新東京大学大学院領域創成科学研究科
A four-billion-year-old catastrophe: the origin of Titan's nitrogen atmosphere

imageTitan, Saturn's largest satellite, is the only body in the solar system other than Earth with a thick nitrogen atmosphere and liquid (methane) lakes on its surface. However, it remains a mystery how and when Titan's Earth-like surface environment was formed. In this study, numerical simulations of cometary impacts and hypervelocity impact experiments using a high-energy laser gun showed that Titan's nitrogen atmosphere was formed through collisions with comets four billion years ago during the late heavy bombardment, a period of collisions involving a vast number of huge asteroids and comets throughout the entire solar system. The results of the present study also showed that not just on Titan, many current features found on the surface of icy bodies in the solar system may have been formed during the heavy bombardment event. This study proposes a new mechanism for atmosphere formation, which contributes to building a general framework for atmospheric origin and evolution on planets and satellites. It may also assist in predicting the surface and atmospheric environments, and in discussion of the viability of life, on earth-like planets beyond our solar system.
Figure: Images of Titan taken by the Cassini spacecraft (Courtesy: NASA)

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Yasuhito Sekine, Hidenori Genda, Seiji Sugita, Toshihiko Kadono, Takafumi Matsui,
"Replacement and late formation of atmospheric N2 on undifferentiated Titan by impacts."
Nature Geoscience Online Edition: Saturday, May 09, 2011 (Japan time)
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