Terrestrial atmospheric effects induced by counterstreaming dense interstellar cloud material

Abstract

The Solar System during its life has travelled more than 10 times through dense interstellar clouds with particle concentrations of 10 2 -10 3 cm -3 and more, compressing the heliosphere to heliopause dimensions smaller than 1 AU and thus bringing the Earth in immediate contact with the interstellar matter. For cloud concentrations greater than of 10 2 cm -3 , the flowing interstellar material even at the Earth's orbit remains completely shielded from solar wind protons and would only be subject to solar photoionization processes. We have developed a 2D-two-fluid gas-dynamical numerical code to describe the hydrodynamical behavior of the incoming interstellar gas near the Earth, taking into account both the photoionization and the gravity of the Sun. As we show, the resulting strongly increased neutral hydrogen fluxes ranging from 10 9 to 10 11 cm -2 s -1 cause substantial changes in the terrestrial atmosphere. During the phase of the immersion into the cloud the resulting flux of neutral hydrogen incident on the terrestrial atmosphere in the steady state would be balanced by the upward escape flux of H-atoms and the downward flux of water molecules, which is the product of the atmospheric hydrogen-oxygen chemistry via even-odd reaction schemes. In that case hydrogen acts as a chemical agent to remove oxygen atoms and to cause ozone concentration reductions above 50 km by a factor of 1.5 at the stratopause to about a factor of 1000 and more at the mesopause. Thus, depending on the specific encounter parameters the high mixing ratio of hydrogen in the Earth's atmosphere may substantially decrease the ozone concentration in the mesosphere and may trigger an ice age of relatively long duration.