New Horizons Probe May Have Spotted a Wall of Hydrogen at the Edge of the Solar System

Monday, 13 August 2018 - 11:59AM
Space
Solar System
NASA
Monday, 13 August 2018 - 11:59AM
New Horizons Probe May Have Spotted a Wall of Hydrogen at the Edge of the Solar System
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Pixabay & NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Most people imagine space as a giant, empty void, but it turns out there's a lot more "stuff" floating around than we expected (including vast amounts of carbon-based "space grease"). One of the more interesting examples is an elusive wall of interstellar matter pressing at the boundaries of our solar system, whose supposed ultraviolet signal was picked up 26 years ago by one of the Voyager probes. Now, the New Horizons probe has a shot at putting an end to a long-standing mystery: what exactly is out there?

 

Thanks to New Horizons' "Alice" instrument, a combination UV telescope and spectrometer, the probe is able to get a much better picture of the persistent ultraviolet signal lurking at the edge of the solar system. Right now, scientists theorize that the signal comes from the dividing line between the heliosphere, a bubble of solar wind that stretches about 120 AU from the Sun, and the interstellar space beyond, which contains large amounts of uncharged hydrogen atoms. All this hydrogen is pressing inward against the faint currents of solar wind radiating outward, creating a wall of hydrogen that should scatter ultraviolet light in a specific way.  According to a new study published in Geophysical Research Letters, the light picked up by New Horizons is consistent with that pattern. According to Leslie Young of the Southwest Research Institute: "We're seeing the threshold between being in the solar neighborhood and being in the galaxy."

What makes this potentially groundbreaking is that getting a bead on the hydrogen wall will help astronomers and other scientists map out the fluctuating boundaries of the heliopause, the effective end of the Sun's influence. "It's really exciting if these data are able to distinguish the hydrogen wall," said David McComas of Princeton University. If the New Horizons spacecraft, which is still on its way out of the solar system, sees a drop in ultraviolet light on its instruments, it may indicate that it's passed through the hydrogen wall—otherwise, the ultraviolet light may be coming from something else, located deeper in space.

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