The outer boundary of the heliosphere, an enormous protective bubble near the edge of the solar system, has been mapped for the first time by a group of scientists from Los Alamos National Laboratory (LANL), a press statement reads.
In order to compile the map, the scientists utilized data collected over an entire solar cycle between 2009 and 2019 by NASA's Interstellar Boundary Explorer (IBEX) satellite, which orbits the Earth. Their work is detailed in the Astrophysical Journal.
That satellite was specifically launched so as to investigate the interaction between the interstellar medium and solar winds near the edge of our solar system, made up of protons, electrons and alpha particles.
The outer boundary layer mapped by the LANL scientists, called the heliopause, was recently found to be shaped somewhat like a croissant by another study using data from NASA's Voyager 1 probe. It has long been known that this outer boundary protects us from harmful interstellar radiation that would otherwise reach Earth.
For the LANL map, the researchers utilized data from the IBEX satellite, which detected particles called energetic neutral atoms (ENAs) — a byproduct of collisions between our Sun's solar wind and interstellar wind. The stronger the solar wind as it collides with the interstellar medium, the higher the count of ENAs.
"The solar wind 'signal' sent out by the Sun varies in strength, forming a unique pattern," said Dan Reisenfeld, lead author on the paper.
"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," Reisenfeld continued.
Bat-like method maps the outer reaches of the solar system
The scientists compare their utilization of solar wind measurements to map the heliosphere to the way bats use sonar to map their immediate surroundings.
"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," Reisenfeld explained.
The new map constitutes the first time that a three-dimensional map has been made of the heliosphere — physics models had previously only theorized the boundary on the outer edges of our solar system.
The new map allows for measurements of the real thing made in astronomical units (AU), with one AU constituting the distance between the Earth and the Sun.
The map shows that the shortest distance between the Sun and the heliopause, which goes in the direction facing the solar wind, is about 120 AU. The longest distance extends at least 350 AU, which is as far as NASA's IBEX satellite detection system can reach.