Research press release


Nature Geoscience

Life on Earth thanks to solar superflares?



太陽に似た若い星の上の嵐で、大量の高エネルギー粒子が爆発的に放出される様子を望遠鏡で観測した結果に基づいて、Vladimir Airapetianたちは、同じように嵐を起こしていた若い太陽がしばしば高エネルギー粒子を爆発的に地球に向けて放出し、このいわゆるスーパーフレアが初期地球大気の化学的性質変化の引き金となったという仮説を述べている。彼らは、そのような荷電粒子の雲は地球に頻繁に(おそらく一日に一回以上)衝突していたと見積もっている。スーパーフレアと地球との間の相互作用の数値シミュレーションは、スーパーフレアが極間に大きな隙間を形成することで地球磁場に擾乱を引き起こし、それによって高エネルギー粒子が大気に侵入する経路を作ったことを示唆している。


関連するNews & Views記事で、Ramses Ramirezは、提案した過程は初期火星の環境にも影響を与えた可能性があり、「極めて年代の若い、太陽に似た恒星の周りを回っている太陽系外惑星の気候と生命体の可能性に対しても意味を持つ可能性がある」と述べている。

An active young Sun could have helped to provide the early Earth with the ingredients and climate required for life, according to a study published online this week in Nature Geoscience.

Nitrogen (N) is an essential component for the building blocks of life on Earth, but it is likely that it was originally only available in the young Earth’s atmosphere in the form of molecular nitrogen (N2) - which is not very chemically reactive. An energetic process would have been required to break apart the nitrogen molecules in the atmosphere, so that nitrogen could then recombine in more biologically useful forms.

Based on telescope observations of stellar storms on Sun-like young stars, in which massive bursts of energetic particles are ejected, Vladimir Airapetian and colleagues hypothesize that a similarly stormy young Sun could have unleashed frequent bursts of energetic particles towards the Earth, and that these so-called superflares triggered changes to the early Earth’s atmospheric chemistry. They estimate that such clouds of charged particles could have hit the Earth frequently - perhaps more than once per day. Numerical simulations of the interactions between the superflares and the Earth suggest that the superflares distort the Earth’s magnetic field by creating large gaps around the poles, which provide pathways for the energetic particles to penetrate the atmosphere.

The authors then find that the energetic solar particles interact with components of the Earth’s atmosphere, including molecular nitrogen, to generate nitrous oxide (N2O) and hydrogen cyanide (HCN). They suggest that the HCN could have provided a nitrogen source for building biological molecules such as amino acids, and that the N2O - a potent greenhouse gas - could have helped warm the Earth’s surface to a temperature that could support liquid water and the beginnings of early life. This occurred at a time when the Sun, despite its storminess, was 30% dimmer than it is today.

In an accompanying News & Views article, Ramses Ramirez writes that the proposed process could have also influenced the environment on early Mars and, “may have implications for the climates and potential biology of terrestrial exoplanets orbiting very young Sun-like stars.”

doi: 10.1038/ngeo2719


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