  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 (that is towards 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 modelling of these data is performed in the frame of a
state-of-art self-consistent kinetic-MHD model of the heliospheric interface
(Izmodenov & Alexashov, 2015). 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 non-heliospheric Lyman $\alpha$ component, which could be
galactic or extragalactic. Our parametric study shows that $\sim$25 R of
additional emission leads to a good qualitative agreement between the Voyager 1
data and the model results.
