⇧ [VIDÉO] You might also like this partner content (post ad)
Launched in 2008, NASA’s Interstellar Boundary Explorer orbits Earth to map the heliopause, the boundary that separates our solar system from the interstellar medium. The data transmitted by this tiny satellite suggests that the edges of our solar system are the site of strange waves.
The Milky Way is home to over 100 billion stars. Our solar system is enclosed in a “bubble” called the heliosphere, which separates us from the rest of the galaxy and protects us from certain cosmic rays. This protective bubble is created by the Sun itself, which constantly emits a stream of charged particles. This solar wind extends far beyond Neptune and even beyond the Kuiper Belt, carrying a portion of the Sun’s magnetic field with it.
The heliosphere was discovered in the late 1950s. As scientists study it, they learn more about how it reduces the radiation exposure of astronauts and spacecraft, and more generally about how stars can affect their neighboring planets. Equipped with telescopes observing the outer edge of the heliosphere, the Interstellar Boundary Explorer (IBEX) captures and analyzes a class of particles called “energetic neutral atoms” (or ENA), which form where the interstellar medium and the solar wind meet – a region called the heliopause.
A limit explored thanks to the flow of atoms
All the major planets in our solar system are located in the innermost layer of the heliosphere, where the particles of the solar wind are extremely fast (moving about a million kilometers per hour). The outer boundary of this central layer is called the “terminal shock”; beyond this limit, the particles begin to slow down under the influence of the pressure of the external interstellar medium. The layer between the terminal shock and the heliopause is called the heliosheath.
The IBEX satellite captures ANEs created when the solar wind collides with the interstellar wind; if most of these atoms are then flung towards deep space, some of them float back towards the center of the solar system (and are thus captured by IBEX). Once the strength of the solar wind is taken into account, these particles can be used to map the shape of the boundary – in a way, a form of cosmic echolocation.
Maps of the heliosphere established so far have relied on long-scale measurements of the evolution of solar impact and ENA emissions. ” This required spatial and temporal averaging that smoothed out small or dynamic features of the heliosphere “, explain the researchers in Natural astronomy. However, in late 2014, the dynamic pressure from the solar wind increased by about 50% over a period of six months, causing a time-dependent and direction-dependent increase in the atomic fluxes.
A team of scientists, led by Princeton University astrophysicist Eric Zirnstein, used this event to get a more detailed snapshot of the shape of the terminal shock and the heliopause. Data collected by IBEX revealed enormous ripple structures on the scale of tens of astronomical units.
A “moving” boundary to the interstellar medium
Using simulations, the team found that the pressure front reached the terminal shock in 2015, sending a pressure wave through the heliosheath. Arriving at the heliopause, this wave was reflected, turned back toward the terminal shock, and then collided with the flow of charged plasma which followed the pressure front. Which caused a veritable storm of ENA in the heliosheath.
The team’s measurements also show a significant change in the distance to the heliopause. The Voyager 1 probe crossed the heliopause in 2012 at a distance of 122 AU. In 2016, the team measured the distance to the heliopause in the direction taken by Voyager 1 to be about 131 astronomical units (au); the probe was in interstellar space. Ditto for the Voyager 2 probe: when it crossed the heliopause in 2018, it was at a distance of 119 AU. But measurements made in 2015, in the direction of Voyager 2, had estimated the distance to the heliopause to be about 103 AU.
These findings suggest that the shape of the heliopause is changing significantly, but scientists do not yet know why.
In 2025, NASA is expected to launch the Interstellar Mapping and Acceleration Probe (IMAP). The ENA cameras on this vessel have a higher resolution and are more sensitive than those on IBEX. ” IMAP imagers will be able to produce full sky maps every 6 months and partial sky maps every 3 months, allowing us to quantify variability in the outer heliosphere at twice the speed of IBEX “, the researchers detail. According to them, this should solve some of the mysteries that still surround this strange bubble that protects our planetary system from space.