Abstract
The low density interstellar medium (ISM) close to the Sun and inside of the heliosphere provides a unique laboratory for studying interstellar dust grains. Grain characteristics in the nearby ISM are obtained from observations of interstellar gas and dust inside of the heliosphere and the interstellar gas towards nearby stars. Comparison between the gas composition and solar abundances suggests that grains are dominated by olivines and possibly some form of iron oxide. Measurements of the interstellar Ne/O ratio by the Interstellar Boundary Explorer spacecraft indicate that a high fraction of interstellar oxygen in the ISM must be depleted onto dust grains. Local interstellar abundances are consistent with grain destruction in ~150 km s−1 interstellar shocks, provided that the carbonaceous component is hydrogenated amorphous carbon and carbon abundances are correct. Variations in relative abundances of refractories in gas suggest variations in the history of grain destruction in nearby ISM. The large observed grains, > 1 μm, may indicate a nearby reservoir of denser ISM. Theoretical three-dimensional models of the interaction between interstellar dust grains and the solar wind predict that plumes of ~0.18 μm dust grains form around the heliosphere.
Highlights
The local interstellar medium (ISM) surrounding the Sun and inside of the heliosphere offers a unique set of diagnostics for interstellar dust grains, in a well-defined region of space
Summary Local interstellar dust shows the characteristics of dust in low density clouds, with high gas phase abundances of refractory elements that have been processed by ∼150 km s−1 shocks
Observations of interstellar oxygen both inside and outside of the heliosphere suggest high depletions that indicate an additional carrier of the oxygen such as either organic refractory particles or oxides
Summary
The local interstellar medium (ISM) surrounding the Sun and inside of the heliosphere offers a unique set of diagnostics for interstellar dust grains, in a well-defined region of space. Local clouds are partially ionized and have low column densities which lead to the need to include ionization corrections to calculate the gas phase abundances of refractory elements and thereby infer the composition of the dust (Frisch et al, 2011). In the absence of infrared-bright dense clouds, the composition of local dust is inferred from measurements of interstellar gas towards nearby stars and inside of the heliosphere.
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