Are humans the loneliest specks of dust in the universe? These romantic journeys in space exploration will tell you the answer

Whether you believe it or not, I firmly believe that there must be humans like us living in the depths of the distant universe. When we point our telescope at a corner of the sky, perhaps aliens are there, looking for us as well.

1. Where are they?

In the 1950s, physicist and Nobel Prize winner Enrico Fermi proposed a hypothesis: in the ancient and vast universe, if even a tiny fraction of the planets develop intelligent life, then there should be countless civilizations in the universe. So why haven't we observed other civilizations? Where are they? This is the famous Fermi paradox, also known as the "Fermi paradox."

As the exploration of the universe deepened, scientists also began to focus on the research and signal capture outside the solar system. In 1972 and 1973, the United States launched two planetary probes, Pioneer 10 and Pioneer 11. They were both equipped with a gold-plated aluminum plate, on which were printed information such as time and distance units, the position of the solar system in the universe, and the appearance and size of men and women. This can be regarded as the most representative "Earth business card" and the first time that humans placed a human information nameplate prepared for aliens on a probe.

It flew into the depths of the universe along with Pioneer 10 and 11, in the hope that one day aliens will discover it and use it to understand human intelligence.

Image credit: NASA

Although the probability is very small, humans seem to particularly like this romantic feeling, just like putting a bottle on the beach and letting it drift on the sea until the "right person" picks it up.

2. "Greetings from the children of planet Earth."

The year was 1977. The "geometric alignment" of the planets, which occurs only once every 176 years, gave humans a new idea about "drifting bottles"[1], and thus began a romantic exploration mission. NASA designed two identical spacecrafts, Voyager 1 and Voyager 2, and prepared a gold-plated copper disk record with a diamond phonograph needle inside, which meant that even after a billion years, the sound quality of the record would remain the same. The record contained the following information: 12 minutes of voice integration, including kisses, babies crying, etc.; greetings from various countries, including greetings from then UN Secretary-General Kurt Waldheim and then US President Carter; 116 photos, including human science, civilization and ourselves. The most interesting one was the brain waves from Ann Druyan, a team member who was still immersed in the sweetness of love at the time. It can be said that this brain wave recorded the most primitive romantic heartbeat that love brings to universal human beings. The album also records 90 minutes of music, including clips of Japanese dramas, Peruvian wedding songs, and classics by famous musicians such as Bach, Beethoven, and Mozart. It is worth mentioning that there is a Chinese guqin piece "Flowing Water". This ethereal Chinese music seems to depict a lonely traveler sailing in the vast sea of ​​stars, hoping that some intelligent creatures can discover it and unravel its secrets. This corresponds exactly to the scene of "seeking a soulmate in the mountains and flowing water".

Voyager 1 is launched on a rocket. Image credit: NASA

The Voyager 2 probe's journey began on August 20, 1977, 16 days after Voyager 1 was launched. In March 1979, it made a close visit to Jupiter; in November 1980, it made a close visit to Saturn... They achieved one miraculous success after another in their flights. Beyond the initial project plan, the engineers and scientists participating in this mission team are doing their best to make it fly further. After completing its Saturn flyby mission on November 20, 1980, Voyager 1 began an expansion mission: to explore the area and boundaries of the heliopause.

Jupiter's Great Red Spot as photographed by Voyager 2.

Image credit: NASA/JPL

On another trajectory, Voyager 2's mission is to continue visiting Uranus, Neptune and some of their satellites. This is the only opportunity in human history to observe Uranus and Neptune up close.

Photo of Neptune taken by Voyager 2

Image credit: NASA/JPL

In 1990, scientists assigned a very romantic mission to Voyager 1: to take group photos of several planets in the solar system. This mission always reminds me of the Tang Dynasty poem "Looking back at Chang'an, I see piles of embroidery, a lonely city with thousands of feet of mountains, why should the Qiang flute complain about the willows, the spring breeze does not reach Yumen Pass". Or, if Voyager is likened to a traveler, after a long journey of thirteen years, a completely unexplored space appears in front of her. At this time, her mood should be "I urge you to drink another glass of wine, there will be no friends west of Yangguan"!

