Imperial College London
Alternate

ProfessorMarinaGaland

Faculty of Natural Sciences, Department of Physics

Professor in Planetary Science
 
 
 
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Contact

 

m.galand Website

 
 
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Location

 

Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Chadney:2016:0004-6361/201527442,
author = {Chadney, JM and Galand, M and Koskinen, TT and Miller, S and Sanz-Forcada, J and Unruh, YC and Yelle, RV},
doi = {0004-6361/201527442},
journal = {Astronomy & Astrophysics},
title = {EUV-driven ionospheres and electron transport on extrasolar giant  planets orbiting active stars},
url = {http://dx.doi.org/10.1051/0004-6361/201527442},
volume = {587},
year = {2016}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - The composition and structure of the upper atmospheres of Extrasolar GiantPlanets (EGPs) are affected by the high-energy spectrum of their host starsfrom soft X-rays to EUV. This emission depends on the activity level of thestar, which is primarily determined by its age. We focus upon EGPs orbiting K-and M-dwarf stars of different ages. XUV spectra for these stars areconstructed using a coronal model. These spectra are used to drive both athermospheric model and an ionospheric model, providing densities of neutraland ion species. Ionisation is included through photo-ionisation andelectron-impact processes. We find that EGP ionospheres at all orbitaldistances considered and around all stars selected are dominated by thelong-lived H$^+$ ion. In addition, planets with upper atmospheres where H$_2$is not substantially dissociated have a layer in which H$_3^+$ is the major ionat the base of the ionosphere. For fast-rotating planets, densities ofshort-lived H$_3^+$ undergo significant diurnal variations, with the maximumvalue being driven by the stellar X-ray flux. In contrast, densities oflonger-lived H$^+$ show very little day/night variability and the magnitude isdriven by the level of stellar EUV flux. The H$_3^+$ peak in EGPs with upperatmospheres where H$_2$ is dissociated under strong stellar illumination ispushed to altitudes below the homopause, where this ion is likely to bedestroyed through reactions with heavy species. The inclusion of secondaryionisation processes produces significantly enhanced ion and electron densitiesat altitudes below the main EUV ionisation peak, as compared to models that donot include electron-impact ionisation. We estimate infrared emissions fromH$_3^+$, and while, in an H/H$_2$/He atmosphere, these are larger from planetsorbiting close to more active stars, they still appear too low to be detectedwith current observatories.
AU  - Chadney,JM
AU  - Galand,M
AU  - Koskinen,TT
AU  - Miller,S
AU  - Sanz-Forcada,J
AU  - Unruh,YC
AU  - Yelle,RV
DO  - 0004-6361/201527442
PY  - 2016///
SN  - 1432-0746
TI  - EUV-driven ionospheres and electron transport on extrasolar giant  planets orbiting active stars
T2  - Astronomy & Astrophysics
UR  - http://dx.doi.org/10.1051/0004-6361/201527442
UR  - http://hdl.handle.net/10044/1/29390
VL  - 587
ER  -
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