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In a monumental example of NASA's ongoing solar cartography efforts, the boundary of the sun's mysterious heliosphere has finally been mapped in 3D for the first time ever, providing a wealth of new insights as to how solar and interstellar winds intersect and interact.
Astronomers accomplished this breakthrough feat by employing data derived from NASA’s Interstellar Boundary Explorer (IBEX) spacecraft to determine the boundaries of our home star's heliosphere, that bubble of charged particles encircling the sun.
The informational image below represents that vast region of space enveloping the Solar System that is rich with solar winds and forms the border between the heliosphere (in brown) and interstellar space (in dark blue).
To achieve this task, NASA's Earth-orbiting IBEX satellite detects particles that emerge from the sun's heliosheath, which can then be recorded and labeled. Led by Dr. Dan Reisenfeld of the Los Alamos National Laboratory, this endeavor forced Reisenfeld and his colleagues to dissect IBEX data to chart the edges of this cosmic zone known as the heliopause.
At this juncture, solar winds muscle their way out toward interstellar space where they collide with the interstellar wind, which has an entirely different dynamic and actually pushes in towards the Sun. Researchers were able to quantify these measurements by harnessing echolocation properties similar to those sonar-type skills used by bats.
“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,” Dr. Reisenfeld explained in an official Los Alamos press release.
This study was published in the June 10, 2021 issue of the Astrophysical Journal Supplement Series. It was performed using the IBEX satellite’s measurement of energetic neutral atoms (ENAs) that are the inevitable result of violent collisions between solar wind particles and elements blasted out by the interstellar wind.
The intensity of that signal depends on the severity of the solar wind that pummels the heliosheath. When waves strike the sheath, the ENA count rises and IBEX can record it.
“The solar wind signal sent out by the Sun varies in strength, forming a unique pattern,” Dr. Reisenfeld adds. “IBEX will see that same pattern in the returning ENA signal, two to six years later, depending on ENA energy and the direction IBEX is looking through the heliosphere. This time difference is how we found the distance to the ENA-source region in a particular direction.”
These sonar-like methods were relied upon by Reisenfeld and his team to construct their 3D map using info gathered over a ten-year solar cycle from 2009 through 2019.
“In doing this, we are able to see the boundary of the heliosphere in the same way a bat uses sonar to ‘see’ the walls of a cave,” Dr. Reisenfeld said. “The reason it takes so long for the signal to return to IBEX is because of the vast distances involved.”
The new Los Alamos 3D map reveals that the minimum distance from the Sun to the heliopause is approximately 120 AU (astronomical units) when facing the interstellar wind, and extends a minimum of 350 AU in the opposite direction, which also represents the distance limit for this sounding technique.
“Physics models have theorized this boundary for years,” noted Dr. Reisenfeld. “But this is the first time we’ve actually been able to measure it and make a 3D map of it.”