Properties of the interstellar gas inside the heliosphere

Methods and results of investigations of the interstellar gas inside the heliosphere are summarized and discussed. Flow parameters of H and He and the relative abundances of H, He, N, O, and Ne in the distant heliosphere are given. Charge-exchange processes in front of the heliosphere affect the flow of hydrogen and oxygen through the heliopause. The speed of hydrogen is reduced by about 6 km/s, and screening leads to a reduction of the O/He and H/He ratios in the neutral gas entering the heliosphere. When the screening effect and the acceleration processes leading to the anomalous cosmic rays (ACR) are sufficiently understood, abundances in the local interstellar cloud (LIC) can be derived from measurements inside the heliosphere. Since isotopic ratios are virtually not changed by screening or by EUV and solar wind ionization, relative abundances of isotopes in the gaseous phase of the LIC can be determined with no or minor correction from investigations of the neutral gas, pickup ions, and ACR particles. (Author)