On February 14, 1990, Voyager 1, about 6 billion kilometers from Earth, pointed toward the sun and took 60 pictures, capturing one of the most iconic photos of the space age.

From left to right: Jupiter, Earth, Venus, Saturn, Uranus and Neptune.

Image credit: NASA/JPL

The Earth in the photo is just an inconspicuous little star spot in the sunlight, suspended in the boundless darkness. This is the famous photo that was later named "Pale Blue Dot", and it also became one of the classic scenes in the movie "The Wandering Earth 2".

Faint blue dot[2].

Image credit: NASA

3. Even if we have to say goodbye

The greatest achievement of Voyager is, of course, its flight out of the solar wind, or heliosphere, in 2012. With temperatures as high as hundreds of thousands or even millions of degrees Celsius, the outer atmosphere of the sun is much hotter than its "surface" temperature of a few thousand degrees Celsius, like fried ice cream or steam rising from a pot of boiling water. The sun continuously "blows" out charged particles, forming the solar wind, which extends to the heliosphere, like a huge bubble surrounding the sun and eight planets. Most of the matter within the heliosphere comes from the sun, while the interplanetary space outside the heliosphere is filled with background matter from the Milky Way. The solar system is not stationary; it moves around the center of the Milky Way at more than 220 kilometers per second. Following the direction of the sun's movement, Voyagers 1 and 2 successively passed through the boundary between the shock wave and the solar wind and entered interstellar space[3]. This was the first time in human history that a properly functioning spacecraft had reached interstellar space, and it was also the first time that matter and fields in this region were detected in situ.

Schematic diagram of the spatial location of Voyager 1 and Voyager 2.

Image credit: NASA/JPL-Caltech 2012 August

In January and April 2013, Voyager 1 recorded two violent encounters between solar wind particles and interstellar medium particles. After repeated modeling, NASA announced on September 12, 2013 that Voyager 1 had crossed the heliopause. Six years later, Voyager 2 became the second probe in history to cross this boundary layer. Scientists were surprised to find that the density of matter in interstellar space is higher than that in the solar wind. So far, this remains an unsolved mystery.

In my heart, I always hope that they can keep working, but as the Voyagers get older, scientists have shut down some instruments to save power. However, recently there was news that Voyager 1 could not communicate normally, but began to send some illogical garbled codes, like a dying old man, and began to speak nonsense, and the last command feedback of Voyager 2 was also 3 years ago. In more than 40 years of space travel, both probes have encountered unexpected communication failures and have achieved journeys far beyond their original destinations. Although the technical team has worked hard to carry out repairs and hopes to create miracles again, it is foreseeable that one day, they will return to silence and really become a space drifting bottle, waiting for alien life to discover it.

Will these two gold-plated records really become a bridge for interstellar communication in the future? It is still an unsolved mystery. Even though we are as small as "a speck of dust suspended in the sun", in the vast universe, this "Earth's business card" carries mankind's curiosity and eternal expectation about the unknown universe.

Note:

[1] In the 1960s, scientists observed that Jupiter, Saturn, Uranus and Neptune would form a long arc with the Earth in the late 1970s and early 1980s. Spacecraft would only need a small amount of fuel to make course corrections, and the rest of the time they could use the gravity of the planets to accelerate, so that a single spacecraft could visit the four gas giants. This geometric arrangement of planets occurs only once every 176 years.

[2] The actual image used in the film was a "rewashed" version of the photo released by NASA in 2022, which had its brightness levels and colors adjusted to enhance the area containing the Earth.

[3] There are many ways to define the boundaries of the Solar System, so the Voyagers' actions can be strictly described as entering interstellar space rather than flying out of the Solar System.

Author: Liu Yong, Ambassador of China's Space Science Popularization, Director of the Science Popularization Committee of the Chinese Society of Space Science

Reviewer: Zhou Xuzhi, Researcher, School of Earth and Space Sciences, Peking University

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.