Voyager 1/UVS Lyman α Measurements at the Distant Heliosphere (90-130 AU): Unknown Source of Additional Emission

In this work, we present for the first time the Lyman alpha intensities measured by Voyager 1/UVS in 2003-2014 (at 90-130 AU from the Sun). During this period Voyager 1 measured the Lyman alpha emission in the outer heliosphere at an almost fixed direction close to the upwind (i.e."toward the interstellar flow). The data show an unexpected behavior in 2003-2009: the ratio of observed intensity to the solar Lyman alpha flux is almost constant. Numerical modeling of these data is performed in the frame of a state-of-the-art self-consistent kinetic-MHD model of the heliospheric interface. The model results, for various interstellar parameters, predict a monotonic decrease of intensity not seen in the data. We propose two possible scenarios that explain the data qualitatively. The first is the formation of a dense layer of hydrogen atoms near the heliopause. Such a layer would provide an additional backscattered Doppler-shifted Lyman alpha emission, which is not absorbed inside the heliosphere and may be observed by Voyager. About 35 R of intensity from the layer is needed. The second scenario is an external nonheliospheric Lyman alpha component, which could be galactic or extragalactic. Our parametric study shows that similar to 25 R of additional emission leads to a good qualitative agreement between the Voyager 1 data and the model results.CNES; Russian Science Foundation (RSF) [14-12-01096]; Russian Foundation for Basic Research (RFBR) [16-52-16008-CNRS-a]6 month embargo; published online: 11 November 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu