Professor Sugimoto answers with the calm perspective of a scientist.

"Venus is a failed Earth. There is a theory that it once had oceans, and its size is almost the same as Earth's. Yet, one became a planet that nurtures life, while the other became a harsh planet where surface temperatures reach 460 degrees Celsius. I want to clarify the 'boundary' where this difference originated."

Venus, the subject of Professor Sugimoto's research, is called a "sister planet," but its true nature bears no resemblance to Earth.

More than 95% of the atmosphere is carbon dioxide. Because thick clouds of sulfuric acid completely cover the entire planet, it is difficult to observe the atmosphere or the surface from the outside. While the hurdles for research seem high, Professor Sugimoto says he was actually drawn to that challenge.

"In the first place, 'wanting to know what is unknown' was the reason I chose the path of a researcher. Mars had already been explored quite a bit, but I thought I could make a breakthrough with Venus, which was shrouded in a veil of mystery."

The most significant feature of Venus is "super-rotation," where the atmosphere circulates at a speed far exceeding the planet's rotation speed. While Venus has a very slow rotation period of 243 days, the upper atmosphere moves at 100 meters per second (a period of about 4 days). Why does the atmosphere rotate 60 times faster than the ground moves? This atmospheric mystery was one of the greatest mysteries in planetary science.

To solve this difficult problem, Professor Sugimoto developed a world-first "weapon." It is a unique system that fuses observation data from the Japanese Venus probe "Akatsuki" with an atmospheric circulation model utilizing the Earth Simulator.

Normally, simulations tend to be completed solely through theoretical calculations on a computer, but the atmosphere of Venus is so complex that theory alone cannot reproduce actual movements. Therefore, Professor Sugimoto applied a method called "ensemble data assimilation" to Venus for the first time, in which actual observation data captured by the Akatsuki probe is fed in real-time during simulation calculations to correct them toward "reality." Through this, he succeeded in reproducing the Venusian atmosphere three-dimensionally.

Furthermore, using this system, Professor Sugimoto achieved a major discovery. The analysis by Professor Sugimoto and his colleagues clarified the conversion efficiency when "thermal tides"—giant waves caused by atmosphere heated by sunlight—are converted into energy that accelerates the atmosphere. These "thermal tides" are believed to be related to the energy that accelerates and maintains super-rotation.

Professor Sugimoto's gaze does not stop at simply looking at Venus as it is now. Using the Earth Simulator, he is conducting a grand experiment of running "hundreds of Venuses" inside a computer.

"I try creating various patterns of planets in the simulation by slightly changing the distance from the sun or swapping atmospheric components. Then, I can see the moment when the planet's environment changes drastically at a certain condition. This is the scientific boundary line: up to this point it can be maintained like Earth, but beyond this point it runs away like Venus."

Professor Sugimoto has a unique philosophy of "not treating Earth as special." He says that by viewing Earth and Venus as samples among the many planets existing in the universe, their objective forms first become visible.

"No one actually knows yet why Earth became the way it is now, what will happen in the future, or if other similar planets exist. That is why I use simulations to explore where the 'habitable' environment that allows life to persist is determined. Defining that boundary in the language of physics leads to knowing the current position of the planet Earth."

He is also leading meteorology on a solar system scale, advancing unique applied research in atmospheric data assimilation for Earth and Mars.

"I discovered the energy conversion method itself on Venus, but it can also be used for Earth. There is a phenomenon called blocking, where high and low-pressure vortices stay in a certain area for many days; I believe that using this method, it is possible to predict the reasons for blocking and when it will resolve."

The starting point for Professor Sugimoto was when he learned about meteorologist Edward Lorenz's "Chaos Theory" while enrolled in the Faculty of Science at Kyoto University.

In the past, physics had progressed in research that scrutinized small things, such as quantum mechanics, but no matter how much micro-elements were scrutinized, "chaos" would arise in a world where they gathered in large quantities, making it difficult to accurately predict the future.

"I felt that I couldn't reach the roots of physics unless I confronted chaos."

A butterfly flapping its wings in Brazil causes a tornado in Texas, USA. Many people have likely heard the term "Butterfly Effect," which suggests that small changes people don't even notice can significantly change future weather and other events. It was in 1972 that Lorenz gave his famous lecture using this "butterfly flapping" as an example. As a meteorologist himself, he was facing the problem that "weather forecasts don't come true because there is chaos."

"Any field where I could study chaos was fine." With that thought, Professor Sugimoto began his path in "meteorology." Then, at Keio University, where he took a teaching position at age 30, he became fascinated by Venus research.

Professor Sugimoto's team is the only one in the world that has succeeded in "data assimilation" fusing Venusian observation data with numerical simulations. Large-scale calculations, such as running "hundreds of Venuses" using the Earth Simulator, support this achievement.

"By creating a dataset that includes information that could not be obtained through horizontal image observation alone, we can reproduce vertical wind movements and temperature distributions that were previously invisible. This means a database for investigating various phenomena on Venus has been completed."

It is also expected to be utilized in Venus exploration missions conducted by NASA (National Aeronautics and Space Administration) and ESA (European Space Agency).

The reason weather forecasts do not have a 100% probability is due to chaos. Regarding the differences in how the error between such predictions and reality spreads, the Venus research by Professor Sugimoto and his colleagues is beginning to bear fruit.

"Predictability on Earth is one or two weeks, after which weather forecasting becomes impossible, but on Venus, it might be possible to make a one-month forecast. I am happy at the moment I understand the differences between Earth and Venus; that is the real pleasure of comparing and investigating planetary atmospheres."

Elucidating the extreme meteorological mechanisms of Venus directly leads to improving the accuracy of simulations that predict the future global environment. If progress is made in elucidating the atmospheres of Venus and Earth, it might become possible to change them artificially. Professor Sugimoto says that terraforming Venus (making the planet Earth-like) is not impossible in the future.

However, Professor Sugimoto is skeptical about the implementation of terraforming or "geoengineering" (climate engineering) to artificially alter Earth's environment.

"If we scatter volcanic ash in the stratosphere to reduce sunlight, Earth's temperature will drop, but how long should we keep adding ash? Furthermore, plant growth might slow down due to the ash, and it might cause global cooling."

Maintaining a "sense of awe toward nature" is a point of pride for Professor Sugimoto as a scientist.

"I want to protect the situation where there are many living things, and I don't want to destroy an interesting field. That's why I don't want to alter Earth."

Professor Sugimoto's current primary place of education is at the Hiyoshi Campus. It has been nearly 20 years since he began teaching physics to undergraduate students in the humanities. At Keio University, in order to acquire the ability to think logically based on evidence and to describe the results, he conveys the process of science through experiments for students in the four humanities faculties (Faculty of Letters, Faculty of Economics, Faculty of Law, and Faculty of Business and Commerce).

In the coming era, there are mountains of issues that cannot be solved by a single country alone, such as climate change and energy problems.

"Science can also cause environmental destruction if the use of knowledge is mistaken. Knowing the complexity of natural phenomena and understanding the limits of science and technology is essential. I hope to see the growth of leaders who can create a society that can correctly control technology, as well as the ethics of scientists."

The gaze of the scientist looking at the harsh sister planet in the distant universe is directed straight toward those who will carry the future of Earth.

Composition: Toru Tamakawa, Editor-in-Chief of Asahi Shimbun GLOBE+

Interview/Text: Nasuka Yamamoto

Photography: Hidehiro Yamada