Solar-Terrestrial Environment at the Birth of Life

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K20943
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 17:Earth and planetary science and related fields
• Research Institution: The University of Tokyo (2021-2022); Nagoya University (2020)
• Principal Investigator: Imada Shinsuke 東京大学, 大学院理学系研究科(理学部), 教授 (40547965)
• Project Period (FY): 2020-07-30 – 2023-03-31
• Keywords: 太陽 / プラズマ / 太陽風 / 太陽フレア / 太陽周期活動

Outline of Final Research Achievements

3.5 billion years ago, when life is said to have begun on Earth, according to the standard model, the sun was darker than it is today, and the Earth was in a frozen state, making it difficult for life to emerge. The reason why the ancient Sun is thought to be dark is that nuclear fusion reactions in the early Sun are thought to be inactive, and the Sun at that time was thought to be only about 75% as bright as it is today. Several solutions to this paradox have been proposed so far. So far, the influence of greenhouse gases has been mainly studied, but many unexplained phenomena have not yet been resolved. In this research project, we studied the possibility that "the ancient sun was not actually dark", which is completely different from the past study, from the standpoint of the solar-terrestrial environment and astronomy.

Free Research Field

宇宙空間物理学

Academic Significance and Societal Importance of the Research Achievements

本研究計画は「太陽系と生命はどのように生まれて来たのかの解明」に直接答えを与えうるものであり、宇宙科学分野全体に与える意義は大きい。さらに、もし初期太陽が今より数%重かった場合、太陽系の惑星形成、地球以外の惑星大気の進化等、周辺の分野に多大な影響を及ぼしうる。それぞれの分野で確立されている観測事実や理論モデルと重たい初期太陽は矛盾しうる。逆に、これまで初期太陽が現在の太陽と変わらないものを想定していたために、説明できなかった現象が説明できる可能性もあり「The Faint Young Sun Paradox」の天文学的なアプローチは周辺分野への波及効果は大きい。