Revealing secrets of Earth and beyond held in magnetic fields
with Assoc. Prof. Futoshi Takahashi
Most well-known for its usefulness determining direction, Earth’s magnetic field is also critical for preventing a constant stream of harmful, charged particles from the sun known as the solar wind from stripping away our atmosphere and interfering with satellites in space. Without this barrier, life on Earth would be in danger and vital electronic systems disrupted.
“Though it may easily be taken for granted since we cannot see or feel it, Earth’s magnetic field is closely tied to our current life style,” says Futoshi Takahashi, associate professor of Kyushu University’s Faculty of Science. “Furthermore, it is not constant, so predicting changes is important for supporting our daily lives.”
Takahashi and his research group are studying and developing models of the magnetic fields of Earth, the planets, and their moons to clarify how they are generated and evolve. Information gleaned from such models will be important for forecasting changes in Earth’s magnetic field along with implications such changes may have for navigation systems and electronics, but the possibilities go much further.
Originating from deep within the planets and moons, the magnetic fields also hold a trove of information about the internal structure and history of the heavenly bodies hosting them, and Takahashi is aiming to reveal these secrets with theories and simulations that can explain experimental measurements and observations from throughout the solar system.
In the case of our home planet, the magnetic field primarily originates from the swirling of hot, liquid iron in Earth’s outer core—a roughly 2,200-km-thick layer starting about 2,900 km below the surface—through a mechanism called a dynamo. During his early work, Takahashi reported in 2005 the most accurate and precise numerical calculations at the time for simulating Earth’s dynamo.
Since then, he has been exploring other planets and moons to further generalize our understanding of such dynamos and gain new insight into our solar system. Using satellite data from two lunar orbiters, JAXA’s KAGUYA and NASA’s Lunar Prospector, Takahashi found evidence in traces of magnetism near the lunar surface that the Moon previously had a dynamo producing a magnetic field that does not align with the current orientation of the Moon’s axis of rotation.
“This points to a dramatic change in the Moon’s rotational axis occurring at some time in its history, giving us new understanding about the origin and evolution of the Moon,” explains Takahashi.
More recently, Takahashi clarified the mechanism generating the magnetic field of Mercury, which differs greatly from that of Earth. By taking into account the internal structure of the planet’s core, he was able to simulate a field consistent with measurements from the MESSENGER spacecraft. This work not only helps to better understand Mercury but also reinforces the importance of satellite data for unraveling the secrets of the planets and improving dynamo theory.
Takahashi has also played a role in the collection of such satellite data, participating in the development and calibration of the magnetometer for the KAGUYA mission studying the Moon. Because interference from other components must be avoided to precisely measure magnetism of the Moon, every part had to be thoroughly developed and tested in collaboration with JAXA, parts makers, and other researchers to be electro-magnetically compatible.
“Space missions truly rely on the collaboration of an enormous number of people with various backgrounds, which is an experience that I will never forget,” remembers Takahashi. “In many ways, through both chance meetings and fortunate timing, that project helped to put me on the trajectory to where I am today.”
As he continues on this course, Takahashi and his group hope to further explore our solar system through magnetic fields while also getting a better understanding of just how unique and special our own planet might be.