Mass-produced heavenly bodies

Junji Yamamoto

Exploring Space from the Bowels of the Earth

Junji Yamamoto , Associate Professor

Hokkaido University Museum, Graduate School of Science (School of Science, Earth and Planetary Sciences)

High school : Hikone Higashi High School (Shiga Pref.)

Academic background : University of Tokyo, Graduate School, Faculty of Science

Research areas
Research keywords
earth’s interior, mantle, terrestrial materials, rocks, minerals, solar system

What are your goals?

I am attempting to create a map of the interior of the earth.

The natural phenomena and environmental problems we see around us do have a connection to movement inside the earth. Heat and gases emitted from inside the earth have dramatically transformed the environment on the earth's surface, and will probably continue to do so in the future. I believe that it is vital to understand the interior of the earth in order to predict its future. For this reason, I have taken up the challenge of drawing a map of the interior of the earth. The figure on the right is an imaginary cross-section of the earth's interior. This is just one of many models. Does it resemble the form of the interior of the earth as you have imagined it?




What kind of research are you carrying out?

Photo 1. A xenolith Found in Akita Prefecture 
Maximum width 3 cm.

Photo 2. When a xenolith was cut into thin slices
observed with a microscope, fluid of this kind
was discovered. 
Xenolith found in Oga City in Akita Prefecture. 
Width of the photo = 0.2mm.

Photo 3. Micro-raman spectroscopic analyzer.
It can analyze the pressure of fluid inside
a mineral without destroying the sample.

I am developing a device to look inside the interior of the earth. Until now, the interior of the earth has been investigated based on physical information such as the speed of seismic waves or electrical conductivity. These taught us about the material properties of the interior, but it has been difficult to discuss its chemical structure or evolution, or the types of minerals it contains or how it moves. So I hit upon the idea of using a specific type of rock to directly observe the interior of the earth. This rock is called a xenolith (Photo 1). As magma rises from deep in the earth, the rocks on the wall of its route are carried to the surface. These are xenoliths. Xenoliths are the rocks that form the interior of the earth, so we can use them to examine our planet’s interior in detail. Now why do you suppose xenoliths have not been used very much until now? The reason is that we have not been able to properly tell from how deep these xenoliths have come. Even if we discovered a xenolith with a unique chemical composition or structure, it was difficult to consider where this xenolith had existed inside the earth or to theorize about its expansion or significance. So I am attempting to develop a method of estimating the original depth of xenoliths.
The photo on the right (Photo 2) shows a fluid discovered through microscopic observation of a xenolith. It is made up mainly of carbon dioxide fluid. Carbon dioxide fluid of this kind is often seen in xenoliths. This fluid has an extremely high pressure, but why? Because it was in the interior of the earth where the pressure is high. This means that the pressure of this fluid is a record of the pressure when the xenolith was inside the earth. So if we could precisely measure the pressure of this fluid, we could determine the original depth of the xenolith.

Because we want to investigate the pressure of the fluid, we have to investigate it in situ, within the xenolith. I have developed a method of performing a non-destructive examination of the pressure of a fluid using a machine called a micro-raman spectroscopic analyzer (Photo 3). I can now precisely determine the original depth of a xenolith using this method. And I am nearing the stage where, by combining this with the constituent minerals, chemical composition, mineral texture, and other information about a xenolith, we can discuss just what kinds of rock exists at what depths.


What do you plan to do next?

Hypothetical drawing of the time when the solar system
was forming. The planets are being created 
with interstellar
matter as their material.  

Knowledge of the earth will teach us how the solar system
came into existence.

I intend to explore the process of formation of the solar system. Have you ever wanted to go into space? I aspired to become an astronaut in order to study the reasons why we have come into existence. There were no astronauts in Japan at that time. I was always thinking how I could become one, and decided to research geoscience in in order to be selected to travel into space when we begin to explore for resources out there. In the course of my studies, I gradually began to notice that the chemical composition of the earth seemed to resemble that of meteorites. That is of course due to the fact that the earth was created through the agglomeration of meteoric material, but I began to wonder if by investigating the earth in more detail, we could specify the types of meteorites that formed the material of the earth, and discover the process through which the solar system was created. This research might give us an answer to the old question of whether the earth is unique in space. This means that I will continue to explore space from the deepest bowels of the earth, clutching a map of the earth in my hand.