Constraining the Heliosphere: The Need for High-Resolution Observations   of Nearby Interstellar Matter
  High-resolution ultraviolet observations of nearby bright and faint stars are required to evaluate changes in the past and future galactic environments of the Sun, and the possibly impact of these changes on the interplanetary environment at 1 AU (around the Earth). The boundary conditions of the heliosphere and interplanetary environments are constrained by the characteristics of the surrounding interstellar material (ISM), which changes on timescales of 10^3-10^5 years. An increase in the density of the interstellar cloud surrounding the solar system to 10 cm^-3 decreases the heliosphere radius by about an order of magnitude. UV observations of nearby stars at high spectral resolution (>300,000) and high signal-to-noise are required to evaluate future modifications to heliosphere properties by the ISM. 
P. C. Frisch