Scientists first mapped the edge of the solar system (called the heliosphere) using a technique similar to echolocation.

The solar wind forms a huge protective bubble around the solar system, which repels 70% of the cosmic radiation but does not protect all sides equally. Because of this, it looks like a drop at the edges. Scientists figured this out by making a 3D map of the solar system.

The bubble itself is known as the heliosphere, and its edge is the heliopause. If we move from the Sun, then at some distance there comes a moment when the pressures of these two colliding streams – the solar wind from the inside and the interstellar plasma from the outside – equalize. It is in this place that the heliopause is formed, and the space inside it is called the heliosphere.

Unlike most borders on Earth, scientists have no idea how big this border is or what it might look like. A new study published in The Astrophysical Journal describes the creation of the first three-dimensional map of the heliosphere.

Using 10-year data from NASA’s Interstellar Boundary Explorer satellite, the study’s authors tracked solar wind particles as they travel from a star to the edge of the heliosphere and back. So the team calculated how far the wind blew them in a given direction before it was reflected by interstellar radiation. In turn, this allowed scientists to map the edges of the solar system in a similar way to how bats use echolocation.

“Just as bats send sonar pulses in all directions and use the return signal to create a mental map of their surroundings, we used the solar wind from all directions to map the heliosphere,” the scientists explain.

As can be seen on the group’s map, the heliosphere does not quite match the “spherical” part of its name. The barrier around the solar system is more like a wobbly blob, which is much thinner on one side than on the other.