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  • The universe contains about 100 billion galaxies.

    宇宙中大約有1000億個星系。

  • Each of those galaxies contains about 100 billion stars.

    這些星系中的每一個都包含了大約1000億顆恆星。

  • Many of those stars have planets orbiting them.

    其中許多恆星都有行星圍繞著它們運行。

  • So how do we look for life in all that immensity?

    那麼,我們該如何在這無量無邊中尋找生命呢?

  • It's like searching for a needle in trillions of haystacks.

    這就像在數萬億個大海撈針一樣。

  • We might want to focus our search on planets that we know can support life as we know it --

    我們可能想把搜索重點放在我們知道能支持生命的星球上...

  • what we call habitable worlds.

    我們稱之為可居住的世界。

  • What do such planets look like?

    這樣的行星是什麼樣子的?

  • To answer that question, we don't look out there.

    回答這個問題,我們不看外面。

  • Instead, we look at ourselves. At Earth.

    相反,我們看著自己。在地球上。

  • Because this is the one planet in the universe that we know for certain is habitable.

    因為這是宇宙中唯一一個我們可以確定是適合居住的星球。

  • When we look at Earth from space, we see a blue, watery world.

    當我們從太空看地球時,我們看到的是一個藍色的、水汪汪的世界。

  • It's no coincidence that three quarters of the surface is covered by oceans.

    這不是巧合,四分之三的地表被海洋覆蓋。

  • Because of its unique chemical and physical properties,

    由於其獨特的化學和物理特性。

  • water is absolutely essential for all life as we know it.

    水對於我們所知的所有生命來說絕對是必不可少的。

  • And so we get especially excited about other worlds on which water is abundant.

    所以我們對其他水豐富的世界特別興奮。

  • Fortunately, water is very common in the universe.

    幸運的是,水在宇宙中很常見。

  • But life needs water in the form of liquid, not ice, and not vapor,

    但生命需要的是液體形式的水,而不是冰,也不是蒸汽。

  • and that's a little bit less common.

    而這'就有點不太常見了。

  • For a planet to have liquid water at its surface, three things are important.

    一個星球要想在其表面有液態水,有三件事很重要。

  • First, the planet needs to be large enough that the force of gravity

    首先,行星需要足夠大,引力的力量

  • keeps the water molecules from flying off into space.

    讓水分子不至於飛向太空。

  • For example, Mars is smaller than Earth, and so has less gravity,

    例如,火星比地球小,所以重力較小。

  • and that's one important reason that Mars has a very thin atmosphere,

    而這也是火星大氣層非常稀薄的一個重要原因。

  • and no oceans at its surface.

    而在其表面沒有海洋。

  • Second, the planet needs to have an atmosphere. Why?

    第二,地球需要有大氣層。為什麼?

  • Because without an atmosphere, the planet is in a vacuum,

    因為沒有大氣層,地球就處於真空狀態。

  • and liquid water isn't stable in a vacuum.

    而液態水在真空中並不穩定。

  • For example, our moon has no atmosphere, and so if you spill some water on the moon,

    比如說,我們的月球沒有大氣層,所以如果你在月球上灑一些水。

  • it will either boil away as vapor, or freeze solid to make ice.

    它要麼以蒸汽的形式沸騰,要麼凝固成冰。

  • Without the pressure of an atmosphere, liquid water can't survive.

    沒有大氣的壓力,液態水就無法生存。

  • Third, the planet needs to be at the right distance from its star.

    第三,行星與恆星的距離要合適。

  • Too close, and the surface temperature will exceed the boiling point of water,

    過近,表面溫度會超過水的沸點。

  • and oceans will turn to vapor.

    和海洋將變成水汽。

  • Too far, and the surface temperature will fall below the freezing point of water,

    太遠,地表溫度就會降到水的冰點以下。

  • causing the oceans to turn to ice.

    導致海洋變成冰。

  • Fire or ice. For life as we know it, neither will suffice.

    火或冰。對於我們所知的生命來說,兩者都不夠。

  • You can imagine that the perfect zone where water stays liquid looks kind of like a belt around a star.

    你可以想象一下,水保持液態的完美區域看起來有點像圍繞著恆星的一條帶子。

  • We call that belt the habitable zone.

    我們稱那條帶子為可居住區。

  • So when we search for habitable worlds, we definitely want to look for planets in the habitable zones around their stars.

    所以我們在尋找宜居世界的時候,一定要在恆星周圍的宜居區尋找行星。

  • Those regions are the best bets to find planets like Earth.

    這些地區是尋找像地球這樣的行星的最佳選擇。

  • But while habitable zones are a pretty good place to begin the search for planets with life,

    但是,雖然宜居區是一個相當不錯的地方,可以開始尋找有生命的行星。

  • there are a couple of complications.

    有幾個併發症。

  • First, a planet isn't necessarily habitable just because it's in the habitable zone.

