Voyager spacecraft crossed 'wall of fire' to reach interstellar space. What is it?

The Voyager spacecraft - 1 and 2 - are deep in interstellar space. But there was a time when scientists weren't sure whether they would be able to penetrate the "wall of fire" at the edge of space. The probes were launched in 1977 and were meant to study the Sun's heliosphere at the edge of the solar system.

Where does the solar system end?

It could either be termed as the point where the planets end, or the point to which the Sun's magnetic field spreads.

There is a point in space where a giant bubble shrouds the Sun and its planets. NASA says that this happens because of the "constant flow of charged particles called the solar wind" emitted by the sun, which "ultimately travels past all the planets to some three times the distance to Pluto before being impeded by the interstellar medium." The resultant bubble forms the heliosphere.

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From this point begins the heliopause, the edge of the heliosphere. "The boundary between solar wind and interstellar wind is the heliopause, where the pressure of the two winds is in balance," NASA states.

When the Voyager probes reached this point, they encountered temperatures of 54,000-90,000 degrees Fahrenheit. Could they pass it?

This place is called "the wall of fire" because of the intense heat. But both Voyagers managed to survive and cross into interstellar space despite the presence of extremely energetic particles. However, they weren't enough in numbers to cause a collision and transfer heat to the Voyagers.

While Voyager 1 went beyond the heliosphere on August 25, 2012, Voyager 2 crossed over to the other side in 2018.

Scientists were also able to learn that the heliopause is not static. As the "solar wind turns back and flows down the tail of the heliosphere," the heliopause expands and contracts. This was proved because the Voyager spacecraft reached the "wall of fire" at different distances from the sun.

Voyager 1 and Voyager 2 are still going strong years after they were supposed to end their missions. The former is expected to send data till 2030 and the latter well into the 2030s.