"There's a "hydrogen wall" at the edge of our solar system, and NASA scientists think their New Horizons spacecraft can see it."
https://www.livescience.com/63297-hydrogen-wall-glowing-interstellar-space.html
"First detected in 1992 by the two Voyager spacecraft, the hydrogen wall has been theorized to exist at the very edge of the heliosphere. This bubble-like region of space is composed of cosmic rays — solar wind particles emanating from the sun. This is proven through data the Voyager spacecrafts are sending back to NASA. Currently, Voyager 2 is measuring an increased rate of these rays as it approaches the outer boundary of the heliosphere."
https://www.treehugger.com/hydrogen-wall-solar-systems-edge-nasa-4867820
"Scientists writing in Geophysical Research Letters think the probe may have caught a glimpse of an enormous wall of hydrogen sitting at the edge of our space neighborhood.
The craft's "Alice" UV spectrometer has detected an ultraviolet glow, which researchers think may be coming from this glut of hydrogen"
https://www.newsweek.com/what-hydrogen-wall-mysterious-structure-nasa-spotted-edge-solar-system-1077692
89,000°F Wall of Plasma Surrounds Our Solar System
https://nerdist.com/article/89000f-wall-of-plasma-solar-system/