(Ap.J., in press, 1999) by Zank and Frisch
The interplanetary environment is a sensitive indicator of the galactic environment of the Sun. The outer planets are more frequently immersed in unperturbed interstellar material than are the inner planets. The interaction of the heliosphere with a somewhat denser cloud than the one we are presently immersed in is modeled. If the density of the cloud surrounding the solar system is increased to 10 cm^-3, then the dimensions of the heliosphere shrink by an order of magnitude, and the heliopause and heliosheath regions become unstable. In addition, the flux of neutral hydrogen at the position of the Earth increases to about 2 cm^-3. Presently, all hydrogen is ionized outside of the position of the Earth. astro-ph paper number 9901279.
