CHARACTERISTICS OF NEARBY INTERSTELLAR MATTER

There is a warm tenuous partially ionized cloud (T similar to 10(4) K, n(HI)similar to 0.1 cm(-3)), n(HII similar to 0.22-0.44 cm(-3)) surro unding the solar system which regulates the environment of the solar s ystem, determines the structure of the heliopause region, and feeds ne utral interstellar gas into the inner solar system. The velocity (V si milar to -20 km s(-1) from l similar to 335 degrees, b similar to 0 de grees in the local standard of rest) and enhanced Ca Il and Fe II abun dances of this cloud suggest an origin as evaporated gas from cloud su rfaces in the Scorpius-Centaurus Association. Although the soft X-ray emission attributed to the 'Local Bubble' is enigmatic, optical and ul traviolet data are consistent with bubble formation caused by star for mation epochs in the Scorpius-Centaurus Association as regulated by th e nearby spiral arm configuration. The cloud surrounding the solar sys tem (the 'local fluff') appears to be the leading region of an expandi ng interstellar structure (the 'squall line') which contains a magneti c field causing polarization of the light of nearby stars, and also ab sorption features in nearby upwind stars. The velocity vectors of the solar system and local fluff are perpendicular in the local standard o f rest. Combining this information with the low column densities seen towards Sirius in the anti-apex direction, and the assumption that the cloud velocity vector is parallel to the surface normal, suggests tha t the Sun entered the local fluff within the historical past (less tha n 10000 years ago) and is skimming the surface of the cloud. Compariso n of magnesium absorption lines towards Sirius and anomalous cosmic-ra y data suggest the local fluff is in ionization equilibrium.