Deuterium and Helium-3 in the Protosolar Cloud

Abstract

New measurements of the isotopic composition of helium in the solar wind obtained from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses are presented and compared with earlier SWICS results and previous mass spectrometric determinations of this ratio with the Apollo Solar Wind Composition (SWC) experiment and the Ion Composition Instrument (ICI) on the International Sun Earth Explorer 3 (ISEE 3). The new SWICS data from both the fast and slow solar wind are extrapolated to the photosphere to obtain a representative value of the present-day ratio of3He/4He = (3.75 ± 0.27) × 10−4in the Outer Convective Zone (OCZ) of the Sun. After corrections of this ratio for secular changes caused by diffusion, mixing and3He production by incomplete H-burning (Vauclair 1998), we obtain (D +3He)/H = (3.6 ± 0.38) × 10−5for the Protosolar Cloud (PSC). Adopting the Jovian3He/4He ratio = (1.66 ±0.05) × 10−4measured by the Galileo Probe mass spectrometer (Mahaffy et al. 1998) as representative for the PSC, we obtain (D/H)protosolar= (1.94 ±0.39) × 10−5. Using results of galactic evolution studies (Tosi 1998, 2000) and the D and3He abundances in the Protosolar Cloud and the Local Interstellar Cloud (Linsky 1998; Gloeckler &Geiss 1998), we estimate (D/H)primordial= (2.4 − 4.2) × 10−5. This range corresponds to a universal baryon/photon ratio of (5.9−4.2) × 10−10.