The Sun's Pulse in Interstellar Silence express
Two aging spacecraft, launched back in 1977, are flying through interstellar space — the region where the Sun's influence fades. The Sun doesn't just shine; it continuously blows a stream of charged particles that forms a giant bubble around our system — the heliosphere. Beyond its boundary, at about 150 astronomical units (one AU is the distance from Earth to the Sun), Voyager 1 felt a strange jolt. In 2020, its instruments recorded a sharp rise in the magnetic field, followed by a long "hump" and an enhanced field lasting months.
Scientists built a computer model that mimics the solar wind's behavior and its collision with the interstellar medium. It turned out that the jolt was a compression wave born from the Sun itself. Our star lives on an 11-year cycle: it calms down, then stirs with sunspots and flares. As activity ramps up, the solar wind becomes denser and faster, and this wave, like a slow drumbeat, travels all the way to the heliosphere's edge. When it hits, it compresses the interstellar gas and magnetic field — exactly what Voyager 1 felt.
Analysis of turbulence, small chaotic fluctuations in the field, showed that they fade with distance. Up to 165 astronomical units, pulsations with periods shorter than 10 days are still noticeable, but very short bursts (under an hour) nearly vanished after 2022. This doesn't mean the medium changed; it's just that the wave weakened, like ripples on a pond after a stone is thrown. Voyager 2, traveling in a different direction, is predicted to encounter several such waves by 2026, and then a powerful shock from the next solar cycle around 2030. The New Horizons spacecraft, now catching up, will cross the Sun's termination shock in 2031 at about 80 astronomical units.
Original abstract
as written by the authors arXiv:2602.10446
Voyager spacecraft (V1 and V2) provide unique in situ measurements of perturbations propagating beyond the heliopause through the very local interstellar medium (VLISM), including the shocks and pressure fronts whose origin is debated. In particular, a jump in magnetic field strength, observed by V1 in 2020.4 at 149.3 au from the Sun, was followed by a distinct "hump" and persistently strong magnetic field, both requiring theoretical explanation. This paper offers an interpretation of those observations using a self-consistent, MHD model of the solar wind - LISM interaction driven by the OMNI and interplanetary scintillation data combined with a turbulence analysis of Voyager data. Our simulations convincingly demonstrate that global, solar-cycle-driven compressions, on hitting the heliopause, can reproduce those puzzling V1 observations. They appear to be associated with solar cycle 24, whereas similar interstellar magnetic field structures can occur once per cycle. The turbulence analysis reveals time-dependent magnetic compressibility that persists up to 165 au at scales below 10 days. Turbulence intermittency at scales below 1 hour is mostly confined to specific intervals, possibly associated with a broad foreshock region. The apparent disappearance of intermittency since 2022 reflects the turbulence weakening rather than a fundamental change in VLISM properties. We predict that V1 will record relatively strong magnetic field strengths until $$\sim$$2030, followed by weaker, infrequent perturbations. At V2, we expect multiple solar-driven compressions before 2026, followed by a major event induced by solar cycle 25 around 2030. New Horizons is expected to cross the termination shock at 80$$\pm$$2 au in 2031.
Voyager 1 is currently more than 24 billion kilometers from Earth — a radio signal from it takes nearly a day to reach us.
In the film 'Star Trek: The Motion Picture', the Voyager probe becomes sentient and returns to Earth — real probes, for now, only send us signals from the dark.