The interaction of the heliosphere with interstellar clouds has attracted interest since the late 1920 ’ s , both with a view to explaining apparent quasi-periodic climate “ catastrophes ” as well as periodic mass extinctions .
Until recently , however , models describing the solar wind - local interstellar medium ( LISM ) interaction self-consistently had not been developed .
Here , we describe the results of a two-dimensional ( 2D ) simulation of the interaction between the heliosphere and an interstellar cloud with the same properties as currently , except that the H ^ { o } density is increased from the present value of n ( H ^ { o } ) \sim 0.2 cm ^ { -3 } to 10 cm ^ { -3 } .
The mutual interaction of interstellar neutral hydrogen and plasma is included .
The heliospheric cavity is reduced considerably in size ( approximately 10 – 14 au to the termination shock in the upstream direction ) and is highly dynamical .
The interplanetary environment at the orbit of the Earth changes markedly , with the density of interstellar H ^ { o } increasing to \sim 2 cm ^ { -3 } .
The termination shock itself experiences periods where it disappears , reforms and disappears again .
Considerable mixing of the shocked solar wind and LISM occurs due to Rayleigh-Taylor-like instabilities at the nose , driven by ion-neutral friction .
Implications for two anomalously high concentrations of ^ { 10 } Be found in Antarctic ice cores 33 kya and 60 kya , and the absence of prior similar events , are discussed in terms of density enhancements in the surrounding interstellar cloud .
The calculation presented here supports past speculation that the galactic environment of the Sun moderates the interplanetary environment at the orbit of the Earth , and possibly also the terrestrial climate .