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Ann. Geophys., 21, 1263-1273, 2003
www.ann-geophys.net/21/1263/2003/
© European Geosciences Union 2003
Consequences of the Solar System passage through dense interstellar clouds
A. G. Yeghikyan1,2 and H. J. Fahr1
1Institute of Astrophysics and Extraterrestrial Research, University of Bonn, Germany
2Byurakan Astrophysical Observatory, Armenia
Abstract. Several consequences of
the passage of the solar system through dense interstellar molecular clouds are
discussed. These clouds, dense (more than 100 cm-3), cold (10–50
K) and extended (larger than 1 pc), are characterized by a gas-to-dust mass
ratio of about 100, by a specific power grain size spectrum (grain radii
usually cover the range 0.001–3 micron) and by an average dust-to-gas number
density ratio of about 10-12. Frequently these clouds contain
small-scale (10–100 AU) condensations with gas concentrations ranging up to
10 5 cm-3. At their casual passage over the solar system they exert
pressures very much enhanced with respect to today’s standards. Under these
conditions it will occur that the Earth is exposed directly to the interstellar
flow. It is shown first that even close to the Sun, at 1 AU, the cloud’s
matter is only partly ionized and should mainly interact with the solar wind by
charge exchange processes. Dust particles of the cloud serve as a source of
neutrals, generated by the solar UV irradiation of dust grains, causing the
evaporation of icy materials. The release of neutral atoms from dust grains is
then followed by strong influences on the solar wind plasma flow. The behavior
of the neutral gas inflow parameters is investigated by a 2-D hydrodynamic
approach to model the interaction processes. Because of a reduction of the
heliospheric dimension down to 1 AU, direct influence of the cloud’s matter
to the terrestrial environment and atmosphere could be envisaged.
Key words. Interplanetary physics (heliopause
and solar wind termination; interplanetary dust; interstellar gas)
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