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| Titel |
How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability |
| VerfasserIn |
Christof Weber, Helmut Lammer, Ildar F. Shaikhislamov, Nikolai Erkaev, Joshua M. Chadney, Maxim L. Khodachenko, Jean-Mathias Grießmeier, Helmut O. Rucker, Christian Vocks, Wolfgang Macher, Petra Odert, Kristina G. Kislyakova |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141537
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| Publikation (Nr.) |
 EGU/EGU2017-5061.pdf |
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| Zusammenfassung |
| We present a study of the plasma conditions in the atmospheres of the Hot Jupiters HD
209458b and HD 189733b and for an HD 209458b-like planet at orbit locations between
0.2–1 AU around a Sun-like star. We discuss how these conditions influence the radio
emission we expect from their planetary magnetospheres. We find that the environmental
conditions for the cyclotron maser instability (CMI), the process which is responsible
for the generation of radio waves at magnetic planets in the solar system, most
likely will not operate at Hot Jupiters. The reason for that is that hydrodynamically
expanding atmospheres possess extended ionospheres whose plasma densities within the
magnetosphere are so large that the plasma frequency is much higher than the cyclotron
frequency, which contradicts the necessary condition for the production of radio
emission and prevents the escape of radio waves from close-in extrasolar planets at
distances <0.05 AU from a Sun-like host star. The upper atmosphere structure of Hot
Jupiters around stars similar to the Sun changes between 0.2 and 0.5 AU from the
hydrodynamic to a hydrostatic regime and this results in conditions similar to solar system
planets with a region of depleted plasma between the exobase and the magnetopause
where the plasma frequency can be lower than the cyclotron frequency. In such an
environment a beam of highly energetic electrons accelerated along the field lines towards
the planet can produce radio emission. However, even if the CMI could operate
the extended ionospheres of Hot Jupiters are too dense to let the radio emission
escape from the planets. 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. 0.1 and 0.2 AU. In particular we check if the atmosphere of Tau Bootis
b at 0.046 AU is in the hydrostatic or in the hydrodynamic regime. If it is in the
hydrodynamic regime it’s ionosphere is extended and will constitute an obstacle for
possibly generated radio waves or the generation via the Cyclotron Maser Instability
(CMI) might even be prevented completely. Furthermore we investigate at which
orbital location the atmosphere undergoes the transformation from hydrodynamic
to hydrostatic, i.e. the transformation to more favourable conditions for the CMI. |
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