NASA/IBEX/Adler Planetarium

A diagram of our heliosphere. For the first time, scientists have mapped the heliopause, which is the boundary between the heliosphere (brown) and interstellar space (dark blue).

For the first time, the boundary of the heliosphere has been mapped, giving scientists a better understanding of how solar and interstellar winds interact.

"Physics models have theorized this boundary for years," said Dan Reisenfeld, a scientist at Los Alamos National Laboratory and lead author on the paper, which was published in the Astrophysical Journal. "But this is the first time we've actually been able to measure it and make a three-dimensional map of it."

The heliosphere is a bubble created by the solar wind, a stream of mostly protons, electrons, and alpha particles that extends from the sun into interstellar space and protects the earth from harmful interstellar radiation.

Reisenfeld and a team of other scientists used data from NASA's earth-orbiting Interstellar Boundary Explorer (IBEX) satellite, which detects particles that come from the heliosheath, the boundary layer between the solar system and interstellar space. The team was able to map the edge of this zone -- a region called the heliopause. Here, the solar wind, which pushes out toward interstellar space, collides with the interstellar wind, which pushes in toward the sun.

To do this measurement, they used a technique similar to how bats use sonar.

"Just as bats send out sonar pulses in every direction and use the return signal to create a mental map of their surroundings, we used the sun's solar wind, which goes out in all directions, to create a map of the heliosphere," said Reisenfeld.

The reason mapping took so long is because of the vast distances involved. Distances in the solar system are measured in astronomical units (AU) where 1 AU is the distance from the earth to the sun. Reisenfeld's map shows that the minimum distance from the sun to the heliopause is about 120 AU in the direction facing the interstellar wind operated by Triad National Security, LLC for the National Nuclear Security Administration, and in the opposite direction, it extends at least 350 AU, which is the distance limit of the sounding technique.

For reference, the orbit of Neptune is about 60 AU across.

-- Staff Report

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