ON THE FORM OF THE 1987 HYDROGEN SPECTRUM IN THE OUTER HELIOSPHERE

An observed bulge in the 1987 Voyager 2 hydrogen spectrum, relative to the spectrum measured in 1985, has previously been explained as due to the detection of anomalous hydrogen. It is shown in this paper that this bulging can also be naturally explained as a simple modulation phenomenon. In fact, due to energy losses, a locally accelerated, or anomalous hydrogen component is difficult to separate from the Galactic component deep inside the heliosphere. A recent investigation of Pioneer 10 observations, made much further out in the heliosphere than those of Voyager 2, did also not reveal conclusive evidence for the presence of anomalous hydrogen.