When his grandfather saw Sakon get bored of watching the baseball game between the Hanshin Tigers and the Yomiuri Giants, he took him by the hand and led him out onto the small rooftop of his house under the night sky full of stars. This is a vivid memory of the beginning of Sakon's love affair with stars when he was three years old.
Young boy Sakon's interest in space grew stronger and stronger. At long last, he managed to get his hands on an astronomical telescope, something he had wanted since junior high school. It was 1994 when Comet Shoemaker-Levy 9 collided with Jupiter.
“I wondered if intelligent life like humans existed only on Earth, or if it also existed somewhere else among the twinkling stars in the night sky. I have been thinking about such things since I was a child. I believe that astronomy and philosophy are two sides of the same coin. Why do human beings have consciousness? Why am I here? Why are we here on Earth? What is our mission? These questions have always been curious to me. Philosophy pursues these questions internally, but I thought the methods of natural science suited me better. That is why I decided to become an astronomer.”
His philosophical interest continues to this day.
Compared to the 13.8 billion years of the history of the universe, the history of humankind is only 2 million years. It is just a blink of an eye. Will the day ever come when humanity can confirm the existence of life on other planets and to find its “neighbors” in the universe?
“Contrary to communicating with UFOs and aliens in science fiction, it is challenging to make contact with intelligent life in the outside world under the universal laws of physics. That said, I think it is possible that “neighbors” in the universe are trying to find each other. However, if the existence of intelligent life on another nearby planet overlapped with the very short a few million years of human existence, that would be tantamount to a miracle. Therefore, we should be more aware of the rarity and preciousness of our existence.”
What it means to be human on cosmic timescales that feel like eternity is the question Sakon is passionate about. And that passion drives his research to discover the origin of life in the universe.
Mysterious infrared rays
In astronomy, making new instruments makes previously invisible phenomena visible, leading to discoveries. Thus, instrument building is a vital aspect of research, and Sakon has been interested in this field since he was an undergraduate student. Upon entering graduate school, he joined the Japanese infrared astronomy satellite project called AKARI and became a member of the team in charge of the near and mid-infrared instrument. He worked for the development of the software that converted the images into spectral data.
“The launch was in 2006 when I was a first-year PhD student. I went all the way to Uchinoura Space Center in Kagoshima to watch the launch. My work on the project was to study the characteristics of artifacts (artificial noise) in the data sent from AKARI and to identify their origin. It was fun. I enjoyed discovering unexpected artifacts and identifying them as I investigated their characteristics. I often stayed overnight at the university to not waste even a second.”
It was around this time that Sakon first encountered unidentified infrared emission bands, a research theme that later lead to an experiment he performed successfully for the first time in the world.
Unidentified infrared bands were discovered in 1973. As scientists observed the infrared radiation coming from space, they found “mysterious” infrared radiation, wavelengths whose origin they could not identify.
“At the time, we knew there were unidentified infrared bands everywhere in the universe but had little idea what kind of material produced them. The material was suspected to be an organic substance, possibly a PAH (polycyclic aromatic hydrocarbon = carbon-based particulate matter), but no one was able to confirm the hypothesis. My former supervisor, Takashi Onaka (Professor Emeritus of Astronomy at the University of Tokyo), and his colleagues were involved in the Japanese Infrared Telescope in Space (IRTS) program using an infrared observation satellite with a fifteen-centimeter aperture launched in 1995. I wrote my master's thesis using data from the IRTS, demonstrating that the intensity of the unidentified infrared bands relative to thermal emission from other dust grains coming from inside and outside of the Milky Way galaxy differs. At the time, some papers claimed the it was almost constant. This disagreement taught me the joys of discussion/debate. By the way, the IRTS was recovered using the robotic arm of a space shuttle and brought back to Earth by astronaut Koichi Wakata. It is now on display at the National Museum of Nature and Science in Ueno. I think it is uncommon that a telescope is recovered from space and brought back to Earth.”
What is the significance of revealing what produces the unidentified infrared bands? Sakon says it is very relevant to understanding the origin of life in the solar system.
Based on observations of the properties of light arriving from space, there are more than 200 types of molecules in interstellar space. About 70 of these are said to be complex organic molecules composed of six or more atoms, including carbon atoms. If new organic molecules that contain nitrogen, an atom that plays an integral role in the birth of life, could be identified, that could imply that the explosions of distant novae and supernovae are related to the birth of life in our solar system. Moreover, nitrogen-containing organic matter may be the clue to solving the mystery of the unidentified infrared band.
Reproducing interstellar space in an experimental machine
Stars are in a recurrent cycle of death and rebirth. Gas and dust in molecular clouds clump together, eventually growing into stars. As the stars evolve, they ultimately explode as novae or supernovae, dispersing their matter into the universe. The dispersed matter turns into molecular clouds that become stars in a next generation, and so on.
“Hydrogen, carbon monoxide, carbon dioxide, and other molecules in the molecular cloud gradually assemble into more complex molecules over time. Once the star is formed in the molecular cloud and starts to give off ultraviolet photons that stimulate chemical reactions, even larger organic matter can be formed. A mainstream view is that the organic matter created in this way in the molecular cloud from which the solar system originated may have been the origin of life on Earth.”
This is a so-called "bottom-up" process, in which organic matter is formed by taking incremental steps from the bottom, small molecules, to the top, complex molecules, while the solar system is forming. However, as mentioned earlier, some scientists believe that organic matter essential for life was already present from the beginning, in the dust that came from the explosions of other novae and supernovae. Sakon is one of them.
