New Horizons launched with a singular purpose: scan the ninth planet up close for the first time ever. Pluto was the ninth planet when New Horizons launched in 2006, but it was just a dwarf planet when the probe got there in 2015. It was still an incredible moment for astronomers around the world, many of which are still analyzing the data New Horizons sent back. The probe wasn’t done, though. NASA redirected New Horizons deeper into the Kuiper Belt, and now it has detected something fascinating at the edge of the solar system. Out past the planets, asteroids, and even the comets of the Oort Cloud, there’s a wall of hydrogen.
Since New Horizons only conducted a flyby of Pluto, it made sense to continue on into the Kuiper Belt to look at other objects. NASA has decided on target for New Horizons, and it’s on track to reach an object called MU69 in several months. On the way there, New Horizons has been scanning space in the outer solar system. This is a rare opportunity, after all. No spacecraft has been out this far since the Voyager probes. Those probes detected what we believed to be a wall of hydrogen around the solar system, and now New Horizons has confirmation.
Using the spacecraft’s Alice UV spectrometer NASA has taken several readings from the edge of the solar system. By analyzing the change in the ultraviolet spectrum over time, scientists now believe New Horizons has confirmed the early observations made by Voyager 1 and 2. There’s a gigantic wall of hydrogen out there.
So, what is this wall? We call it “space,” but space isn’t completely empty. Even in between stars there are some stray atoms and bits of dust. Clouds of neutral hydrogen atoms float through interstellar space, but the sun can affect how they’re distributed. Our local star emits a continuous stream of charged particles, which we call the solar wind. This outward force expands into a “bubble” around the solar system. The neutral hydrogen near our solar system slows down when it hits the solar wind, causing the atoms to build up into a “wall” structure.
The researchers are fairly confident in their assessment of the hydrogen wall, but New Horizons will continue making occasional observations of the wall twice per year as it continues moving outward. There’s still an outside chance the ultraviolet light is coming from a distant galaxy, but future observations will help to confirm.
Now read: Unexpected, mysterious x-rays found emanating from Pluto, Pluto Has Dunes Made of Ice Instead of Sand, and Scientists Say Some Ultrahot Exoplanets Have Star-Like Atmospheres
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