The ultraviolet signal may mark a wall of hydrogen where the sun’s influence wanes
The New Horizons spacecraft has spotted an ultraviolet glow that seems to emanate from near the edge of the solar system. That glow may come from a long-sought wall of hydrogen that represents where the sun’s influence wanes, the New Horizons team reports online August 7 in Geophysical Research Letters.
“We’re seeing the threshold between being in the solar neighborhood and being in the galaxy,” says team member Leslie Young of the Southwest Research Institute, based in Boulder, Colo.
Even before New Horizons flew past Pluto in 2015 (SN: 8/8/15, p. 6), the spacecraft was scanning the sky with its ultraviolet telescope to look for signs of the hydrogen wall. As the sun moves through the galaxy, it produces a constant stream of charged