The galactic environment of the Sun

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun and constrains the physical characteristics of the interplanetary medium. This paper compares interstellar dust grain properties observed within the solar system with dust properties inferred from observations of the cloud surrounding the solar system. Properties of diffuse clouds in the solar vicinity are discussed to gain insight into the properties of the diffuse cloud complex flowing past the Sun. Evidence is presented for changes in the galactic environment of the Sun within the next 10$^4$--10$^6$ years. The combined history of changes in the interstellar environment of the Sun, and solar activity cycles, will be recorded in the variability of the ratio of large- to medium-sized interstellar dust grains deposited onto geologically inert surfaces. Combining data from lunar core samples in the inner and outer solar system will assist in disentangling these two effects.Comment: 30 pages, 2 figures, JGR-Space Physics, in pres

The Solar Galactic Environment

Combined heliosphere-astronomical data and models enrich our understanding both of effects the solar galactic environment might have on the inner heliosphere, and of interstellar clouds. Present data suggest that FeII/DI increases toward the upwind direction of the cluster of interstellar clouds (CLIC) flowing past the Sun. Cloud kinematics and abundances suggest an origin related to a supershell around the Scorpius-Centaurus Association. The solar space trajectory indicates the Sun entered the CLIC gas relatively recently.Comment: 3rd Annual IGPP-UCR Astrophysics Conference: Physics of the Outer Heliosphere [AIP

Boundary Conditions of the Heliosphere

Radiative transfer equilibrium models of nearby interstellar matter (ISM) yield the boundary conditions of the heliosphere when constrained with observations of ISM inside and outside of the heliosphere. Filtration factors for interstellar neutrals crossing the heliosheath region, from charge exchange with interstellar plasma, are given for H, He, N, O, Ar, and Ne. The best models predict n(HI)~0.2 /cc, n(e)~0.1 /cc, however if the isotropic 2 kHz emission observed by Voyager (Kurth & Gurnett 2003) is formed in the surrounding ISM, an alternate model with lower electron densities is indicated. Observations of nearby ISM, the radiative transfer models, and historical 10Be records provide information on past variations in the galactic environment of the Sun

Local Interstellar Matter: The Apex Cloud

Several nearby individual low column density interstellar cloudlets have been identified based on kinematical features evident in high-resolution CaII observations near the Sun. One of these cloudlets, the ``Aquila-Ophiuchus'' cloud, is within 5 pc of the Sun and located in the solar apex direction. The velocity vector of this Apex Cloud is reevaluated and components at this velocity are found towards 17 stars with distances 1--60 pc, and located primarily in the galactic center hemisphere. The Apex Cloud is the most likely candidate for the ``next'' interstellar cloud to be encountered by the Sun