Local interstellar cloud(s) observations with the GHRS

Thanks to its exceptional combination of resolution, sensitivity, stability, and correction refinements allowing the detection of very small amounts of absorbing gas, the GHRS has brought important information on the interstellar environment of the Sun, at a scale of the order of a parsec (or even less), through observations of very nearby stars. Some of the physical properties of the little Local Interstellar Cloud (the cloud the Sun is traveling through, or LIC), are now well established (motion, temperature, abundances), allowing a link with heliospheric gas observations. Surprisingly, the ionization degree of the LIC inferred from the magnesium-ionization state, and which controls the size of our heliosphere, seems to be larger than what radiation-field studies do predict, something not well explained. It is possible now to begin drawing a first rough picture of our solar environment. Strangely, the Sun seems to be at a boundary between two clouds, with different velocities, temperatures, and abundances. The existence of a rather weak shock having already passed the LIC and responsible for the separation into the two observed media is discussed. The observation of such nearby shocks could provide a way to estimate the local interstellar magnetic field, otherwise inaccessible.