COSMIC DEUTERIUM OF A HYDROGEN INTERLOPER

Two groups have independently reported the possible detection of extra galactic deuterium in the absorption spectrum of the same high-redshif t, low-metallicity QSO. Although the high value for the inferred deute rium abundance poses no problems for cosmology (i.e. big bang nucleosy nthesis), it is in apparent conflict with Solar system observations of deuterium and helium-3. This latter inconsistency is explained and ma de quantitative, and it is shown that, unless the inferred D/H ratio i s too high by a factor of 3, these data challenge our understanding of the stellar and Galactic evolution of helium-3. This conflict is reso lved if the observed absorption feature is, in fact, due to a hydrogen interloper rather than to high-z, low-Z deuterium.