Cool Stars 14 - Submitted Abstract # 355
This version created on 05 October 2006

Stellar radiation and particle induced ion-escape from CO2-rich
Earth-size and mass exoplanets within the habitable zones of dwarf
stars


Naoki Terada, National Institute of Information and Communications Technology,Nukui-Kitamachi, Koganei, Tokyo, and CREST, Japan Science and Technology Agency, Saitama, Japan
Yuri Kulikov, N.,Polar Geophysical Institute (PGI), Russian Academy of Sciences, Khalturina Str. 15, Murmansk, 183010, Russian Federation
Helmut Lammer, Space Research Institute,  Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria
Maxim Khodachenko, L., Space Research Institute,  Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria
Herbert Lichtenegger, I. M., Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria

For modelling CO2 rich thermospheres within the habitable zones (HZ)
of active dwarf stars over their history we apply a
diffusive-gravitational equilibrium and thermal balance model and
investigate the heating of the thermosphere by photodissociation and
ionization processes, due to exothermic chemical reactions and cooling
by CO2 IR emission in the 15 um band.  Our model simulations result in
expanded thermospheres.  Moreover, our results yield high exospheric
temperatures of several thousand Kelvin during the active phase of the
dwarf stars even if we assume a "dry" CO2 atmosphere with similar
composition that is observed on present Venus.  For studying how much
of the ionized part of the upper atmosphere could have been lost to
space due to a stronger solar wind and higher X-ray and EUV fluxes we
used our modelled atmospheric density profiles and studied the loss of
ions from the upper atmosphere over the planet's history by applying a
3-D magnetohydrodynamic (MHD) model as well as a numerical test
particle model.  Depending on the used stellar wind plasma parameters,
which are related to the orbital distance of the HZ our model
simulations show that ion loss could remove tens or even tens of bar
or even more of an atmosphere over a planet's lifetime.  

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