在一個新恆星塵盤中發現大量的水

Herschel Space Observatory 在一顆年輕的新恆星周圍的塵盤的外緣發現了大量冷水蒸氣。

這顆年輕的恆星名為TW Hydrae ，距地球大約是175光年，位於長蛇座（Hydra）。它的年齡大約是五百至一千萬年。屬於桔黃色矮星（orange dwarf star），它比我們的太陽要小，自然其表面溫度也低。

1，這是藝術家的想像圖。

這次天文學家們發現在這顆恆星周圍的塵盤遠離中心恆星的地方有大量很冷的水蒸氣。這些水蒸氣應當是附着在塵埃微粒外層上的冰層被該恆星的紫外線所剝離後升華而形成的。

這個巨大的塵盤環繞該恆星，有200倍地球與太陽之間的距離（AU）。天文學家們相信，在未來數百萬年的時間長度里，這些塵埃會彼此碰撞和凝聚成行星，就像我們的地球家族那樣。水蒸氣存在的地方正是彗星形成的區域。

2，這是觀測到的數據。其中的Para和Ortho水分子是指水分子中氫原子有兩種自旋的名字。

這一發現說明形成地球上海洋的水在各個恆星系統中是很常見的。這些水能否在行星上形成海洋，只取決於行星及周圍的物理環境的條件罷了。

這次的發現給現行的彗星形成的理論以強有力的支持以及地球上海洋是如何形成的研究提供新的思路和證據。

這是NASA網站上新聞的原文。

Herschel Finds Oceans of Water in Disk of Nearby Star

PASADENA, Calif. -- Using data from the Herschel Space Observatory, astronomers have detected for the first time cold water vapor enveloping a dusty disk around a young star. The findings suggest that this disk, which is poised to develop into a solar system, contains great quantities of water, suggesting that water-covered planets like Earth may be common in the universe. Herschel is a European Space Agency mission with important NASA contributions.

Scientists previously found warm water vapor in planet-forming disks close to a central star. Evidence for vast quantities of water extending out into the cooler, far reaches of disks where comets take shape had not been seen until now. The more water available in disks for icy comets to form, the greater the chances that large amounts eventually will reach new planets through impacts.

"Our observations of this cold vapor indicate enough water exists in the disk to fill thousands of Earth oceans," said astronomer Michiel Hogerheijde of Leiden Observatory in The Netherlands. Hogerheijde is the lead author of a paper describing these findings in the Oct. 21 issue of the journal Science.

The star with this waterlogged disk, called TW Hydrae, is 10 million years old and located about 175 light-years away from Earth, in the constellation Hydra. The frigid, watery haze detected by Hogerheijde and his team is thought to originate from ice-coated grains of dust near the disk's surface. Ultraviolet light from the star causes some water molecules to break free of this ice, creating a thin layer of gas with a light signature detected by Herschel's Heterodyne Instrument for the Far-Infrared, or HIFI.

"These are the most sensitive HIFI observations to date," said Paul Goldsmith, NASA project scientist for the Herschel Space Observatory at the agency's Jet Propulsion Laboratory in Pasadena, Calif. "It is a testament to the instrument builders that such weak signals can be detected."

TW Hydrae is an orange dwarf star, somewhat smaller and cooler than our yellow-white sun. The giant disk of material that encircles the star has a size nearly 200 times the distance between Earth and the sun. Over the next few million years, astronomers believe matter within the disk will collide and grow into planets, asteroids and other cosmic bodies. Dust and ice particles will assemble as comets.

As the new solar system evolves, icy comets are likely to deposit much of the water they contain on freshly created worlds through impacts, giving rise to oceans. Astronomers believe TW Hydrae and its icy disk may be representative of many other young star systems, providing new insights on how planets with abundant water could form throughout the universe.

Herschel is a European Space Agency cornerstone mission launched in 2009, carrying science instruments provided by consortia of European institutes. NASA's Herschel Project Office based at JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the U.S. astronomical community. Caltech manages JPL for NASA.