2026-05-07 カリフォルニア工科大学（Caltech）
This diagram illustrates various stages in the process of core formation for Ganymede. The new study suggests that Ganymede’s dynamo began as the moon’s core was still “cold,” in its earliest days of formation.Credit: K. Trinh
＜関連情報＞
- https://www.caltech.edu/about/news/ganymede-might-still-be-forming-its-metal-core-today
- https://www.science.org/doi/10.1126/sciadv.aed8021
長期にわたる核形成によってガニメデのダイナモを駆動する Powering Ganymede’s dynamo with protracted core formation
Kevin T. Trinh, Flavio Petricca, Douglas J. Hemingway, and Steven D. Vance
Science Advances Published:6 May 2026
DOI:https://doi.org/10.1126/sciadv.aed8021
Abstract
Ganymede is the only known moon with an active dynamo today. Previous studies interpret Ganymede’s dynamo as arising from convection in a metal core that formed billions of years ago. However, Ganymede likely accreted too cold to form with a metal core, which confounds interpretations of Ganymede’s magnetic field as a constraint on the moon’s broader history. Here, we reevaluate the thermal evolution of Ganymede’s rock-metal interior from a cold start. Our models show that Ganymede’s observed dynamo is consistent with ongoing core formation, a process not yet observed elsewhere. If Ganymede has an Fe-FeS core with a sub-eutectic composition, then gradual mantle warming may expel dense Fe melt onto the growing protocore and stir liquid metal, sustaining a dynamo for billions of years.