“If there were already compounds such as amines (organic compounds similar to ammonia) in the dust, then a "top-down" process would make more sense for the formation of complex organic materials. In fact, this may be a very efficient way to create life. Currently, it is a minor hypothesis, but that is the perspective from which I am conducting my research.”
So, how can the hypothesis be tested?
“Even before I was born, a project led by Dr. Akira Sakata and Dr. Setsuko Wada of the University of Electro-Communications was underway to produce cosmic dust in the laboratory and study its infrared characteristics to find out what is behind the unidentified infrared bands. Unfortunately, Dr. Sakata passed away in 1995. However, since 2007, the University of Tokyo has been handling the experimental apparatus Dr. Sakata had built and used since the 1970s. And so, the research continued. Even after her retirement, Dr. Setsuko Wada frequently came to the University of Tokyo to teach us how to use the equipment and conduct experiments. Thank to her, research continues to this day.”
Sakon and his colleagues, who inherited this valuable experimental apparatus, have continued to pursue their dream of discovering the identity of the "mysterious infrared radiation" just as their predecessors did. In 2021, Sakon and his colleagues were finally able to take a step forward to tacking the challenge.
Identity of unidentified infrared bands
Sakon's experiment using an interstellar dust synthesizer goes like this. Nitrogen gas and hydrocarbon solids are placed in the quartz tube and heated by microwaves to generate plasma gas. The gas is then quenched and condensed to synthesize organic matter.
“This reproduces the process by which matter forms when a star dies and spews stellar wind into space. We think we have reproduced specially well the process of dust formation around a star through the condensation of matter from the plasma state. Whether it is a nova or a supernova, the explosion releases massive amounts of energy and the elements scatter in the circumstellar space. As they cool down, they become molecules or condense into dust in one go. We were able to reproduce these processes qualitatively with the instrument. Conducting experiments with graduate student Izumi Endo and many others, we successfully introduced nitrogen into the condensing dust and analyzed the material.”
Sakon and the colleagues named the resulting material “quenched nitrogen-containing carbonaceous composite” (QNCC). The infrared emission coming from the QNCC is consistent with the infrared radiation of organic dust produced by novae, i.e., the unidentified infrared bands. Moreover, X-ray spectral analysis and other measurements confirmed that QNCC contains nitrogen in the form of amines.
“We were able to create organic dust containing amines and even condense it from plasma gas for the first time. The results corroborate the hypothesis that the substance giving rise to the unidentified infrared bands is organic dust containing amines.”
The finding also supports the proposition that organic matter was dispersed in the interstellar dust in the molecular clouds of the early solar system and became one of the origins of organic matter in the solar system and possibly of life on Earth.
However, this is not the end of the research about unidentified infrared bands. According to Sakon, even 50 years after their discovery, unknown things still outnumber the known about unidentified infrared bands. He says his current goal is to clarify the origins of this vague phenomenon.
“I want to systematically reproduce in the laboratory what kind of materials produce what kind of infrared bands in what kind of environments. It would result in an interesting yardstick for astronomy. From the observation of unidentified infrared bands, we could infer the physical environment that they come from. I would like to work on creating such a “yardstick.” It will, in turn, help us identify organic matter in the universe and how it connects to life on Earth. Since unidentified infrared bands are ubiquitous in the universe, it could also help with the question whether intelligent life exists outside of our planet.”
Taking time to think slow
Sakon does not doubt that intelligent life exists in other star systems. What is happening on Earth is not particularly unique in the universe. Water boils at 100 degrees Celsius under one atmospheric pressure on any other planet. In other words, life emerges naturally when certain physical conditions are satisfied.
“Our galaxy contains hundreds of billions of stars. There are hundreds of billions or trillions of galaxies in the universe. With that many galaxies, I think the emergence of life is probably a universal phenomenon. However, when we think about humanity, there are too many things that are unfortunate about the current state of the world. It would be terrible if it turned out that the intelligent life form that has built such an advanced civilization was so aggressive that it caused its own downfall. If we are truly intelligent beings, we should be able to make contact with intelligent life on other planets without threatening our survival. I hope I can contribute to that in some small way.”
When asked for advice for young people, Sakon replies as follows.
“I think taking time to think slow is crucial. Acquiring academic skills is important, too. However, it is you who will use those skills, so I think it is paramount to take time to prepare your mind and organize your thoughts. For example, by thinking about why you are alive, what the purpose of human existence is, and so on, you should be able to find the field you want to pursue. Spending time thinking slow about mysterious things that have no answers is intriguing. Or at least, I find it intriguing.”
Sakon, who likes to play the piano, loves classical music. He often listens to the music of Gustav Mahler, a composer on whom the German writer Thomas Mann based his main character, Aschenbach, in “Death in Venice.”
“By incorporating Goethe's poetry into his works, Mahler artistically expresses his own philosophy in his symphonies. I love them because they show how he perceived things and his way of life at the age he composed each one. They are great for getting lost in contemplation.”
Sakon’s favorite is Symphony No. 2, “Resurrection,” an hour-and-twenty-minute-long piece in five movements. Sakon closes his eyes as he immerses himself in the swell of the sound of the orchestra. Under his closed eyelids, is he seeing the twinkling starry night sky as he did when he was three years old?
※Year of interview:2023
Interview/Text: OTA Minoru
Photography: KAIZUKA Junichi