For an article on the Local Fluff she calls the Local Interstellar cloud, or just our local cloud, the whispy, benign cloud now in contact with and entering the Solar System see http://www.americanscientist.org/issues/feature/2000/1/the-galactic-environment-of-the-sun/1 .  Note that it is benign because of its characteristics. Its density is less than 0.001 atoms per cubic centimeter compared to the average cloud 0.3 atoms per cubic centimenter, or 300 times denser.

Dr. Priscilla Frish, its author, explains in American Scientist Magazine, January 2000, how all of this works. Dr. Frish is Senior Scientist, Department of Astronomy and Astrophysics at the University of Chicago. Note the article was written before Voyager discovered the vast cloud that The Infinity Option story involves us with. Nevertheless the article is informative about the mechanics by which cloud matter penetrates into the Solar System.

She says, “We do not know whether the interstellar cloud complex flowing past the sun is a homogeneous structure.” Discussing the possibility of encountering more typical formations among the cloud, she continues, “My colleague Gary Zank at the Univerity of Delaware and I have recently modeled the changes that might take place should the heliosphere encounter a dense interstellar cloud. If the density of the Local Interstellar Cloud increased to 10 particles per cubic centimeter, the heliopsphere would contract to a radius of about 15 AU and the heliopause would become unstable (oscillating in and out of existence)…[It] would dramatically alter the interplanetary environment of the earth. (By comparison, virtually all of the interstellar hydrogen is ionized before it gets to the earth’s orbit under current conditions.) A more severe scenario–say a cloud with a density of 1,000 atoms pere cubic centimeter–would alter heliosphere physics entirely and probably contract the heliosphere to within a few AU of the sun. Planets such as Saturn, Uranus, Neptune and Pluto (all of which are outside 9 AU) would be fully exposed to the flux of interstellar neutrals. Interstellar gas would overwhelm the solar wind at 1 AU.” AU are Astronomical Units. One AU is the average distance between Earth and the Sun.

Dr. Frish then calls our attention to the fact of earthbound evidence of previous interstellar cosmic ray influxes thirty-three thousand and sixty thousand years ago. Ice-core samples from the Antarctic show spikes in the concentration of beryllium-10. Scientists study it based on its 1.5 million year half-life and have determined a sudden increase in cosmic-rays would be best explained by intrusions of denser parts of the Local Interstellar Cloud.

The Infinity Option story involves the threat of such a dense cloud formation and Earth intersecting within seventy years.