[揽瓜阁精读] 6. 金星氢气逃逸

小屁怡0702

Main Idea: show evidence to prove hydrodynamic escape once existed
P1: Introduce hydrodynamic escape
Most vulnerable: atmosphere rich with hydrogen
Thus, the prsent composition of an atmosphere can reveal whether this process has ever occured
P2: Previous findings of hydrodynamic escape
Hydrodnamic escape outside the solar system.
Why? A puffed-up atmosphere of hydrogen - carbon & oxygen in this inflated atmosphere - atoms too heavy to escape on their own - must have been dragged by hydrogen.
Also support: why no large planets much closer to their stars than HD is. For planets orbit within 3 million kilometer or so ..., hydrodynamic escape strips away ...
总之就是离得近的都挤兑走了
P3: 1st clue - noble gases
如果没有hydrodynamic escape, abundances should be similar, yet different.
P4: 2nd clue - radiation
Youthful stars are strong sources of ultra light, our sun was no exception. Radiation could have driven hydrodynamic escape.
P5: 3rd clue - terrestrial planets
In those days, ... steam condensed and rained back onto the surface, ... water vapor may have persisted in the atmosphere where solar radiation could break it down.
P6: Effect of hydrodynamic escape
- carry away an ocean's worth of hydrogen within a few tons of millions of years
- escaping hydrogen would have dragged along much of the oxygen but ......

lovedkyz

1、富含氢气的大气层很容易让水蒸气蒸发掉。氢气外流时会携带更重的分子和原子。就很像是沙漠的风会将尘土从【】带到【】，但留下【】和【】，因此，现在大气层的组成可以看出这个过程是否发生过。（背景）

2、实际上，天文学家在类木星的HD行星看到过氢气外逃至太阳系。用哈勃望远镜观察，Alfred和他的同事报道过行星【】。随后观测到碳元素和氧元素在大气层中。这些原子太重了无法自我逃逸因此他们必须被氢气所携带。（fact）

3、（承上启下）这个证据对于1980年氢气从原始的水星地球和金星逃逸有所证明。有3条线索推测曾发生过。
（1）惰性气体。如果没有逃逸，类似的惰性气体是不会留下来的。
（2）早期的星星是紫外线的强有力来源，太阳也不例外。这些辐射也造成了氢气逃逸。
（3）早期的陆地行星大气层富含氢气，经过太阳紫外线的辐射，化学反应，陨石和彗星的碰撞，使得充满了水蒸气。经过数千年水蒸气聚集下雨再回流到表面，但金星与太阳过近以至于水都蒸发了。

4、在这些情况下，氢气的逃逸是具备条件的。（举例）FK表明在百万年间的数十年内，金星的氢气逃逸。K后来表明氢气逃逸会携带大量的氧气但是会留下二氧化碳。二氧化碳在大气层中聚集形成了今天我们看到的金星。

Rhythmicic

dd

iririlua

Summary: The article introduces the scientific concept of Hydrodynamic Escape and presents evidence observed to explain theory of how HE works on planets to make the current atmosphere composition.

Key Structure:
P1: intro of HE and present the opinion: atmosphere today can reveal whether HE has occurred
P2: present a specific observation of HD209458b to show evidence of HE
P3: relate evidence to JFK's theory on HE in ancient Venus, Earth, and Mars with 3 clues
P4: from mentioned clues, the theory explains the composition of today's atmosphere in Venus

Key Content:
P1: 在充满氢气的大气中，氢气外逸的过程中会带走其他的分子和原子且分子原子越重，氢气外逸带走它们的速度越慢。通过这个concept，我们可以从现在的大气中观察是否曾经出现过hydrodynamic escape
P2: 观察hd209458b：这个类似于木星的行星是有富含氢气的大气的，并且通过测量发现大气中也有氧气和碳，这些原子本身太重不可能凭自身到大气中，所以必然是因为he带着这些原子分子进入大气层。同时也可以利用同样的原理解释为什么在更靠近恒星的地方不可能找到更大的行星，因为外逸的氢气可能带走一整个大气层，只留下一些remnant
P3: 上述的evidence可以用来帮助佐证1980s的关于古代金星、地球和火星he的theory，文章介绍了3个相关的clues：1) 惰性气体应该始终在大气中，如果没有发生过he，那么大气中惰性气体同位素的种类/丰富度应该和太阳大气中惰性气体的种类/丰富度一样，但是现实不是的，2）uv可以drive he，3）早起行星应该是有充满氢气的大气层的（通过水和铁的分解），当彗星跌入海洋所产生的水蒸气会在大气中，若此行星离太阳较近，则水蒸气不能凝结作为雨落下，而是会被uv分解成氢气
P4:在上述三个条件的作用下，he会发生，jfk用这个理论解释了为什么现在金星上的大气是我们今天看到的样子

