| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000)
Fiscal Year 2015: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000)
Fiscal Year 2014: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2013: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
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| Outline of Final Research Achievements |
Hexagonal close-packed iron (hcp-Fe) is a main component of Earth's inner core. The difference in density between hcp-Fe and the inner core in the Preliminary Reference Earth Model (PREM) shows a density deficit, which implies an existence of light elements in the core. Sound velocities then provide an important constraint on the amount and kind of light elements in the core.
This study shows the compressional sound velocity (Vp) of hcp-Fe up to 163 GPa and 3000 K using inelastic x-ray scattering from a laser-heated sample in a diamond anvil cell. The result indicates that Earth's inner core has a 4 to 5% smaller density and a 4 to 10% smaller Vp than hcp-Fe. This demonstrates that components other than Fe in Earth’s core are required to explain Earth's core density and velocity deficits compared to hcp-Fe. Hydrogen is a good candidate; thus, Earth's core may be a hidden hydrogen reservoir. In addition, silicon and sulfur are also possible candidates.
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