评论
打印
We know that Jupiter has an atmosphere made up mainly of hydrogen and helium.
我们知道木星的大气主要由氢和氦组成。
Europa, a moon of Jupiter, has a very thin oxygen atmosphere, and HD 209458 b,
木卫二，木星的卫星，有非常稀薄的氧气大气层，还有HD 209458 b，
a Jupiter-sized exoplanet orbiting the star HD 209458 which is 154 lightyears away,
一颗木星大小的系外行星围绕着154光年远的恒星HD 209458运行，
has an atmosphere that contains hydrogen, carbon, oxygen, sodium, carbon dioxide, methane, and even water vapor.
大气中含有氢、碳、氧、钠、二氧化碳、甲烷，甚至水蒸气。
All this even though we haven’t visited any of these places to directly sample the air... but we don’t need to.
尽管我们还没有到过这些地方直接取样...但我们不需要。
We can study the air on other planets, moons, and exoplanets just by looking at them.
我们可以通过观察研究其他行星、卫星和系外行星上的空气。
In particular, by looking at light that bounces off or passes through their atmospheres,
特别是，通过观察它们的大气层反射或穿过的光，
because when you shine light on a gas, the molecules absorb and scatter different frequencies of that light in different amounts.
因为当你把光照射到气体上时，这些分子吸收和散射的光频率不同，数量也不同。
If we then split the transmitted or scattered light apart into its constituent colors using a prism or diffraction grating,
如果我们用棱镜或衍射光栅把透射或散射的光分成不同的颜色，
we can see a molecule’s light-absorption fingerprint, or its light-emission fingerprint.
我们可以看到分子的光吸收图谱，或它的光发射图谱。
This is hydrogen. This is nitrogen. Oxygen. Methane. Carbon dioxide. Water. Sulfuric acid.
这是氢。这是氮气。氧气。甲烷。二氧化碳。水。硫酸。
So when we look at the sunlight bouncing off of the atmospheres of planets and notice spikes of certain heights in certain frequencies,
所以当我们观察太阳光从行星大气层反射回来并注意到特定频率的特定高度的尖峰时，
we can carefully match those to the known fingerprints of gas molecules,
我们可以仔细地将它们与已知的气体分子图谱相匹配，
and learn not just what gases make up the air, but even their relative abundances!
不仅要了解是什么气体构成了空气，还要了解它们的相对含量！
In fact, we don’t even need to be able to see a planet at all to learn about its atmosphere –
事实上，我们甚至不需要看到某个行星就能了解它的大气层，
many exoplanets have been discovered because they pass in front of their parent star,
许多系外行星被发现是因为它们从母恒星前面经过，
which we see as a dip in the overall intensity of the star’s light.
我们看到的是恒星光总强度的下降。
But if an exoplanet has an atmosphere, the gas molecules in its atmosphere will block some frequencies an extra amount,
但如果一颗系外行星有大气层，大气层中的气体分子会额外阻断一些频率，
according to their molecular fingerprints, and we can do the same gas-matching process as before.
根据他们的分子图谱，我们可以做同样的气体匹配过程。
And that’s how we know what’s in the atmosphere of HD 209458 b!.
这就是我们如何知道HD 209458 b的大气中有什么！
Of course, in practice it’s pretty darn challenging to use molecular fingerprints to study exoplanet atmospheres,
当然，在实践中使用分子图谱来研究系外行星的大气层是相当具有挑战性的，
because air is thin so the fingerprints are super faint and we need big sensitive telescopes and spectrometers;
因为空气稀薄，所以图谱非常微弱，我们需要高灵敏度的望远镜和光谱仪；
and because atmospheres are complicated and their fingerprints can be ambiguous or hard to match;
因为环境是复杂的，他们的指纹可能是模糊的，或者很难匹配；
and because different parts of a single star emit different amounts of different colors of light,
因为一颗恒星的不同部分发出不同数量不同颜色的光，
so a planet’s effect on the star’s spectrum will depend on which part the planet passes in front of.
因此，行星对恒星光谱的影响将取决于行星从恒星前方经过的位置。
But all of these difficulties can be dealt with by clever astronomers,
但聪明的天文学家可以解决所有这些难题，
and thus we have been able to figure out what the air is like on planets hundreds of light years away that we can’t even see.
这样，我们就能弄清楚几百光年之外、我们甚至看不见的行星上的空气是什么样的。
