We need to go back in time, to 1977, when the internet was still a military experiment and the Walkman had not even been invented. That’s because it was in that year that NASA made a bold decision: they launched two probes into the unknown. You may already know them; they were named Voyager 1 and Voyager 2, and they had a clear mission: to explore the far reaches of our Solar System and, if possible, look beyond. 50 years later, these probes are still working, and the greatest discovery may have happened only after they left our solar backyard.
Where does the solar system end?
Have you ever stopped to think about where the Solar System ends? Well, the answer depends on who asks… Some would even say it ends after Neptune, while others would say it’s in the distant Oort Cloud, where comets sleep. However, NASA chose a more interesting definition:
“The point at which the solar wind loses its strength and the domain of interstellar space begins. This point is called the heliopause”
The Sun emits a constant wind of charged particles, and this wind, known as the solar wind, forms a bubble around our solar system, called the heliosphere. Within it, it’s as if we were under the “protection” of the Sun. Now, beyond it, another world begins: we’re talking about a space where the rules change, the radiation is different, and the magnetic fields follow different laws. And it is there, at the border between the solar wind and the interstellar wind, that the Voyagers arrived.
Inside the 90,000ºF wall of fire
And it was only after the probes crossed this heliopause that something completely unexpected happened. Voyager 1 was the first to cross the boundary. Six years later, it was Voyager 2’s turn. And both, at different times, reported the same thing: they passed through a region of extreme temperatures, between 54,000 and 90,000 ºF. It’s an area so hot it became known as the wall of fire.
“With Voyager 1, scientists had only one sample of these magnetic fields and couldn’t say for sure whether the apparent alignment was characteristic of the entire exterior region or just a coincidence. Voyager 2’s magnetometer observations confirm the Voyager 1 finding and indicate that the two fields align”, NASA said
Don’t worry: this doesn’t mean the spacecraft caught fire or passed through a real furnace (especially after NASA resurrected Voyager 1). That’s because this “wall” isn’t solid, nor is it flaming. It’s a concentration of extremely energetic particles, whose density is so low that the heat doesn’t even conventionally reach the objects. Still, the phenomenon was so unexpected, and with such extreme values, that scientists wondered how something like this could go unnoticed for so long.
NASA already has new challenges
And as if the absurd heat detected wasn’t enough, the Voyagers brought yet another intriguing revelation. After crossing the wall, the sensors began to detect the behavior of the interstellar magnetic field. The surprise? It appeared to be aligned with the heliosphere’s internal magnetic field. Until now, it was thought that the outside followed its own rules, unconnected to the “inside”. So the questions arise:
- Is there a continuity between the two environments?
- Does the Sun’s influence extend further than we imagined?
- Is there a natural symmetry in galactic magnetic fields that we don’t understand?
It’s worth remembering that all these questions, once unthinkable, are now on scientists’ tables. And all thanks to these two probes that continue sending data, even though they’re more than 20 billion kilometers from Earth. In fact, they haven’t stopped there; recently, Voyager 1 intercepted a signal in space that came from 25 billion kilometers away.
