggesting that ionisation processes can also occur. As a result, atmospheres are populated by regions composed of plasma, gas and dust, and the consequent influence of plasma processes on dust evolution is enhanced. Aims. This paper aims to introduce a new model of dust growth and destruction in sub-stellar atmospheres via plasma deposition and plasma sputtering. Methods. Using example sub-stellar atmospheres from Drift-Phoenix, we have compared plasma deposition and sputtering timescales to those from neutral gas-phase surface chemistry to ascertain their regimes of influence. We calculated the plasma sputtering yield and discuss the circumstances where plasma sputtering dominates over deposition. Results. Within the highest dust density cloud regions, plasma deposition and sputtering dominates over neutral gas-phase surface chemistry if the degree of ionisation is 10 −4 . Loosely bound grains with surface binding energies of the order of 0.1 − 1 eV are susceptible to destruction through plasma sputtering for feasible degrees of ionisation and electron temperatures; whereas, strong crystalline grains with binding energies of the order 10 eV are resistant to sputtering. Conclusions. The mathematical framework outlined sets the foundation for the inclusion of plasma deposition and plasma sputtering in global dust cloud formation models of sub-stellar atmospheres.

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Lightning climatology of exoplanets and brown dwarfs guided by Solar system data

Cited by 60 publications

References 175 publications

Lightning chemistry on Earth-like exoplanets

Lightning chemistry on Earth-like exoplanets

Exo-lightning radio emission: The case study of HAT-P-11b

Dust cloud evolution in sub-stellar atmospheres via plasma deposition and plasma sputtering

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