地球科学：地球の中心に何があるのか

New insights into the potential presence of an innermost inner core of Earth, suggesting it may be a ball of iron with a radius of approximately 650 km within the inner core, are reported in a study published in Nature Communications. The findings may improve our understanding of Earth’s formation and evolution.

Probing the Earth’s center is critical for understanding planetary formation and evolution. The presence and size of such an innermost inner core has long been hypothesized and has been subject to debate. However, probing the Earth’s innermost core has been challenging due to a lack of probes sensitive enough to sample the Earth’s deep interior.

Thanh-Son Phạm and Hrvoje Tkalčić collated data from existing probes to measure the different arrival times of seismic waves of energy created by earthquakes as they travelled through the Earth. They observed for the first time the waves reverberating along the entire Earth’s diameter up to five times. The travel times of the waves suggest the presence of a distinct internal shell, with a radius of approximately 650 km, which is separate from the outer layer of the inner core. This internal interface may reflect a past change in the inner core growth, the authors suggest.

Future research efforts should focus on the characterization of the transition between the innermost inner core and the inner core’s outer shell, to better understand Earth’s deep interior and its generation history, the authors suggest.