The bubble of space encasing the Solar System might be wrinkled, at least sometimes.
Data from a spacecraft orbiting Earth has revealed ripple structures in the termination shock and heliopause: shifting regions of space that mark one of the boundaries between the space inside the Solar System, and what’s outside – interstellar space.
The results show that it’s possible to get a detailed picture of the boundary of the Solar System and how it changes over time.
This information will help scientists better understand a region of space known as the heliosphere, which pushes out from the Sun and shields the planets in our Solar System from cosmic radiation.
There are a variety of ways the Sun affects the space around it. One of those is the solar wind, a constant supersonic flow of ionized plasma. It blows out past the planets and the Kuiper Belt, eventually petering out in the great emptiness between the stars.
The point at which this flow falls below the speed at which sound waves can travel through the diffuse interstallar medium is called the termination shock, and the point at which it is no longer strong enough to push back against the very slight pressure of interstellar space is the heliopause.
Both Voyager probes have crossed the heliopause and are, effectively, now cruising through interstellar space, providing us the first in situ measurements of this shifting boundary. But there’s another tool out in Earth orbit that has been helping scientists map the heliopause since it commenced operations in 2009: NASA’s Interstellar Boundary Explorer (IBEX).
IBEX measures energized neutral atoms, which are created when the Sun’s solar wind collides with the interstellar wind at the Solar System boundary. Some of those atoms are catapulted further out into space, while others are flung back at Earth. Once the strength of the solar wind that produced them is taken into account, energized neutral particles that return our way can be used to map the shape of the boundary, a bit like cosmic echolocation.
Previous maps of the structure of the heliosphere have relied on long-scale measures of the evolution of solar wind pressure and energetic neutral atom emissions, which resulted in a smoothing of the boundary in both space and time. But in 2014, over a period of roughly six months, the dynamic pressure of the solar wind increased by roughly 50 percent.
A team of scientists led by astrophysicist Eric Zirnstein of Princeton University has used this shorter-scale event to obtain a more detailed snapshot of the shape of the termination shock and heliopause – and found huge ripples, on the scale of tens of astronomical units (one astronomical unit is the average distance between Earth and the Sun).
We also performed modeling and simulations to determine how this high-pressure wind interacts with the solar system boundaries. They found that the 2015 pressure front reached the terminal shock and sent pressure waves to the region between the terminal shock and the heliopause, known as the inner heliosheath.
At the heliopause, the reflected wave returns and collides with the still-inflowing charged plasma behind the pressure front, creating a storm of energetic neutral atoms that fills the inner helices when the reflected wave returns to the terminal impact. increase.
The team’s measurements also show that the distance to the heliopause varies quite clearly. Voyager 1, in 2012 she passed the heliopause at a distance of 122 AU. In 2016, the team measured the distance to the heliopause to Voyager 1 to be about 131 astronomical units. At that time, the probe was at a distance of 136 AU from the Sun, still in interstellar space, but beyond which the heliosphere was bulging.
Measuring the team to the heliopause for Voyager 2 in 2015 is a little more complicated.103 AU, on either side he has an error of 8 AU. At this point, Voyager 2 is at her 109 AU distance from the Sun, which is still within error. Only in 2018 did he pass the heliopause at his 119 AU distance.
Both measurements show that the shape of the heliopause is changing, and that change is insignificant. The reason is not entirely clear.
But in 2025, a new probe will be launched to measure emissions from energetically neutral atoms more precisely and over a wider energy range. According to the team, it should help answer some thorny questions about the strange, invisible “wrinkled” bubbles that protect our tiny planetary system from space oddities.