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A Large Lump of Coal

发表于 2010-3-29 16:08:27 | 显示全部楼层 |阅读模式
本帖最后由 baiseniao 于 2010-3-29 16:11 编辑

A Large Lump of Coal
source: Scientific American
Other Earths may be made of graphite and diamond BY GEORGE MUSSER

Astronomy is the science of the exotic, but the thing that astronomers most want to find is the familiar: another planet like Earth, a hospitable face in a hostile cosmos. The Kepler spacecraft, which was launched last March, is their best instrument yet for discovering Earth-like planets around sunlike stars, as opposed to the giant planets that have been planet finders' main harvest so far. Many predict that 2010 will be the year of exo-Earths. But if the giant planets, which looked nothing like what astronomers had expected, are any indication, those Earths may not be so reassuringly familiar either.
It has dawned on theorists in recent years that other Earth-mass planets may be enormous water droplets, balls of nitrogen or lumps of iron. Name your favorite element or compound, and someone has imagined a planet made of it. The spectrum of possibilities depends largely on the ratio of carbon to oxygen. After hydrogen and helium, these are the most common elements in the universe, and in an embryonic planetary system they pair off to create carbon monoxide. The element that is in slight excess ends up dominating the planet's chemistry.
In our solar system, oxygen dominates. Although we tend to think of our planet as defined by carbon, the basis of life, the element is actually a fairly minor constituent. The terrestrial planets are made of silicate minerals, which are oxygen-rich. The outer solar system abounds in another oxygen-rich compound, water.
A new study shows in detail how carbon lost out. Jade Bond of the University of Arizona and the Planetary Science Institute (PSI), Dante Lauretta of Arizona and David O’Brien of PSI have simulated how chemical elements got distributed around the solar system as it formed. They find that carbon remained in a gaseous state within the protoplanetary disk and was eventually blown out into deep space; the embryonic Earth wound up with none at all. The carbon in our bodies must have been delivered later, by asteroids and comets that formed under conditions that allowed them to incorporate the element.
Had the carbon-oxygen balance tilted the other way, Earth would have turned out very differently, as Marc Kuchner, then at Princeton University, and Sara Seager, then at the Carnegie Institution of Washington, argued in 2005. It would consist not of silicates but of carbon-based compounds such as silicon carbide and, indeed, pure carbon itself. The crust would be mainly graphite, and a few kilometers underground the pressures would be high enough to form a rigid shell of diamond and other crystals. Instead of water ice, the planet would have carbon monoxide or methane ice; instead of liquid water, it might have oceans of tar.
The galaxy could be filled with such worlds. According to an observational survey Bond cites, the average planet host star has a higher carbon-to-oxygen ratio than the sun does, and her team’s simulations predict that the most enriched systems give birth to carbon planets. “Some of these compositions differ greatly from solar and as a result produce terrestrial planets with vastly different compositions,” Bond says.
To be sure, other surveys have found that the sun is indistinguishable from the average star in its class. The Kepler spacecraft may help settle the question, because even the limited amount of information it can glean about planets—their mass and radius—is enough to tell their general composition.
Carbon Earths might be especially prevalent in more bizarre settings, such as the environs of white dwarfs and neutron stars. Regions of the galaxy that are rich in heavy elements generally, such as the galactic center, have higher carbon-to-oxygen ratios. As time passes and stars continue to manufacture heavy elements, the balance everywhere will tilt in favor of carbon.
These and other astronomical discoveries turn the tables on our notions of the familiar and unfamiliar. Most of the galaxy is dark matter; most suns are dimmer and redder than our sun; and now, it seems, other Earths may not be especially Earth-like. If anything departs from the norm and deserves to be called exotic, it is us.


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发表于 2010-3-29 16:21:00 | 显示全部楼层
Shout emperor of translation.
发表于 2010-3-29 16:21:59 | 显示全部楼层
 楼主| 发表于 2010-3-29 16:25:56 | 显示全部楼层
本帖最后由 baiseniao 于 2010-3-29 16:27 编辑

发表于 2010-3-29 16:36:57 | 显示全部楼层
Hey,two upstairs.
Pleast DO NOT use Chinese in this district.
 楼主| 发表于 2010-3-29 16:41:55 | 显示全部楼层
回复 5# qazpl-1
Well, sorry for that. Personally, I'd like to find one such planet and start mining diamond.[S::lol:]
发表于 2010-3-29 16:46:56 | 显示全部楼层
回复 6# baiseniao
Maybe you will found some anima made of diamond on that planet.
发表于 2010-3-29 16:55:12 | 显示全部楼层
回复 5# qazpl-1
Oh,sorry,I fogot that.
I hope the living creature there don`t breathe oxygen……
发表于 2010-3-29 17:01:49 | 显示全部楼层
回复 8# 尼奇怪
Maybe they are eat carbon.
Hum you're made of carbon and very soft , they will like you.~~
发表于 2010-3-29 21:28:00 | 显示全部楼层
本帖最后由 kanhf0514 于 2010-4-3 19:46 编辑

天文學是一門奇特的科學,不過各個天文學家最想找尋到的東西都是一樣: 一個跟地球相似的星球,一個在危險的宇宙裏能夠讓人容易接受的容貌。在三月發射的開普勒太空船就是他們希望在類似太陽的恆星附近,找出與地球相似的星球的最佳器材,而以往最常找尋到的就是氣體巨星。很多人預料,2010年會是「外地球」之年。不過如果那些看起來完全不像天文學家預料的氣體巨星是任何象徵的話,那些"地球"都可能不是那麼為人熟悉。

在我們的太陽系裏,氧氣是最主要的元素。雖然我們認為碳是生命的基礎,其實它只是一個較少數的成分,類地行星是由含很多氧氣的矽酸鹽所組成,而外太陽系的行星,則有著另一種含大量氧氣的物質: 水。

一個新的研究很仔細的表現出碳是怎樣失去的。美國亞利桑那州大學和行星科學研究所的Jade Bond, 亞利桑那的Dante Lauretta和行星科學研究所的David O'Brien 模擬了太陽系形成時,化學物質怎樣被分佈。他們找出碳仍然在原行星盤裏保持著氣體狀態,然後被噴出外太空。初期的地球根本沒有碳。我們身體裏的碳一定是後來被小行星和彗星在能夠讓碳與其他化學物質作用的環境下運送過來的。普林斯頓大學的Marc Kuchner和卡內基研究所的Sara Seager在2005年曾提出,如果將碳和氧的比例倒轉的話,地球會變得原全不同。地球不會由矽酸鹽組成,而是其他碳化合物如碳化矽,或者甚至是碳本身。地層主要會由石墨組成,然後地底幾公里的壓力會足夠形成一層由鑽石和其他晶體所組成的硬層。地球會有一氧化碳和甲烷冰和而不是水,甚至可能會有由焦油組成的海洋。


無可否認,其他研究找出太陽跟其他一樣級別的一般恆星沒太大分別。開普勒太空船可能可以幫助解決這個問題,因為就算它只能提供有限的資料: 質量和半徑,它都足夠讓我們知道恆星的一般成份。




参与人数 2UCC +100 好评 +1 贡献 +1 收起 理由
qazpl-1 + 1 Good job!
baiseniao + 100 + 1 大赞!翻译得很精彩!受教了。 ...


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