    首先,一個星球不一定適合居住,只是因為它'在可居住區。

  • Consider the planet Venus in our solar system.

    考慮到太陽系中的金星。

  • If you were an alien astronomer, you'd think Venus is a pretty good bet for life.

    如果你是一個外星天文學家,你'會認為金星是一個相當不錯的生命賭注。

  • It's the right size, it has an atmosphere, and it's in the habitable zone of our sun.

    它大小合適 有大氣層 而且在太陽的可居住區裡

  • An alien astronomer might see it as Earth's twin.

    外星天文學家可能會把它看作是地球的孿生兄弟。

  • But Venus is not habitable, at least not at its surface.

    但金星不適合居住,至少在其表面不適合居住。

  • Not by life as we know it. It's too hot.

    不是由我們所知道的生活。它太熱。

  • That's because Venus' atmosphere is full of carbon dioxide, an important greenhouse gas.

    那是因為金星'大氣中充滿了二氧化碳,這是一種重要的溫室氣體。

  • In fact, its atmosphere is almost entirely carbon dioxide,

    事實上,它的大氣中幾乎全是二氧化碳。

  • and is almost 100 times thicker than our own.

    並且比我們自己的厚度幾乎厚100倍。

  • As a result, the temperature on Venus is hot enough to melt lead,

    是以,金星上的溫度足以融化鉛。

  • and the planet is dry as a bone.

    而這個星球卻乾枯如骨。

  • So finding planets of the right size and distance from their stars is only a beginning.

    所以,尋找大小合適、距離恆星距離合適的行星只是一個開始。

  • We also want to know about the makeup of their atmospheres.

    我們也想知道他們大氣層的構成。

  • The second complication emerges when we look a little more deeply at planet Earth.

    當我們更深入地觀察地球時,就會發現第二個複雜問題。

  • In the last 30 years, we've discovered microbes living in all sorts of extreme environments.

    在過去的30年裡,我們'發現了生活在各種極端環境中的微生物。

  • We find them in fissures of rock miles beneath our feet,

    我們在腳下數英里處的岩石裂縫中找到它們。

  • in boiling waters of the ocean floor,

    在沸騰的海底水裡。

  • in acidic waters of thermal springs,

    在酸性溫泉水中。

  • and in cloud droplets miles above our heads.

    並在我們頭頂數英里的雲滴中。

  • These so-called extremophiles aren't rare.

    這些所謂的極端分子並不罕見。

  • Some scientists estimate that the mass of microbes living deep underground

    據一些科學家估計,生活在地下深處的微生物的品質。

  • equals the mass of all the life at Earth's surface.

    等於地球表面所有生命的品質'。

  • These subterranean microbes don't need oceans or sunshine.

    這些地下微生物不需要海洋和陽光。

  • These discoveries suggest that Earth-like planets may be only the tip of the astrobiological iceberg.

    這些發現表明,類地行星可能只是天體生物學冰山的一角。

  • It's possible that life might persist in aquifers beneath the surface of Mars.

    它'生命有可能存在於火星表面下的含水層中。

  • Microbes may thrive on Jupiter's moon Europa,

    微生物可能在木星'的衛星歐羅巴上茁壯成長。

  • where liquid water ocean probably lies beneath the icy crust.

    其中液態水海洋可能位於冰殼之下。

  • Another ocean beneath the surface of Saturn's moon Enceladus is the source of geysers erupting into space.

    土星'的衛星恩克拉多斯表面下的另一片海洋是向太空噴發的噴泉的來源。

  • Could these geysers be raining microbes?

    難道這些間歇泉是在下微生物雨?

  • Could we fly through them to find out?

    我們能不能飛過他們去看看?

  • And what about life as we don't know it, using a liquid other than water?

    那我們不知道的生命呢',使用水以外的液體?

  • Maybe we are the crazy creatures living in an unusual and extreme environment.

    也許我們是生活在不尋常的極端環境中的瘋狂生物。

  • Maybe the real habitable zone is so large

    也許真正的可居住區就是這麼大

  • that there are billions of needles in those trillions of haystacks.

    在那數萬億個乾草堆裡有數十億根針。

  • Maybe in the big scheme of things, Earth is only one of many different kinds of habitable worlds.

    也許從大的方面來說,地球只是許多不同種類的可居住世界中的一個。

  • The only way to find out is to go out and explore.

    唯有走出去探索,才能找到答案。

The universe contains about 100 billion galaxies.

宇宙中大約有1000億個星系。

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B1 中級 中文 美國腔 TED-Ed 行星 大氣層 地球 海洋 生命

【TED-Ed】 在無數草堆裡的一根針: 尋找適合居住的世界 A needle in countless haystacks: Finding habitable worlds - Ariel Anbar

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    Furong Lai 發佈於 2012 年 11 月 30 日
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