过去我们所认识的行星 It used to be the only planets we knew about
只限于围绕我们太阳系内的那几个 were the ones that orbit our sun.
现在才发现 But now we've discovered
另有岩质行星与气态行星 rocky worlds and gas giants
围绕其它恒星运转 orbiting other stars.
它们各有奇妙身世 They tell an amazing story.
这些行星早期是非常狂暴不安 The early history of these planets would have been very, very violent
各处行星的诞生方法如出一辙 Planets are made everywhere in the same way.
由恒星诞生所遗下的尘与瓦砾聚成 They form from the dust and debris left over from the birth of stars.
既然形成方法相同 So if they're all made the same way,
何以又面貌各异? what makes them all so different?
宇宙有道理 How the Universe Works
第1季第6集：行星 Planets
宇宙间有许许多多的银河系 The universe is full of galaxies,
气体云 gas clouds,
恒星 stars,
原来还有许多行星 and planets, as it turns out.
我们的太阳系有八颗行星 Our solar system has eight planets.
但与银河系内整个行星大家族相比 But we now know they're a tiny group,
实在是小巫见大巫 compared to the huge cosmic family of planets across the galaxy.
这是科学史上一个异乎寻常的时刻 It's an extraordinary moment in scientific history
我们确知外面还有别的行星系 to know, for sure, that there are other planetary systems out there.
极其普遍 They're very common.
我们银河系里有二千亿颗恒星 And out of the 200 billion stars in our Milky Way galaxy,
肯定也有数百亿颗的行星 there are surely dozens of billions of planets out there.
2009年 In 2009,
太空总署发射开普勒太空望远镜 NASA launched the Kepler space telescope
升空六年, 寻找系外行星 on a six-year mission to find new planets orbiting other stars.
迄今发现了四百多颗 So far, astronomers have found over 400.
好些是翻腾不息的庞大气团 Some are colossal balls of churning gas,
体积五倍于木星 five times the size of Jupiter.
别的是比地球大许多倍的岩质行星 Others are huge, rocky worlds many times larger than Earth.
好些的轨道飘忽无定 Some follow wild, erratic orbits,
因贴近恒星而燃烧起来 so close to a star they're burning up.
有一点再明白没有 One thing is clear,
没有两颗行星是一模一样的 no two planets are the same.
每一颗都是独一无二 Each is one of a kind.
但新发现的行星遥远而难以探究 But most of these new planets are far away and hard to study.
我们对行星运作的了解 Most of what we know about how planets work
主要来自我们太阳系内的八颗行星 comes from the eight that orbit our own star.
我们的系内行星分为两大类: Our own planets come in two main types.
内太阳系的四颗岩质行星: There are four rocky planets in the inner solar system:
水星 Mercury.
金星 Venus.
地球 Earth.
还有火星 And Mars.
另有是外太阳系的四颗气态行星: And in the outer solar system, there are four giant gas planets:
木星 Jupiter.
土星 Saturn.
天王星 Uranus.
还有海王星 And Neptune.
八颗行星面貌各异, 大不相同 Each of the eight planets is distinct and very different.
行星的特性早在46亿年前 Their unique personalities began to form at the birth of our solar system,
太阳系诞生之际已然形成 4.6 billion years ago.
太阳燃烧, 留下一团巨大气尘云 When the sun ignited, it left behind a huge cloud of gas and dust.
岩质行星与气态行星合共八颗行星 All eight planets, the inner rocky and the outer gas planets
都是来自这一团宇宙残余物质 came from this cloud of cosmic debris.
太阳系的行星无不脱胎自同一物质 The planets in ocr solar system are all made from the same stuff.
脱胎自同一团气尘云 They're made from the same cloud of gas and dust,
却在不同的环境下合成 but they formed under very different conditions.
部分在邻近太阳的高温地区形成 Some of them formed in close to the sun, where it was much hotter,
部分在远离太阳的低温地区形成 some much farther away, where it was much colder.
因为环境迥异 And because the conditions were so different,
形成的结果也各不相同 the end result, the product of their formation, was, was different as well.
依我看法, 太阳系的开始 So you start the solar system, in my view,
源自同一团的硅酸盐、水蒸汽 with a pretty homogeneous mix of silicates and water vapour
大量氢气与甲烷与别的元素 and hydrogen, lots of hydrogen, and methane and other elements.
尘云里的元素好比做蛋糕的材料 These elements in the dust cloud are like ingredients in a cake.
用相同材料能烘成不同的蛋糕 They cook differently,
取决于材料的配搭与炉温的高低 depending on the combination of the ingredients and the temperature of the oven.