XX829412

        • Hydrodynamic escape
                ○ Hydrogen flaws： drag molecules and atoms
                ○ Rate ↓，weight ↑
                ○ Present composition of an atmosphere
        • HD 209458
                ○ Inflated atmosphere: hydrogen and carbon and oxygen
                ○ Why no large planet closer:
                        §  strips away the atmosphere，scorched remnant
        • Ancient Venus, Earth and Mars
                ○ 3 clues
                        § Noble gases: abundences differ
                        § Radiation
                        § Hydrogen-rich atmosphere
                                □ Hydrogen: Chemical reaction, nebular gases ,water molecules
                                □ Steam condensed and rained back
                                        ® Venus: water vapor
                ○ 1980 hydrogendynamic in Venus: an ocean's worth of hydrogen
                ○ Sebsequently: oxygen > carbon dioxide
                        § Hellish Venus

苏二在努力

P1 atmospheres rich with hydrogen are the most vulnerable to hydrodynamic escape.
•        Hydrogen flows outward, it picks up and drags heavier molecules and atoms with it.
•        Like desert wind blow dust, hydrogen wind carries off molecules and atoms as the weight diminishes.
•        Thus: present composition of the atmosphere reveals whether this process has ever occurred.
P2 astronauts have seen the telltale signs of hydrodynamic escape outside the solar system on HD
•        Using HST, AVD reported in 2003 that the planet has a puffed-up atmosphere of hydrogen.
•        Subsequent measures: carbon and oxygen in this atmosphere
•        These atoms are too heavy to escape on their own => they must have been dragged there by hydrogen.
•        hydrodynamic loss explains: no large planets much closer to stars than HD
Buz: hydrodynamic escape strips away the entire atmosphere, leaving behind remnants.
P3 evidence of planetary winds prove the hydrodynamic escape from ancient Venus, Earth, and Mars
Three clues:
•        first, noble glass
no escape => chemically unreactive gases remain in an atmosphere indefinitely => abundances of different isotypes would be similar to original values => similar to the sun
yet, the abundances differ
•        second, young star is the source of ultraviolet light. Sun is not an exception.
•        Third, early terrestrial planets may have hydrogen-rich atmosphere
Hydrogens could come from chemical reactions of water with iron/nebular gasses/water molecules
P4 hydrodynamic escape would readily operate
•        JFK: hydrodynamic escape could have carried an ocean’s worth of hydrogen within a few ten millions of years.
•        K: escaping hydrogen dragged alone much of oxygen and left carbon dioxide
•        Without water to mediate chemicals reactions to turn into carbonate minerals, the carbon dioxide built up atmosphere and hellish Venus

D123L

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muqi10ab

难词
Molecules
atom
cobble
boulder
scorched remnant
isotopes
全文主旨：通过解释hydrodynamic escape这个现象，引出了金星上为什么会形成其独特的大气环境。
什么是hydrodynamic escape:当氢气向外吹时，它可以带走比它更重的分子和原子。为了进一步解释hydrodynamic escape作者举了三个例子: ancient Venus, Earth and Mars.

Nora小碗

dune: 沙丘
puffed-up: 充满空气的
scroch: 烧焦
lend credit to: 证实
within a few tens of millions of years： 在几千万年间
hellish：地狱一般的

VioletGTMBA

第一段：（是什么。如何辨别）与沙漠风将沙尘吹过海洋、将谷粒吹过山丘类似，氢气会带走分子和原子，并且以能减少他们重量的速度。所以根据现在的大气构成可以判断之前有无这种情况发生。

第二段：（举例子+原理1）太阳系外也有这种情况发生，之前在一个类木星上发现过。主要是天文学家在这个行星的大气内发现了系稀疏的氢气。后来又发现包括碳气、氧气。原子自身太重无法离开，所以一定是借助氢气的力量。水动力逃脱也能解释，为什么天文学家没有发现除了HD外有行星和恒星距离很近，因为气移动在亿年间带走了整个大气，只留下很少的残余物。

第三段（根据上述例子的推论1）关于行星风的证据证明了古代金星、地球和火星也发生过水动力逃。比如惰性气体，如果没发生过上述现象的话，它们会无限期的留在大气内。他们不同同位素的丰富程度应该和太阳类似。但丰富度不同于太阳。

第三段（原理2+推论2）另外，年轻的恒星是紫外线的主要来源，且太阳也不是例外，这种辐射也可能产生水动力逃脱。

Dune 山丘
Cobble 鹅卵石，圆石；
Boulder （受水或天气侵蚀而成的）巨石，巨砾
telltale 泄露内情的；n.迹象；指示器；搬弄是非者
hydrodynamicadj.水力的；流体动力学的
puffed-up adj.充满空气的；肿胀的；趾高气扬的

Scorch vt.烧焦；使枯萎；挖苦vi.烧焦；枯萎n.烧焦；焦痕
Indefinitely adv.无限期地，不确定地；（细节）不清楚地，模糊粗略地
noble gas [化学]惰性气体（等于 inert gas）