Solar and heliospheric processes from solar wind composition measurements

Composition measurements in the solar wind provide important information for solar system science and astrophysics. We show in this report how ion composition data are used to investigate chromospheric and coronal processes. Isotopic abundances in the Sun can best be derived from solar wind measurements. 3 He / 4 He is an isotopic ratio with far-reaching implications. It allows us to determine the deuterium abundance in the proto-solar nebula, which in turn leads to an estimate of deuterium production in the early universe. The interstellar gas is the second most important source of heliospheric ions. Atomic abundances in the local interstellar gas are derived from ion composition measurements, and processes in the solar wind termination region and beyond are studied.

Deuterium in the Galaxy

There have been a number of attempts made in the last decade or two to observe deuterium in parts of the universe other than here in Earth. It is of interest merely to detect deuterium elsewhere just as it is to detect the occurrence of any nuclide. However in the case of deuterium there is a special interest because in big-bang cosmologies the great majority of deuterium in the universe is considered to have been formed in the initial fireball (Wagoner, 1973). Any observation of the present abundance of deuterium thus might give information about the very early stages of the creation of the universe. Detailed studies of nucleosynthesis during the early expansion of hot big-bang universes have however indicated a particular feature of deuterium production. (Fig. 1) The mass fraction produced X(D) is a very sensitive function of the size of the universe, as measured say by the present baryon density ϱb. Other nuclides that are mainly produced in the early expansion, such as 4He, have mass fractions less dependent on ϱb. Thus if we adopt the big-bang model for our universe we can determine ϱb from observations of X(D). Apart from any intrinsic interest in the present density of the’universe, there is considerable interest in whether the value is great enough for the present expansion to halt and go over to a collapse — or so small that the expansion of the universe will go on forever.