Voyager 1: Still Exploring Interstellar Space After 47 Years

Launched in 1977, Voyager 1, humanity’s farthest-traveling emissary, continues its remarkable journey through interstellar space. After more than four decades of exploration, the spacecraft remains a testament to human ingenuity and a vital source of data about the uncharted regions beyond our solar system. Currently located over 164 astronomical units (AU), or more than 24 billion kilometers, from Earth, Voyager 1 entered interstellar space in 2012, marking a significant milestone in space exploration.

A Mission of Discovery

Originally designed for a four-year mission to explore Jupiter and Saturn, the Voyager program, consisting of Voyager 1 and its twin, Voyager 2, far exceeded expectations. Voyager 1 provided unprecedented close-up images and data about these gas giants, revealing details about their atmospheres, magnetic fields, and moons. Voyager 2, launched shortly before Voyager 1, followed a different trajectory, also visiting Uranus and Neptune, becoming the only spacecraft to ever explore these ice giants.

The “Grand Tour” accomplished, Voyager 1 embarked on a new phase of its mission: the long journey out of the heliosphere, the bubble of solar wind and magnetic field created by the Sun.

Entering Interstellar Space

The precise moment Voyager 1 crossed into interstellar space was a subject of scientific debate for some time. While the spacecraft had been venturing further into the outer reaches of the solar system, definitive evidence of crossing the heliopause – the boundary between the heliosphere and interstellar space – was elusive. In 2012, scientists observed a significant and sustained change in the plasma environment surrounding Voyager 1, providing compelling evidence that it had indeed entered interstellar space. This was confirmed by the sudden drop in solar particles and a corresponding increase in galactic cosmic rays.

“These observations provided irrefutable evidence that Voyager 1 had finally broken free from the Sun’s influence and was navigating through the plasma of interstellar space,” stated Dr. Ed Stone, Voyager project scientist at Caltech, in a 2013 NASA press release.

Continuing to Send Data

Despite its age and vast distance, Voyager 1 continues to transmit valuable data back to Earth. Powered by a radioisotope thermoelectric generator (RTG), which converts the heat from decaying plutonium into electricity, the spacecraft still has enough power to operate some of its scientific instruments. These instruments are providing unique insights into the composition, density, and magnetic field of the interstellar medium.

However, the RTG’s power output is steadily decreasing, forcing engineers to carefully manage the spacecraft’s resources. Over the years, instruments have been selectively turned off to conserve power, extending the mission’s lifespan. It is anticipated that Voyager 1 will eventually cease transmitting data sometime in the 2020s as its power source diminishes further.

The Golden Record

Attached to Voyager 1 (and Voyager 2) is a golden record, a phonograph record containing sounds and images selected to portray the diversity of life and culture on Earth. Intended as a message to any extraterrestrial civilization that might encounter the spacecraft in the distant future, the golden record includes greetings in multiple languages, sounds of nature, music from various cultures, and images depicting human life and the planet Earth.

The golden record serves as a symbolic gesture, representing humanity’s hope for future contact and a lasting legacy of our presence in the cosmos.

A Legacy of Exploration

Voyager 1’s journey represents a remarkable achievement in space exploration. Its continued operation and data transmission, even after decades of travel, demonstrate the enduring power of human innovation. As Voyager 1 continues its voyage through interstellar space, it will undoubtedly continue to provide invaluable data and inspire future generations of scientists and explorers.

The Voyager mission stands as a testament to the enduring human spirit of exploration, pushing the boundaries of our knowledge and expanding our understanding of the universe.

After entering interstellar space in 2012. Since then, its Plasma Wave System (PWS) instrument has revealed unexpected ongoing activity in the interstellar medium.One of the key discoveries is a persistent, very faint emission of narrowband plasma waves—often popularly described as a low-frequency “cosmic hum” or faint drone—detected nearly continuously since around 2017.These are weak electron density oscillations in the range of about 2–3 kHz (far below human hearing), distinct from occasional stronger plasma waves triggered by solar coronal mass ejections.Key points:The emissions are extremely low amplitude but persistent, enabling high-resolution mapping of interstellar plasma density variations on scales as small as ~0.03 AU over distances of tens of AU.

They reveal small-scale density fluctuations and mild turbulence in the very local interstellar medium, independent of solar influence.Likely driven by thermal or quasi-thermal noise in the plasma, rather than dramatic events.

This persistent signal shows that the interstellar medium is more dynamically active at low levels than previously assumed, providing a new, continuous probe of its density, structure, temperature, and magnetic field properties.Primary reference: Ocker, S.K., Cordes, J.M., Chatterjee, S. et al. Persistent plasma waves in interstellar space detected by Voyager 1. Nature Astronomy 5, 761–765 (2021). Nearly half a century after launch, Voyager 1 continues to deliver groundbreaking insights into the space beyond our solar system.