Our Local Galactic Neighborhood

Map of the local galactic neighborhood showing the Sun located near the edge of our local interstellar cloud (LIC). The star Alpha-Centauri is located just over 4 light-years away in the neighboring G-cloud complex. Outside these clouds, the density may be lower than 0.001 atoms/cc. Our Sun and the LIC have a relative velocity of 26 km/sec.

Our present knowledge of the interstellar medium surrounding our heliosphere comes either from astronomical observations that average over long lines of sight or in situ measurements of the neutral gas and larger dust grains that penetrate the heliosphere. Interstellar Probe will, for the first time, directly sample the physical properties of the interstellar medium, free from uncertainties that plague the interpretation of data acquired over astronomical lines-of-sight, and free from uncertainties arising from the exclusion of plasma, small dust particles and low-energy cosmic rays from the heliosphere.

The Sun is located near the edge of a great void in interstellar matter known as the "local bubble" that is filled with hot low-density plasma. Several thousand years ago the Sun entered our local interstellar cloud (LIC), one of several nearby clouds composed of warm, low density (~0.3 atoms/cm3) material blowing at us from the direction of the Scorpius and Centaurus constellations.

During the Sun's journey through the Galaxy it encounters a range of environments, and interstellar densities ranging from 10-5 to 105 atoms/cm3 are observed in our galactic neighborhood. Hydrodynamic simulations show that if the solar system were to enter a typical diffuse cloud with a density of 10 atoms/cm3, the size of the heliosphere would shrink by nearly a factor of ten, with significant effects on the interplanetary environment at 1 AU. By targeting Interstellar Probe to fly upstream of the Sun's motion, it will explore the future environment of the solar system over the coming decades.



Interstellar Medium
Interaction Between the Interstellar Medium and the Solar Wind
The Outer Solar System
Scientific Instruments and Mission Requirements
Table of Contents


For more information regarding this website
and the Interstellar Probe Project,
please contact Dr. Paulett Liewer

This site was last updated:
February 8, 2000.