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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/5990

    Title: 小行星對於地球原始海水的貢獻;The Contribution of Asteroids to the Primordial Terrestrial Ocean
    Authors: 游大立;Dah-Lih You
    Contributors: 天文研究所
    Keywords: 地球海洋;起源;小行星;軌道演化;asteroid;orbital evolution;terrestrial ocean;origin
    Date: 2003-06-10
    Issue Date: 2009-09-22 10:11:32 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 地球生命的起源一般相信是源自地球的海洋,因此海洋的起源成為生命起源的根本問題。太陽系內的彗星、小行星及地球吸積過程中所獲得的水,均可能是地球海水的來源。其中源自小行星帶共振區的小行星,可能是重要的來源物質。 使用SWIFT (Levison & Duncan 1994) 的RMVS 3 (Regularied Mixed Variable Sympletic 3) 程式直接積分 (direct integration) 計算大約一萬顆分佈於小行星帶中可能的近地小行星來源中介區 (intermediate source),積分計算100 Myr (106年)。經由統計各來源區小行星對於類地行星 (僅計算金星、地球及火星) 的撞擊機率,估計小行星帶物質在太陽系行星系統形成之初,小行星帶物質對於地球及類地行星原始海洋可能的貢獻。 計算結果顯示源自內小行星帶共振區的原始小行星在地球形成後,大約可以提供一倍至數十倍現今海水質量的水至地球。原始太陽星雲的初條件的設定對於小行星帶物質的貢獻影響非常敏感。 綜合D/H值證據,研究結果傾向支持小行星對於地球原始海洋的貢獻較彗星來得重要。而原始地球在吸積形成過程中,也可能未完全將水等揮發物質完全盡空。因此原始地球對於地球海水的貢獻也不可忽略。 Direct integration method using the SWIFT RMVS3 (Regularized Mixed Variable Sympletic 3) code has been used to investigate the long-term (~ 100 Myr) orbital evolution of about 10 thousand test particles originally distributed in the asteroid belt. This is to provide statistical estimates of the collisional probabilities against surface impacts with Mars, Earth and Venus by strary bodies ejected from such intermediate source region of the Near-Earth asteroids. The major goal is to investigate the potential contributions to the primordial oceans of the terrestrial planets from the asteroidal objects. Our calculations suggest that Earth could in principle gained between one to a few tens of the present oceanic water from asteroidal impact. But the exact value depends sensitively on the assumption of the initial mass distribution in the solar nebula. When compared with the isotope ratios of D/H of the Standard Mean Oceanic Water (SMOW), the cometary water and primitive meteorites, it is concluded that asteroids should be a more important source of oceanic water than comets. But water contained in the Earth’s interior could also make significant contribution.
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