NASA’s Voyager 2 probe crossed into interstellar space in November 2018. Now, a year later, scientists have shared the latest data from the intrepid spacecraft, Gizmodo reports. The data is spread across five different papers published in the journal Nature Astronomy.
Voyager 2 is the second human-made object to leave the realm of the Sun’s influence, also called the heliosphere. The mysterious boundary where the heliosphere ends is called the heliopause.
In August 2012, Voyager 2’s sister spacecraft, Voyager 1, became the first human-made object to leave the solar system. While both spacecraft carry the same suite of instruments, they have sent back differing data thus far. Furthermore, they have experienced different treks through the solar system and beyond.
The Voyager Mission
Both spacecraft launched in 1977. Voyager 2 actually launched a few days before Voyager 1. However, the latter flew along a speedier trajectory so that it could rendezvous with Saturn’s moon Titan. While Voyager 2 didn’t get to explore the mysterious Titan, it was the only probe that cruised by the outer gas giants Uranus and Neptune.
The two probes gave humanity its first glimpse of the worlds in the outer solar system. After flying by, sending back photos and data on the gas giants, the Voyager probes continued on and eventually left the solar system. When Voyager 1 became the first to cross the heliopause in 2012, it also sent back humanity’s first readings on interstellar space. Even so, there was some data that Voyager 1 was not able to collect.
The Sun’s Final Frontier
While both spacecraft feature the same instruments, Voyager 1’s plasma detector stopped working in 1980. This made it difficult for researchers to tell just when it had crossed the heliopause. Measuring the transition from the Sun’s hotter, less dense plasma to the cooler, thicker plasma of interstellar space is the main indicator that a spacecraft has left the heliosphere. So, astronomers had to rely on Voyager 1’s other instruments to measure things like electron behavior and magnetic fields to confirm the crossing.
Now, Voyager 2’s plasma detector is still in commission over 40 years later. Since that system was still working when the probe crossed the heliosphere, it gathered data that Voyager 1 could not. This includes the first direct view of the plasma transition. It shows that a 20-fold increase in plasma density occurs at the heliosphere border. This reading confirmed what Voyager 1 scientists had inferred from the data that they did have.
Moreover, with two points of reference that were very far away from each other (think of two distant points on a circle), researchers could see that the distance of the heliopause is fairly consistent. Nonetheless, the probes did send back some conflicting readings. For instance, Voyager 2 saw changes in magnetic fields where Voyager 1 did not. Voyager 2 also detected more particles from the sun that had leaked out of the heliosphere.
So, there’s still a lot of questions out there. One interesting theory to explain the differences is that the heliopause has a tail like a comet. Hopefully, the Voyager probes will help us answer that question and others. Even though it’s now in its fifth decade, the Voyager Mission has proven that it’s still relevant.