美國的一項(xiàng)新研究認(rèn)為,，月球上的大部分水來自彗星,。在月球形成初期,，彗星曾撞擊月球表面并為其“送水”,。
過去,，人們一直認(rèn)為月球是一個(gè)干燥無水的星球。直到2009年10月,，美國航天局的“半人馬座”火箭,、月球坑觀測和傳感衛(wèi)星相繼撞擊月球南極附近的凱布斯坑后，才得出月球表面存在水的結(jié)論,。
研究人員認(rèn)為,，月球水的來源不外乎3種情形：一是來自月球構(gòu)造中類似地幔的部分，二是“太陽風(fēng)”的作用,，三是曾經(jīng)撞擊月球的彗星,。
為了確認(rèn)月球水的來源,，美國康涅狄格州衛(wèi)斯理大學(xué)教授詹姆斯·格林伍德領(lǐng)導(dǎo)的研究小組對阿波羅飛船帶回的月球表面巖石標(biāo)本進(jìn)行了分析。該小組在新一期英國學(xué)術(shù)刊物《自然地學(xué)》上報(bào)告說,，研究者重點(diǎn)測量了標(biāo)本中一類名為磷灰石的礦物所含的氫同位素組成比例,。結(jié)果發(fā)現(xiàn)，其組成比例與3個(gè)已知彗星中的氫同位素組成比例接近,，它們分別是海爾－波普彗星,、百武彗星和哈雷彗星。研究人員由此認(rèn)為,，彗星是月球上水的主要來源之一,。
彗星質(zhì)量較小，通常沿很扁的橢圓形軌道圍繞太陽運(yùn)行,。據(jù)推測,，它們是由太陽系外圍行星形成后的剩余物質(zhì)組成，包括冰凍的氣體,、冰塊,、塵埃等。
根據(jù)大碰撞假說,，大約45億年前,，地球被一顆像火星大小的天體撞擊，撞擊拋射出的碎片逐漸聚集形成了現(xiàn)在的月球,。格林伍德的研究小組認(rèn)為,，月球形成之后，彗星曾撞擊月球并為其“送水”,。根據(jù)此前的一些假說,，彗星在撞擊地球時(shí)也曾給地球帶來水和其他一些重要化合物，為地球生命起源創(chuàng)造了重要條件,。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature Geoscience doi:10.1038/ngeo1050
Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon
James P. Greenwood,Shoichi Itoh,Naoya Sakamoto,Paul Warren,Lawrence Taylor& Hisayoshi Yurimoto
Water plays a critical role in the evolution of planetary bodies1, and determination of the amount and sources of lunar water has profound implications for our understanding of the history of the Earth–Moon system. During the Apollo programme, the lunar samples were found to be devoid of indigenous water2, 3. The severe depletion of volatiles, including water, in lunar rock samples4 has long been seen as strong support for the theory that the Moon formed during a giant impact event5. Water has now been identified in lunar volcanic glasses6 and apatite7, 8, 9, but the sources of water to the Moon have not been determined. Here we report ion microprobe measurements of water and hydrogen isotopes in the hydrous mineral apatite, derived from crystalline lunar mare basalts and highlands rocks collected during the Apollo missions. We find significant water in apatite from both mare and highlands rocks, indicating a role for water during all phases of the Moon’s magmatic history. Variations of hydrogen isotope ratios in apatite suggest sources for water in lunar rocks could come from the lunar mantle, solar wind protons and comets. We conclude that a significant delivery of cometary water to the Earth–Moon system occurred shortly after the Moon-forming impact.
