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Emergence of two types of terrestrial planet on solidification of magma ocean

机译：两种类型的地球行星在岩浆海洋凝固中的出现

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摘要

Understanding the origins of the diversity in terrestrial planets is a fundamental goal in Earth and planetary sciences. In the Solar System, Venus has a similar size and bulk composition to those of Earth, but it lacks water. Because a richer variety of exoplanets is expected to be discovered, prediction of their atmospheres and surface environments requires a general framework for planetary evolution. Here we show that terrestrial planets can be divided into two distinct types on the basis of their evolutionary history during solidification from the initially hot molten state expected from the standard formation model. Even if, apart from their orbits, they were identical just after formation, the solidified planets can have different characteristics. A type I planet, which is formed beyond a certain critical distance from the host star, solidifies within several million years. If the planet acquires water during formation, most of this water is retained and forms the earliest oceans. In contrast, on a type II planet, which is formed inside the critical distance, a magma ocean can be sustained for longer, even with a larger initial amount of water. Its duration could be as long as 100 million years if the planet is formed together with a mass of water comparable to the total inventory of the modern Earth. Hydrodynamic escape desiccates type II planets during the slow solidification process. Although Earth is categorized as type I, it is not clear which type Venus is because its orbital distance is close to the critical distance. However, because the dryness of the surface and mantle predicted for type II planets is consistent with the characteristics of Venus, it may be representative of type II planets. Also, future observations may have a chance to detect not only terrestrial exoplanets covered with water ocean but also those covered with magma ocean around a young star.
机译：了解地球行星多样性的起源是地球和行星科学的基本目标。在太阳系中，金星的​​大小和体积组成与地球相似，但缺少水。由于预计将发现更多种类的系外行星，因此要预测它们的大气和地表环境，需要一个行星演化的通用框架。在这里，我们表明，根据标准地层模型预期的初始热熔融态，根据凝固过程中的演化历史，可以将它们划分为两种不同的类型。即使除了形成轨道之后它们的轨道相同之外，凝固的行星也可以具有不同的特性。距主恒星超过一定临界距离形成的I型行星在数百万年内凝固。如果行星在形成过程中获取水，则其中的大部分水将被保留并形成最早的海洋。相反，在临界距离内形成的II型行星上，即使初始水量较大，岩浆海洋也可以维持更长的时间。如果地球与大量水形成可比的现代地球总存量，则其持续时间可能长达一亿年。在缓慢的凝固过程中，流体动力逃逸使II型行星干燥。尽管地球归类为I型，但尚不清楚金星属于哪种类型，因为它的轨道距离接近临界距离。但是，由于为II型行星预测的地表和地幔干燥度与金星的特征一致，因此它可能是II型行星的代表。而且，未来的观察可能不仅有机会发现覆盖有水洋的陆地系外行星，而且有可能检测到一颗年轻恒星周围的岩浆洋所覆盖的行星系外行星。

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  • 来源
    《Nature》 |2013年第7451期|607-610|共4页
  • 作者

    Keiko Hamano; Yutaka Abe; Hidenori Genda;

  • 作者单位

    Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;

    Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;

    Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan,Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama,Meguro-ku, Tokyo 152-8551, Japan;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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