Our sun and all its planets travel through the Milky Way surrounded by a heliosphere, a bubble of charged particles that form the solar wind and which flows outward from the sun, engulfing the entire solar system.
While this sun-fueled encasing bubble is strong enough to keep out small interstellar debris coming our way, the sun’s influence only reaches so far. Which is why, for the last few decades, scientists have theorized that the outer boundary of our solar system is made up of a vast “hydrogen wall” — a threshold beyond the sun’s influence where galactic debris piles together, encircling our planets and everything in between them.
This buildup of interstellar matter includes not only dust particles too small to pierce through the giant bubble of solar wind, but also uncharged hydrogen atoms, which scatter ultraviolet light in a very specific way, explains Live Science.
This UV light was first detected by NASA’s Voyager missions 30 years ago, which led to the speculation that there’s a “hydrogen wall” going all around the solar system.
The theory has now gained even more momentum, in light of a new study published this week in the journal Geophysical Research Letters. Based on the findings of NASA’s New Horizons mission, the research suggests that one of the spacecraft’s instruments has actually picked up more clues that the “hydrogen wall” could really be there.
According to the study, the New Horizons probe detected a strong front of UV light at the edge of our solar system, well above what should be there if there was no “hydrogen wall,” reports Science News.
“We’re seeing the threshold between being in the solar neighborhood and being in the galaxy,” study co-author Leslie Young, a scientist at the Southwest Research Institute in Boulder, Colorado, said in a statement.
.@NASANewHorizons is the first spacecraft to see this ultraviolet glow since @NASAVoyager. It may mark a spot beyond the edge of the solar system, where the sun's influence wanes. https://t.co/2pjIw0DKKr— Lisa Grossman (@astrolisa) August 9, 2018
The signal was recorded by New Horizons’ Alice instrument, an ultraviolet telescope that scanned the sky before the spacecraft’s historic flyby of Pluto in 2015 — which ended up uncovering the planet’s 50-mile long dunes are actually made out of methane, the Inquisitr reported earlier this year.
In total, Alice performed seven scans between 2007 and 2017 looking for UV signals and found enough to confirm the measurements made three decades before by the two Voyager spacecraft.
“Both sets of data are best explained if the observed ultraviolet light is not only a result of the scattering of sunlight by hydrogen atoms within the solar system, but includes a substantial contribution from a distant source,” shows the new study.
The researchers point out that “this distant source could be the signature of a “wall” of hydrogen, formed near where the interstellar wind encounters the solar wind,” or it could be coming from deeper in the galaxy.
New Horizon’s next stop is the icy world Ultima Thule in the Kuiper Belt, which the spacecraft is set to reach on New Year’ Day 2019, the Inquisitr previously reported. Once this task is behind it, the mission will carry on surveilling the UV emissions at the edge of the solar system for the next 10 to 15 years, and hopefully will figure out exactly what causes it.
“If the ultraviolet light drops off at some point, then New Horizons may have left the wall in its rear-view mirror. But if the light never fades, then its source could be farther ahead — coming from somewhere deeper in space,” explained study co-author Wayne Pryor of Central Arizona College in Coolidge.