就像做蛋糕, 把材料混和 And just like with the cake, you'd mix the ingredients.
送入炉里烤烘, 受热而变质 And then you'd put it in the oven and bake it, and it would change.
太阳系里也是同一原理 And so this is kind of what happened in the solar system.
每个行星的受热情况不同 Overall, the planet cooks in a slightly different way,
视乎距离太阳的远近 depending on how close it is to the sun.
距离相近, 热力高 Close in, where it's hot,
太阳会烧掉气体和水分 the sun burns off gases and boils away water.
唯有高温下仍能保留固态的物质 Only materials that stay solid at high temperatures,
诸如金属和岩石 like metals and rock,
才得以保留 can survive,
这就是为什么靠近太阳的行星都是岩质行星 which is why only rocky planets form close to the sun
远离太阳热力的地方 Move farther away from the heat of the sun,
就换成另一种烹调行星的手段 and you get different kinds of planets cooking.
不过究竟会形成哪一类行星 But it's the ingredients in the cloud
还要看云团里有甚么材料而定 that determine precisely what kinds of planets will form.
这要看形成太阳系的是哪种星云 Well, depending on the type of cloud a solar system forms in,
有些太阳系根本没有岩质行星 you could have solar systems that don't have rocky planets
正是缺乏形成地球这类行星的物质 because it was just too poor in the materials to build something like the Earth,
结果只会形成更多气态巨行星 and instead you could end up with more gas giants
反而一颗岩质行星也没有 and, and no rocky planets at al
要有岩质行星 If you want rocky planets,
先要有一团满是金属和岩石的星云 you need a cloud full of metals and rock.
下一步, 降温 Next step, turn the heat down.
温度下降时, 那里面沸点高的元素 As it cools down, some of the elements in there that have a high boiling point
开始凝成固体 start to condense out as solids.
于是形成许多微小的矿粒 And you can get these very tiny little mineral grains forming.
这些小矿粒是孕育岩质行星的种子 These tiny mineral grains are the seeds of a new rocky planet
假以时日, 小矿粒聚合 Over time, they start to stick together.
一个尘分子与另一个尘分子 You have one dust molecule and another dust molecule,
基本上就是撞在一起 and they would basically slam into each other,
形成一个稍大一级的尘分子 and become one slightly bigger dust molecule.
它们吸收越来越多的分子 And they would pick up more and more and more.
这个步骤名叫吸积 This process is called accretion.
这些东西陆续增大, 变成岩石 As these things got bigger, they became basically rocks.
之后岩石相撞, 形成巨石 Then rocks slam into other rocks and form boulders-
巨石相撞, 形成更大的巨石 Boulders smash together to form bigger boulders.
最后, 结聚至相当体积 Eventually, you've got something big enough
本身已有足够引力把物质牵引过来 that its gravity was strong enough, that it could start drawing material in.
于是再不用以相撞来增加质量 So instead of just slamming into material and gaining mass that way,
而是主动把物质牵引过来 it was actually actively pulling material in.
在我们的太阳系里 In our own solar system,
初时有许多初生行星, 也许上百颗 there were many growing infant planets at first, maybe a hundred.
但大部分长不大 Most of them didn't make it.
要是看看小行星带里的灶神星 If you go to the asteroid belt and look at the asteroid 4 Vesta,
就可知道岩质行星要有多大 that is a good indicator of how big a rocky planet has to be
才能把自己塑成球体 before it can pull itself into a spherical shape.
灶神星宽才329英里 Vesta is only 329 miles across
不足以形成球体 not quite big enough to become a sphere.
行星要增长至500英里宽才得成球体 For a growing planet to become round, it has to reach 500 miles across.
如此才有足够引力把自己压成球状 Then it has enough gravity to crush it into a sphere.
500哩以下只能维持不规则形状 Any smaller, and it stays an irregular shape.
圆形的初生行星不断吞并物质 As round infant planets keep eating up stuff,
每次撞击都进一步加热 each collision makes them hotter and hotter
直至开始融化 until they start to melt.
现在引力开始分隔轻、重物质 Now gravity begins to separate the heavy stuff from the light
较轻的物质浮起, 形成一层硬壳 Lighter materials tend to float up into crusty film,
较重的物质, 许多是金属 and the heavier materials, many of them metals,
下沉形成高密度的行星核心 falling down and forming a much denser core at the centre of the planet
年轻行星终于现出行星雏型 The young planets are finally beginning to look like planets.
