Dust cloud lightning in extraterrestrial atmospheres

Helling, Christiane; Jardine, M.; Diver, D. A.; Witte, Sören

doi:10.1016/j.pss.2012.07.003

Cited by 14 publications

(9 citation statements)

References 35 publications

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“…Cosmic rays play important effects on the chemistry and ionisation of planetary atmospheres (Helling et al 2013;Rimmer & Helling 2013). They could also be a source of genetic mutations in organisms (Atri & Melott 2012).…”

Section: Galatic Cosmic Raysmentioning

confidence: 99%

M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

Vidotto¹,

Jardine²,

Morin³

et al. 2013

Monthly Notices of the Royal Astronomical Society

171

157

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We perform three-dimensional numerical simulations of stellar winds of early-M dwarf stars. Our simulations incorporate observationally reconstructed large-scale surface magnetic maps, suggesting that the complexity of the magnetic field can play an important role in the angular momentum evolution of the star, possibly explaining the large distribution of periods in field dM stars, as reported in recent works. In spite of the diversity of the magnetic field topologies among the stars in our sample, we find that stellar wind flowing near the (rotational) equatorial plane carries most of the stellar angular momentum, but there is no preferred colatitude contributing to mass loss, as the mass flux is maximum at different colatitudes for different stars. We find that more non-axisymmetric magnetic fields result in more asymmetric mass fluxes and wind total pressures p tot (defined as the sum of thermal, magnetic and ram pressures). Because planetary magnetospheric sizes are set by pressure equilibrium between the planet's magnetic field and p tot , variations of up to a factor of 3 in p tot (as found in the case of a planet orbiting at several stellar radii away from the star) lead to variations in magnetospheric radii of about 20 percent along the planetary orbital path. In analogy to the flux of cosmic rays that impact the Earth, which is inversely modulated with the non-axisymmetric component of the total open solar magnetic flux, we conclude that planets orbiting M dwarf stars like DT Vir, DS Leo and GJ 182, which have significant non-axisymmetric field components, should be the more efficiently shielded from galactic cosmic rays, even if the planets lack a protective thick atmosphere/large magnetosphere of their own.

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Section: Galatic Cosmic Raysmentioning

confidence: 99%

M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

Vidotto¹,

Jardine²,

Morin³

et al. 2013

Monthly Notices of the Royal Astronomical Society

171

157

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“…We note that Helling and Woitke (2006) have also presented detailed models for the formation and evolution of clouds in drown dwarf atmospheres. These were subsequently applied to the atmospheric conditions of EGPs in order to investigate the composition and optical properties of clouds in these environments in relation to available observations (Lee et al 2015), the impact of the clouds on the atmospheric structure (Lee et al 2017), and the possible occurrence of lightning in these cloud structures (Helling et al 2013). Instead of the physics of cloud formation, in the current study we focus on the properties of the photochemical aerosols that can form in the upper atmosphere of EGPs.…”

Section: Introductionmentioning

confidence: 99%

Aerosol Properties of the Atmospheres of Extrasolar Giant Planets

Lavvas

Koskinen

2017

ApJ

186

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We use a model of aerosol microphysics to investigate the impact of high-altitude photochemical aerosols on the transmission spectra and atmospheric properties of close-in exoplanets, such as HD 209458 b and HD 189733 b. The results depend strongly on the temperature profiles in the middle and upper atmospheres, which are poorly understood. Nevertheless, our model of HD 189733 b, based on the most recently inferred temperature profiles, produces an aerosol distribution that matches the observed transmission spectrum. We argue that the hotter temperature of HD 209458 b inhibits the production of high-altitude aerosols and leads to the appearance of a clearer atmosphere than on HD 189733 b. The aerosol distribution also depends on the particle composition, photochemical production, and atmospheric mixing. Due to degeneracies among these inputs, current data cannot constrain the aerosol properties in detail. Instead, our work highlights the role of different factors in controlling the aerosol distribution that will prove useful in understanding different observations, including those from future missions. For the atmospheric mixing efficiency suggested by general circulation models, we find that the aerosol particles are small (∼nm) and probably spherical. We further conclude that a composition based on complex hydrocarbons (soots) is the most likely candidate to survive the high temperatures in hot-Jupiter atmospheres. Such particles would have a significant impact on the energy balance of HD 189733 b's atmosphere and should be incorporated in future studies of atmospheric structure. We also evaluate the contribution of external sources to photochemical aerosol formation and find that their spectral signature is not consistent with observations.

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“…Rimmer & Helling (2013) demonstrate that cosmic ray irradiation significantly enhances the electron fraction compared to thermal ionisation in the upper atmospheres of brown dwarfs, but the local degree of ionisation does not exceed 10 −7 in these low-density regions. Helling et al (2013) and Rimmer & Helling (2013) do further point out that CRs can affect the upper portion of the mineral clouds that form in brown dwarf atmospheres (Helling & Casewell 2014), an effect that is well established for solar system objects (Helling et al 2016a). The present paper takes the idea of environmental effects on the ionisation of atmospheres of very low-mass, ultra-cool objects one step further.…”

Section: Introductionmentioning

confidence: 93%

Environmental effects on the ionisation of brown dwarf atmospheres

Rodriguez-Barrera

Helling

Wood

2018

A&A

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Context. Brown dwarfs emit bursts of Hα, white light flares, and show radio flares and quiescent radio emission. They are suggested to form Aurorae, similar to planets in the solar system but much more energetic. All these processes require a source gas with an appropriate degree of ionisation which, so far, is mostly postulated to be sufficient. Aims. We aim to demonstrate that the galactic environment influences atmospheric ionisation, and that it hence amplifies or enables the magnetic coupling of the atmospheres of ultra-cool objects, like brown dwarfs and free-floating planets. Methods. We build on our previous work on thermal ionisation of ultra-cool atmospheres and explore the effect of environmental high-energy radiation on the atmosphere's degree of ionisation. We consider the effect of photoionisation by Lyman continuum radiation in three different environments: the InterStellar Radiation Field (ISRF), O and B stars in star forming regions, and also for white dwarf companions in binary systems. We apply our Monte Carlo radiation transfer code to investigate the effect of Lyman continuum photoionisation for prescribed atmosphere structures for very low-mass objects. Results. The external radiation environment plays an important role for the atmospheric ionisation of very low-mass, ultra-cool objects. Lyman continuum irradiation greatly increases the level of ionisation in the uppermost atmospheric regions. Our results suggest that a shell of an almost fully ionised atmospheric gas emerges for brown dwarfs in star forming regions and brown dwarfs in white dwarf binary systems. As a consequence, brown dwarf atmospheres can be magnetically coupled which is the presumption for chromospheric heating to occur and for Aurorae to emerge. First tests for assumed chromosphere-like temperature values suggest that the resulting free-free X-ray luminosities are comparable with those observed from non-accreting brown dwarfs in star forming regions.

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Dust cloud lightning in extraterrestrial atmospheres

Cited by 14 publications

References 35 publications

M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

Aerosol Properties of the Atmospheres of Extrasolar Giant Planets

Environmental effects on the ionisation of brown dwarf atmospheres

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