Knowledge about the origin and evolution of our solar system, our galaxy, and the universe can be gained by determining the composition of matter. The measured abundances of the elements and isotopic ratios help constrain cosmological models. The composition of our solar system reveals interstellar matter of the protosolar nebula some 4.5 billion years ago. A sample of the present-day galaxy with reliable observations of a number of important elemental and isotopic abundance ratios is missing. Unlike the ionized component of the interstellar gas, which is excluded from penetrating inside the heliosphere by the solar wind plasma, the neutral component of the interstellar gas can penetrate deeply into the heliosphere and therefore might be measured even as close to the Sun as the Earth's orbit. This measurement yields direct information about the composition of the local interstellar medium. Moreover, energetic neutral particles, which are produced by charge-exchange between interstellar neutral gas and heliospheric particles can be measured. A two-dimensional image of the interstellar neutral fluxes helps infer the interaction processes between the local interstellar medium and the heliosphere. We expect to detect mainly atomic particles (H, He, O) since they are much more abundant than molecules in the local interstellar gas.
An other application of neutral particle imaging is the observation of planetary magnetospheres where neutral particles are produced by charge exchange between magnetospheric particles and the planetary neutral background gas. Two-dimensional imaging of these particle fluxes allows to remotely investigate planetary magnetospheres on a global scale.
March 2001 - Martin Wieser, Physikalisches Institut, University of Berne, Switzerland