Strange ripples detected at the edge of the solar system: ScienceAlert

The bubble of space that encases the solar system may curl up, at least sometimes.

Data from a spacecraft orbiting Earth revealed undulating structures in the termination shock and the sun’s mantle: shifting regions of space that define one of the boundaries between space within the solar system, and what is outside – interstellar space.

The results show that it is possible to get a detailed picture of the boundaries 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 is moving away from the sun and protecting the planets in our solar system from cosmic radiation.

There are many ways in which the Sun affects the space around it. One of these is the solar wind, a continuous, supersonic flow of ionized plasma. It explodes through the planets and the Kuiper Belt, eventually fading into the great interstellar void.

The point at which this flux drops below the speed at which sound waves can travel through the interstellar propagating medium is called the termination shock, and the point at which this flux is no longer strong enough to respond to the very slight pressure of interstellar space is the heliosphere.

Both Voyager probes have crossed the heliosphere and are, effectively, now navigating through interstellar space, providing us with the first in-situ measurements of this shifting frontier. But there is another instrument in Earth’s orbit that has been helping scientists map the heliosphere since it began operations in 2009: NASA’s Interstellar Boundary Explorer (IBEX).

IBEX measures energetic neutral atoms, which are created when the sun’s solar wind collides with the interstellar wind at the solar system’s boundary. Some of these atoms are flung away into space, while others are ejected to Earth. Once the power of the solar wind it produced is taken into account, Energetic neutral particles returning to our path can be used to map the shape of the boundary, such as cosmic echolocation.

Previous maps of heliosphere structure relied on long-range measures of the evolution of solar wind pressure and energetic neutral atom emissions, smoothing boundaries in both space and time. But in 2014, over a period of about six months, the dynamic pressure of the solar wind increased by about 50%.

A team of scientists led by astrophysicist Eric Zirnstein of Princeton University used this shorter-range event to get a more detailed snapshot of what the termination shock and the sun’s rupture would look like — and they found huge ripples, on the scale of tens of astronomical units (one AU is the average distance between the Earth and the Sun) .

3D restorations of solar shell shock and end shock, huge wrinkles appear
3D visualization of the terminus shock and the heliosphere, showing huge ripples on both surfaces. (Zirnstein et al., Nat. Astron., 2022)

They also conducted modeling and simulations to determine how these high pressure winds interact with the boundaries of the Solar System. They found that the pressure front reached the termination shock in 2015, sending a pressure wave through the area between the termination shock and the sun’s mantle known as the inner sun sheath.

At the solar barrier, the reflected wave travels backward, striking the incoming flow of charged plasma behind the pressure front, creating a storm of energetic neutral atoms that fills the inner heliosphere by the time the reflected wave returns to the termination shock.

The team’s measurements also show a large shift in distance to the heliosphere. Voyager 1 crossed the heliosphere in 2012 at a distance of 122 AU. In 2016, the team measured that the distance to the heliosphere in the direction of Voyager 1 was about 131 AU. At that time, the probe consisted of 136 astronomical units from the Sun, and was still in interstellar space, but behind it the heliosphere swells.

The team’s measurement of the sun’s mantle in the direction of Voyager 2 in 2015 was more complex: 103 AU, with a margin of error of 8 AU on either side. At the time, Voyager 2 was 109 AU from the Sun, which is still within the margin of error. It didn’t cross the sun barrier until 2018, at a distance of 119 AU.

Both measurements indicate that the shape of the heliosphere is changing, rather than insignificantly. It is not entirely clear why.

However, in 2025, a new probe will be sent into space to measure the emission of energetic neutral atoms at a higher resolution, and over a wider energy range. The team said this should help answer some vexing questions about the strange, invisible “wrinkled” bubble that protects our tiny planetary system from the exoticism of space.

The search was published in natural astronomy.

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