The Voyager probes became the first two spacecraft from Earth to travel beyond the heliosphere and reach the interstellar medium. Voyager 1 did it first in 2012 and Voyager 2 made it in 2018.
Now data sent back from the twin probes suggest that the heliopause – the place where the heliosphere meets the interstellar medium – changes shape in unexpected ways. The Voyager probes and Interstellar Boundary Explorer (IBEX) satellite previously returned data suggesting that the heliopause changes as the heliosphere and the interstellar medium push against one another.
About the Heliosphere
The heliosphere is a “bubble” created by solar wind that separates the interstellar medium from most of the solar system. The relative motion between the interstellar medium and our solar system makes it look like a giant wind sock.
When Voyager crossed into the interstellar medium, it was 120 astronomical units (AU) from Earth, or about 120 times as far from Earth as the average distance between Earth and the Sun. The theoretical Oort Cloud is about 2000 AUs from Earth.
ENAs Produce Better Picture of the Heliosphere
IBEX can map the shape of the heliosphere by observing energetic neutral atoms (ENAs) produced by interactions between the heliosphere and interstellar medium at the heliopause. ENAs travel into the solar system from beyond Pluto’s orbit and can take up to eleven months to reach the vicinity of Earth.
IBEX’s first map of the heliosphere turned up surprising results like a bright ribbon that seems to wander around the heliopause. Scientists say this ribbon could provide clues about the direction of the interstellar magnetic field – a magnetic field that exists outside the heliosphere.
Now that the Voyager probes are outside the heliopause, IBEX can work together with them to study the changing shape of the heliosphere. Scientists say it’s a bit of process, especially with the Voyagers only providing two points at which readings can be taken “on site.”
“The Voyager spacecraft provide the only direct, in situ measurement of the locations of these boundaries. But only at one point in space and time,” Eric Zirnstein, a space physicist at Princeton University, explained to media outlets.
New Data Makes Models Obsolete
Scientists used data from IBEX to create models describing how the heliosphere might change shape. Now they might have to throw out those models and start over. Upon closer inspection of data on IBEX’s 2014 observations of ENAs, a research team noticed unexpected asymmetries in the heliosphere – ones that didn’t match the models.
Data from Voyager 1 and Voyager 2 confirmed that the heliosphere can change dramatically in a short period of time. This explains why there was a six-year gap between the two probes’ transit of the heliopause.
Voyager 1 especially returned interesting data implying a magnetic “foam” near the edge of the heliosphere, as seen in the below video.
A paper published in Nature Astronomy called the results “intriguing and potentially controversial.” The research paper’s authors plan to continue studying the heliosphere’s boundary with newer instruments like the Interstellar Mapping and Acceleration Probe (IMAP), which can detect ENAs. IMAP is slated to launch in 2025.