Research Abstract


The Charon-forming giant impact as a source of Pluto’s dark equatorial regions

2017年1月30日 Nature Astronomy 1 : 31 doi: 10.1038/s41550-016-0031 (2017)


Yasuhito Sekine, Hidenori Genda, Shunichi Kamata & Taro Funatsu

Corresponding Author

関根 康人
東京大学 大学院理学系研究科 地球惑星科学専攻

Pluto exhibits complex regional diversity in its surface materials. One of the most striking features is the dark reddish material, possibly organic matter, along Pluto’s equator coexisting with the H2O-rich crust. Little is known, however, about the surface process responsible for the dark equatorial regions. Here, we propose that Pluto’s dark regions were formed through reactions in elongated pools of liquid water near the equator, generated by the giant impact that formed Charon. Our laboratory experiments show that dark reddish organic matter, comparable to Pluto’s dark materials, is produced through polymerization of simple organic compounds that would have been present in proto-Pluto (for example, formaldehyde) by prolonged heating at temperatures ≥50 °C. Through hydrodynamic impact simulations, we demonstrate that an impactor, one-third the mass of Pluto, colliding with proto-Pluto—with an interior potential temperature of 150–200 K—could have generated both a Charon-sized satellite and high-temperature regions around Pluto’s equator. We also propose that high-velocity giant impacts result in global or hemispherical darkening and reddening, suggesting that the colour variety of large Kuiper belt objects could have been caused by frequent, stochastic giant impacts in a massive outer protoplanetary disk in the early Solar System.