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On the Cyclotron Maser Instability in Magnetospheres of Hot Jupiters - Influence of ionosphere models

Abstract : A study of the plasma conditions in the atmosphere and ionosphere of the Hot Jupiter HD 209458b and for an HD 209458b-like planet at orbit locations of 0.2-1 AU around a Sun-like star is presented. It is discussed how these conditions influence the radio emission expected from the planet's magnetosphere. We find that the cyclotron maser instability (CMI) most likely will not operate at Hot Jupiters. It is found that close-in gas giants possess hydrodynamically expanding atmospheres and extended ionospheres with too high plasma densities within their magnetospheres, i.e. the plasma frequency is much higher than the cyclotron frequency, which is a contradiction to the necessary condition for the production of radio emission and also prevents the escape of radio waves for close-in extrasolar planets at distances <0.05 AU from a Sun-like host star. The structure of the upper atmosphere of Hot Jupiters around stars similar to the Sun changes for orbital distances between 0.2 and 0.5 AU from the hydrodynamic to a hydrostatic regime. This results in conditions where the plasma frequency can be lower than the cyclotron frequency, because a region of depleted plasma between the exobase and magnetopause can form. Like for e.g. Earth, in such an environment a beam of highly energetic electrons can propagate and be accelerated along the field lines towards the planet to produce radio emission. We also investigate the possible radio emission of the Hot Jupiter Tau Bootis b by placing it at different orbital distances from the host star, i.e. 0.046, 0.1 and 0.2 AU. It is checked if the atmosphere of Tau Bootis b at 0.046 AU is in the hydrodynamic or hydrostatic regime. In the hydrodynamic regime its ionosphere is extended and constitutes an obstacle for possibly generated radio waves; also, the generation via the Cyclotron Maser Instability (CMI) might be fully prevented.
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Submitted on : Saturday, February 12, 2022 - 6:11:50 PM
Last modification on : Tuesday, May 10, 2022 - 3:24:58 PM
Long-term archiving on: : Friday, May 13, 2022 - 6:29:41 PM

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C. Weber, H. Lammer, I. -F. Shaikhislamov, J. -M. Chadney, N. Erkaev, et al.. On the Cyclotron Maser Instability in Magnetospheres of Hot Jupiters - Influence of ionosphere models. Planetary Radio Emissions VIII, 2017, Vienne, Austria. pp.317-329, ⟨10.1553/PRE8s317⟩. ⟨insu-03568967⟩

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