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Drawing the boundary between our solar system and interstellar space for the first time

Drawing the boundary between our solar system and interstellar space for the first time

Using data from NASA’s IBEX satellite, scientists have created the first 3D map of the boundary between our solar system and interstellar space.

For the first time, the boundaries of the heliosphere have been drawn, giving scientists a better understanding of how the solar wind and the interstellar wind interact.

Dan Reisenfeld, Los Alamos National Laboratory scientist and lead author of the article, which was published in Astrophysical Journal of June 10, 2021. “But this is the first time we’ve actually been able to measure and map it in 3D.”

The heliosphere is a bubble created by the solar wind, a flow of protons, electrons, and alpha particles that extends from the Sun into interstellar space and protects Earth from harmful interstellar radiation.

Reisenfeld and a team of other scientists used data from NASA’s Interstellar Boundary Explorer (IBEX) satellite, which detects particles that come from the heliosphere, the boundary layer between the solar system and interstellar space. The team was able to map the boundaries of this region, an area called the heliopause. Here, the solar wind, rushing into interstellar space, collides with the interstellar wind pushing toward the sun.

The first 3D map of the boundary between our solar system and interstellar space, a region known as the heliosphere. Credit: Los Alamos National Laboratory

To make 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 map the heliosphere,” Risenfeld said.

They did this using the IBEX satellite’s measurement of neutral energy atoms (ENAs) that result from collisions between solar wind and interstellar wind particles. The intensity of this signal depends on the intensity of the solar wind hitting the heliosphere. When the wave hits the sheath, the number of antinuclear antibodies increases and IBEX can detect them.

“The solar wind signal sent by the Sun varies in intensity and forms a unique pattern,” Riesenfeld explained. IBEX will see the same pattern in the returning ENA signal, two to six years later, depending on the energy of the ENA and the direction IBEX is looking through the heliosphere. This time difference is how we found the distance from the ENA source area in a particular direction.”

They then applied this method to build a 3D map, using data collected over the course of an entire solar cycle, from 2009 to 2019.

“This way, we can see the boundaries of the heliosphere in the same way that a bat uses sonar” to see “cave walls,” he added.

The reason the signal takes so long to get back to IBEX is because of the large 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. The Reisenfeld map shows that the minimum distance from the Sun to the heliosphere is about 120 AU in the direction facing the interstellar wind, and in the opposite direction, covering at least 350 astronomical units, which is the specified distance for the sensing technology. For reference, the diameter of Neptune’s orbit is about 60 astronomical units.

Reference: “Ibex 3D Heliosphere Map” by Daniel B. Reisenfeld, Maciej Bezovsky, Herbert O, Justina M. Sokov, Alex Zimoreno and Eric J. Astrophysical Journal of.
DOI: 10.3847 / 1538-4365 / abf658

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