Special Lecture

Earth, Water, Air, and Fire in and beyond the Solar System

Dr. Saeko S. Hayashi

Administrative Director, Project Professor

Kavli Institute for the Physics and Mathematics of the Universe, WPI

The University of Tokyo Institutes for Advanced Study

The University of Tokyo

Abstract

Have you ever wondered if another planet like Earth exists somewhere in the universe — a place with oceans, volcanoes, maybe even life?

How many planets are there in the universe?

In our Solar System, we know of eight planets. But what about in the Milky Way Galaxy, where there are about 100 billion stars? If even half of those stars (especially stars like our Sun that live a long time) have at least one planet, then there could be billions of planets in our galaxy alone!Could some of those planets be like our own Earth? As of September 2025, astronomers have confirmed about 6,000–7,500 exoplanets, and the number is growing thanks to new and powerful telescopes. Let’s take a look at what some of these “alien worlds” are like.

And what about the elements that make up us and the planets?

Most of them were formed inside stars. Scientists think that some precious metals, like gold and platinum, were created in extremely rare events: the collision of two dense stars called neutron stars. Today, we can find those same elements around us. So, let’s explore: how did the elements travel from old generations of stars, into the birth of our Solar System, and finally onto Earth — where they became part of us?

Biography

Saeko S. Hayashi was born on the snowy side of Japan and grew up under a sky full of stars. From a young age, she wondered: Why does snow fall? Why do stars shine? That curiosity led her to Tokyo, where air pollution, bright lights, and busy life often hide the night sky.

At the University of Tokyo, she studied astronomy as an undergraduate and later became the first woman in the Department’s graduate school. She did her research at the Nobeyama Radio Observatory, now famous thanks to a Detective Conan movie. She never rode the dolly like Conan did, but spent long hours high on the telescope, working to improve its performance.

Since then, she has dedicated her career to building big telescopes, no matter how challenging the project. She lived many years in Hawai‘i, then in California to help design and build components for the next generation of extremely large telescope — the one your generation will use.

Now based in Chiba, she serves as Administrative Director at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), coordinating researchers from around the world. More than half do not speak Japanese; instead, they share a universal language: numbers, formulas, diagrams — and passion for discovery.

She is a member of the Astronomical Society of Japan, the American Astronomical Society, the Royal Astronomical Society (UK), SPIE, and the International Astronomical Union.

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