但接着又要经历连番的猛烈冲击 But now they have to survive a period of violence and destruction,
这个残酷阶段将决定哪个行星生存 a brutal phase that determines which planets will live
哪个行星灭亡 and which planets will die.
太阳诞生之后 After the birth of the sun,
同一团气尘云衍生我们的八颗行星 our eight planets all evolved from the same cloud of dust and gas,
但最后结果又截然不同 and yet they ended up completely different
新生行星并没有甚么常规可依 There was no real blueprint for each of the newborn planets.
诚然要受物理定律和化学定律规范 They did obey the laws of physics and chemistry,
但要紧关头又纯粹是机缘巧合 but the most important things happened by pure chance.
45亿年前 4.5 billion years ago,
大约一百颗初生行星围绕太阳 around 100 baby planets circled our sun.
随后上演一场碰碰车大赛 It turned into a demolition derby.
行星撞行星, 大部分被毁 Planet hit planet. Most were destroyed.
这些行星 The early history
的早期要遭受到各种暴力 of these planets would have been very, very violent,
每颗行星来到最后成长阶段 with lots of these impacts taking place
都要承受许多撞击 in the final stages of the growth of each planet.
撞击起来, 物体互相碰撞 As these impacts took place, as objects ran into each other,
芸芸星子之中 certain objects began to grow at the expense of all the others
部分会不断并吞而壮大 in this swarm of planetesimals.
这些行星, 这些准行星 And these planets, these things that would become planets,
不断增长, 越来越大 grew and grew, and as they got bigger,
它们横扫周围比自己小的星子 they swept up all the smaller planetesimals around them,
于是那颗原行星的表面 the consequence on the surface of that protoplanet
受到来自太空的碎片的大规模轰炸 being an enormous amount of bombardment by debris from space.
轰炸过后 When it was over,
只剩下四颗各不相似的岩质行星 all that was left were four very different rocky planets.
每颗行星都留下饱受轰炸的印记 Each planet's impact history left its stamp,
所以它们各不相同 and that's why they're all so different from each other.
火星是一片冰雪荒原 Mars is a frozen wasteland.
地球有液态水流动 Earth flows with liquid water.
金星是一片火山地狱 Venus is a volcanic hellhole.
水星细小、苍凉、热不可耐 And Mercury is tiny, bleak and super hot,
那是经受一次惊天动地撞击的结果 the result of a monster collision.
以水星为例, 水星密度高而地壳薄 Mercury, for example, is extremely dense and has a very thin crust.
原本可能是一个较大的行星 So it's possible it started off as a bigger planet.
后来受外物侧面撞击 And then something hit it at an angle,
撞去轻身外壳, 余下高密度的核心 and it sheared off the lighter-weight crust, leaving only the dense core.
成长中的地球也受过猛烈冲击 The young Earth also took a big hit.
发育阶段晚期, 地球与外物碰撞 Sometime late in its development, the Earth was impacted by another object
地球地幔里的瓦砾也飞了出来 that ripped debris out of the Earth's mantle
落入围绕地球的轨道 which then went into orbit around the Earth
再逐步积聚而成今天的月球 and re-accumulated to form what is now the moon.
也有证据显示火星受过撞击 There's also evidence that something crashed into Mars.
火星北半球的地壳比南半球薄 The Northern Hemisphere has a thinner crust than the Southern.
有一派理论解释说 A theory that has emerged for how this happened
火星形成之初 is that early in the planet's history,
有物件撞击火星的北半球 the Northern Hemisphere of Mars was whacked by some object
大量地壳碎片弹出 that blasted a lot of the crust off of it.
碎片在火星的南半球重新积聚 And that crust re-accumulated on the southern half of Mars.
这类撞击带来两个后果: All these collisions did two things.
生存下来的初生行星数目减少 They cut down the number of surviving infant planets.
同时为生还行星带来更多材料 And they brought more ingredients to the survivors.
要是与富含金属的物件相撞 If you had a collision with something that was metal-rich,
金属碎片会往下沉, 形成核心 those chunks would tend to descend down into what was becoming the core
要是与轻身物质或冰块撞碰 where if you collided with something light or icy,
它们会向上浮, 形成外壳 they would tend to just float about and form part of the crust instead.
接近太阳的四颗岩质行星将近完成 The four rocky planets close to the sun were almost complete.
核心是高热的固态铁 They had a solid, hot-iron core
外罩一层液态铁 surrounded by a layer of liquid iron,
上面再包一层熔岩 all wrapped in a jacket of molten rock.
熔岩之上就是地壳 Above that, an outer surface crust.
