New Horizons probe spots possible wall of hydrogen at the edge of the solar system

Aug. 10 (UPI) -- New Horizons' data suggests a wall of hydrogen marks the edge of the solar system, where the sun's solar winds peter out, no longer able to push back interstellar winds.

As these two opposing winds butt up against each other, scientists believe hydrogen accumulates in a wall-like structure.

"We're seeing the threshold between being in the solar neighborhood and being in the galaxy," Leslie Young, astronomer at the Southwest Research Institute in Boulder, Colorado, told ScienceNews.

For the last several years, NASA's New Horizons probe has been speeding toward the outer limits of the solar system. Along the way, it's been regularly scanning the sky with its Alice ultraviolet spectrograph. The instrument's newest observations suggest the presence of massive wall of hydrogen.

The ultraviolet observations are similar to those made by the Voyager spacecraft some 30 years ago.

Hydrogen from within the solar system can't explain ultraviolet signature alone, suggesting a secondary source. Scientists believe the secondary source is the interstellar medium, matter from the Milky Way beyond, pushing in on the small cosmic bubble carved out by our sun's energy.

"This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant background," researchers wrote in a new paper, published this week in the journal Geophysical Research Letters.

New Horizons will continue to scan the sky twice a year with its Alice spectrograph. As it gets farther away from the sun and closer to the edge of the solar system, more accurate observations will allow scientists to confirm the presence of a hydrogen wall.

It's possible, scientists acknowledged, that the unique ultraviolet signature is the result of a source beyond the edge of the solar system.

Wayne Pryor of Central Arizona College told ScienceNews that if the ultraviolet signal begins to fade, then researchers can assume the New Horizons probe has broken through the wall. However, if it fails to dissipate, it's possible the signature is coming from a source even farther away.