Kei Hirose

The 2024 Robert Wilhelm Bunsen Medal is awarded to Kei Hirose for outstanding research, combining innovative experimental and analytical techniques, on the behaviour and evolution of the Earth’s deep interior.

Kei Hirose is a highly productive scientist, and a world-leading original thinker, combining innovative experimental and analytical techniques to investigate the behaviour and evolution of the deep interior of the Earth. His work has had a profound impact on our understanding of the nature of observed seismic discontinuities in the mantle, and of the composition and behaviour of the Earth’s core: there is no important topic in deep Earth geophysics that he hasn’t advanced through experimental work combined with profound insights for its implications.

Perhaps his best-known achievement is the discovery of the post-perovskite phase that controls the properties of the lowermost mantle, confirming pre-existing seismic evidence and inspiring a flood of further investigations by seismologists and mineral physicists. This breakthrough was enabled by his development of experimental apparatus that can generate ultra high P-T conditions exceeding those found in the centre of the Earth. The nano-scale experimental volumes of this novel multi-anvil and laser-heated diamond anvil cell technology also required the development of in situ analytical approaches, such as synchrotron X-ray diffraction and spectroscopy.

Other important work with fundamental implications for planetary behaviour is his work on light elements dissolved in the core, providing the framework for understanding seismic observations that show the density of the outer core is less than that of iron. He has showed that the physical properties of the core are compatible with significant amounts of dissolved hydrogen, and that the presence of dissolved silica in the core may contribute to the powering of the Earth’s geodynamo. He has contributed to the understanding of the fate of subducted oceanic lithosphere and crust in the deep mantle, demonstrating that oceanic crust becomes denser than the surrounding mantle near the Earth’s core, initiating a major effort in the geodynamics community to unravel the implications of this for the large low shear velocity provinces at the base of the mantle.

Hirose is also an outstanding leader and contributor to the Earth Sciences community. He established the world-leading Earth-Life Science Institute, the first international research institute in Japan focused on Earth Sciences. He has an excellent record of supervising and nurturing early career scientists: a large proportion of his former graduate students and postdoctoral associates have moved on to independent positions. He served as an editor of ‘Physics of the Earth’ and ‘Planetary Interiors’ for more than a decade. With all these outstanding contributions, Kei Hirose is highly deserving of the Robert Wilhelm Bunsen Medal.