  Recent observations of interplanetary medium (IPM) atomic hydrogen
Lyman-{\alpha} (Ly{\alpha}) emission in the outer solar system, made with the
Alice ultraviolet spectrograph on New Horizons (NH), are presented. The
observations include regularly spaced great-circle scans of the sky and pointed
observations near the downstream and upstream flow directions of interstellar H
atoms. The NH Alice data agree very well with the much earlier Voyager UVS
results, after these are reduced by a factor of 2.4 in brightness, in
accordance with recent re-analyses. In particular, the falloff of IPM
Ly{\alpha} brightness in the upstream-looking direction as a function of
spacecraft distance from the Sun is well-matched by an expected 1/r dependence,
but with an added constant brightness of ~40 Rayleighs. This additional
brightness is a possible signature of the hydrogen wall at the heliopause or of
a more distant background. Ongoing observations are planned at a cadence of
roughly twice per year.
