在一个新恒星尘盘中发现大量的水

Herschel Space Observatory 在一颗年轻的新恒星周围的尘盘的外缘发现了大量冷水蒸气。

这颗年轻的恒星名为TW Hydrae ，距地球大约是175光年，位于长蛇座（Hydra）。它的年龄大约是五百至一千万年。属于桔黄色矮星（orange dwarf star），它比我们的太阳要小，自然其表面温度也低。

1，这是艺术家的想像图。

这次天文学家们发现在这颗恒星周围的尘盘远离中心恒星的地方有大量很冷的水蒸气。这些水蒸气应当是附着在尘埃微粒外层上的冰层被该恒星的紫外线所剥离后升华而形成的。

这个巨大的尘盘环绕该恒星，有200倍地球与太阳之间的距离（AU）。天文学家们相信，在未来数百万年的时间长度里，这些尘埃会彼此碰撞和凝聚成行星，就像我们的地球家族那样。水蒸气存在的地方正是彗星形成的区域。

2，这是观测到的数据。其中的Para和Ortho水分子是指水分子中氢原子有两种自旋的名字。

这一发现说明形成地球上海洋的水在各个恒星系统中是很常见的。这些水能否在行星上形成海洋，只取决于行星及周围的物理环境的条件罢了。

这次的发现给现行的彗星形成的理论以强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证据。

这是NASA网站上新闻的原文。

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.