IONIZATION OF EXTRASOLAR GIANT PLANET ATMOSPHERES

Journal Article · Sun Oct 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/178· OSTI ID:21464723

Koskinen, Tommi T ^[1]; Cho, James Y-K ^[2]; Achilleos, Nicholas

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1. Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ (United States)
2. Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS (United Kingdom)

Many extrasolar planets orbit close in and are subject to intense ionizing radiation from their host stars. Therefore, we expect them to have strong, and extended, ionospheres. Ionospheres are important because they modulate escape in the upper atmosphere and can modify circulation, as well as leave their signatures, in the lower atmosphere. In this paper, we evaluate the vertical location Z{sub I} and extent D{sub I} of the EUV ionization peak layer. We find that Z{sub I{approx}}1-10 nbar-for a wide range of orbital distances (a = 0.047-1 AU) from the host star-and D{sub I}/H{sub p{approx}}>15, where H{sub p} is the pressure scale height. At Z{sub I}, the plasma frequency is {approx}80-450 MHz, depending on a. We also study global ion transport, and its dependence on a, using a three-dimensional thermosphere-ionosphere model. On tidally synchronized planets with weak intrinsic magnetic fields, our model shows only a small, but discernible, difference in electron density from the dayside to the nightside ({approx}9 x 10{sup 13} m{sup -3} to {approx}2 x 10{sup 12} m{sup -3}, respectively) at Z{sub I}. On asynchronous planets, the distribution is essentially uniform. These results have consequences for hydrodynamic modeling of the atmospheres of close-in extrasolar giant planets.

• OSTI ID: 21464723
• Journal Information: Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/178; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ELECTRON DENSITY
IONIZATION
IONIZING RADIATIONS
IONOSPHERE
LANGMUIR FREQUENCY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
PLANETARY ATMOSPHERES
PLANETS
SIMULATION
STAR EVOLUTION
STARS
THERMOSPHERE
ATMOSPHERES
EARTH ATMOSPHERE
EVOLUTION
FLUID MECHANICS
HYDRODYNAMICS
MECHANICS
RADIATIONS