Spanning billions of miles, how did this pair of "twins" knock on the "door" to interstellar space?

Author: Huang Xianghong Duan Yuechu

In mankind's long journey of exploration of the universe, there is a pair of shining "twin stars" - NASA's Voyager probes. They are like fearless pioneers, crossing billions of miles, revealing a corner of the mysterious veil of the edge of the solar system and interstellar space for us, and completely changing our understanding of the boundaries of the universe.

An article written by Meghan Bartels and published in Scientific American magazine on December 13, 2024, tells the legendary story of Voyager in depth. The Voyager probe is ingeniously designed, with a cylindrical main structure and equipped with a variety of powerful instruments and equipment. They are equipped with high-precision optical cameras that can capture clear images of distant celestial bodies, allowing us on Earth to witness the magnificent rings and mysterious satellites of the outer planets. The probe is also equipped with an advanced spectrometer. By analyzing the spectrum of light emitted by celestial bodies, scientists can understand the chemical composition and physical properties of these celestial bodies, and thus infer their formation and evolution. In addition, Voyager also carries particle detectors to measure solar wind particles and high-energy particles in interstellar space. These data are crucial for studying the origin and propagation of cosmic rays.

Since they set out on their journey in 1977, the twin probes have been tasked with exploring the outer planets. They have flown past Jupiter and Saturn, and Voyager 2 has also visited Uranus and Neptune, sending back precious images and data of these distant giant planets, allowing us to get a close look at the true face of these mysterious worlds for the first time.

However, their mission did not end with the end of the exploration of the outer planets. When the planetary observation mission was completed, despite the aging of instruments and equipment and the gradual reduction of energy, NASA scientists decided to let Voyager continue to move forward and head towards the boundary of the solar system. During the long journey, Voyager went through several key stages. In December 2004, Voyager 1 arrived at the termination shock region, where the solar wind began to slow down sharply; in August 2012, it successfully crossed the heliopause and officially entered interstellar space. Voyager 2 followed closely behind, crossing the termination shock in 2007 and passing through another area of ​​the heliopause in November 2018.

These detection results are of great significance. From the perspective of scientific cognition, they make us realize that the heliosphere is not a simple, static boundary, but a complex, changeable and dynamic region. The interaction between the solar wind and the interstellar medium presents an amazing sight here. For example, in the heliosheath region between the termination shock and the heliopause, the motion state of solar matter changes dramatically, slowing down or even flowing in the opposite direction. Moreover, the 11-year cycle of solar activity is like the pulse of the universe, which profoundly affects the size and shape of the heliosphere, causing it to expand and contract periodically. This phenomenon is clearly reflected in the data collected by the detector.

The Voyagers have also slightly unveiled the mystery of interstellar space. There is a completely different environment from the inner solar system, filled with galactic cosmic rays and dust from the death of ancient stars. These discoveries have given us a deeper understanding of the evolution of the universe and the distribution of matter, as if they have opened a door to the deep history of the universe for us, allowing us to peek into those distant and ancient stories.

Experts spoke highly of the results of Voyager. Merav Opher, a space physicist at Boston University, said with emotion: "We always thought we knew a lot about the heliosphere, but after Voyager's journey, we found that what we knew was just the tip of the iceberg. Its complexity and dynamics are far beyond imagination. This also makes us understand that there are still too many mysteries in the universe waiting for us to explore." Jamie Rankin of Princeton University also pointed out: "Before Voyager broke through the heliosphere, the observations we made on Earth were actually interfered and filtered by the various layers of the sun. Now the data they send back are like pure information from the depths of the universe, providing us with a new research perspective and giving us a clearer understanding of the relationship between the sun and the universe."

But the Voyagers' exploration was not smooth sailing, and they also left many unsolved mysteries. For example, one of the probes experienced a strange phenomenon of crossing the termination shock wave many times, and the reason behind this is still debated by scientists. Moreover, there is no definite answer to what the overall shape of the heliosphere is. It may be like a comet with a long tail, or like a curved croissant, or even a shape we have never imagined.

Despite this, the value of Voyager is irreplaceable. They are like messengers in the universe, bringing us precious information from distant stars, inspiring countless people's yearning for and desire to explore the universe. Although their instruments will stop working one day, the exploration journey they have opened will be forever engraved in the long history of human exploration of the universe, inspiring generations of scientists to move forward courageously, to pursue the endless sea of ​​stars, and to strive to piece together a complete and magnificent picture of the universe.

References:

NASA's Beloved Voyager Probes Find Puzzles beyond the Solar System｜Scientific American