岩质行星的基本结构相同 These rocky planets all formed in the same basic way,
基本素材也相同 from the same basic stuff.
但它们又各有差异 But each of them was very different.
大小不一, 命运更有天壤之别 Different sizes and very different destinies.
太空看似空无一物 Space may look empty
其实不然 but it's not
内里充满太阳喷出来的物质 It's full of stuff blown out of the sun.
太阳产生强盛磁场 The sun generates powerful magnetic fields
磁场如一个一个巨环由表面喷出 that rise above the surface in giant loops.
碰撞时 When they clash,
触发一道超热的带电粒子流 it triggers a storm of super hot, highly-charged particles
向太空喷发 blasting out into space.
是为太阳风 It's called the solar wind.
太空里的航天员看得见太阳风 Astronauts in space can see it.
但要闭上眼睛才得见 But only when they close their eyes.
偶然, 闭上眼睛会看见一点闪光 Occasionally, you see a little flash with your eyes shut.
那是活跃粒子钻入你头部 And that is an energetic particle coming through your head
与你眼睛内的液体发生作用 and interacting with the fluid inside your eye,
形成那点闪光 and it makes a little light flash.
几分钟看见一次 And you see these every couple of minutes or so,
要是你闭上眼睛又未睡去 that you're awake with your eyes shut.
航天员接触太阳风过量 If the astronauts were exposed to a lot more of the solar wind,
可以致命 it could be a killer.
太阳神计划期间 During the Apollo programme,
两次登月任务之间曾爆发太阳风 in between two of the moon missions, there was an outburst on the sun
当时若有航天员在太空, 可能送命 that would have killed the astronauts if they had been there.
太空辐射可不是儿嬉的 So space radiation is a serious business.
但回到地球, 太阳风并不构成威胁 But here on Earth, the solar wind isn't much of a threat
因为我们有无形罩保护 because we have an invisible protective shield,
就是地球核心产生的磁场 a magnetic field generated by the planet's core.
地球中心是一个固体内核 The very centre of the Earth is the solid inner core.
是一个坚实的铁晶球 It's a hard, iron, crystalline ball.
外面厚厚一层液态铁不断对流滚动 Then there's a thick layer of liquid iron, which is convecting churning motions,
由此衍生磁场 which give rise to the magnetic field.
理论是那样说 Well, that's the theory.
为了证实铁质地核能产生磁场 To prove that an iron core can generate a magnetic shield,
科学家在实验室里自制行星 scientists built their own planet in a lab.
这个直径10尺, 重量26吨的球体 This 10-foot, 26-tonne sphere
模拟地球深处的环境 simulates conditions deep inside the Earth.
中心的金属球就是地球的核心 A metal ball in the centre acts as the planet's inner core.
周围有液态钠以90哩时速运转 Liquid sodium spins around it at 90 miles an hour,
模仿液态金属围绕地核运转的作用 imitating the effects of molten metal spinning around the Earth's core.
设计这个实验是要尝试制造磁场 We built this experiment to try to generate a magnetic field,
试图了解 to attempt to understand why the Earth has a magnetic field
地球为什么会有磁场 why the Earth has a magnetic field
而别的行星却没有磁场 and why other planets do not have magnetic fields.
运作起来就像汽车的发电器 It works like the generator in your car,
用盘卷的电线产生电力 where rotating coils of wire produce electricity.
实验中, 液态钠围绕核心滚动 In the experiment, liquid sodium churns around the core
产生磁场 and generates a magnetic field.
它与发电机大同小异 it's very much like an electrical generator.
制造动力来产生磁场 You have motion that is able to generate magnetic fields
把能量、动能转化为磁能 by turning the energy, the motion, into magnetic energy.
地球深处的动态一样 The same thing happens deep inside the Earth.
地球转动时 As the Earth spins,
液态铁围绕固体核心流动 the hot liquid metal flows around the solid core,
把能量转化为磁场, 由两极逸出 transforming its energy into a magnetic field that emerges from the poles.
磁场替地球挡开了太阳风 It protects the planet's atmosphere from the solar wind.
要是行星有磁场 And if the planet has a magnetic field,
就会把太阳风导走, 绕过行星 that solar wind will be diverted around the planet by the magnetic field.
磁场让太阳风转向, 偏离地球而去 The magnetic field deflects the solar wind around the planet,
保护地球的大气层与地球表面万物 protecting the atmosphere and everything on Earth's surface.
有时太阳辐射风暴与磁场交缠起来 Sometimes big storms of solar radiation will mix it up with the magnetic field.
就会在两极爆发出灿烂炫目的极光 Then we get big light shows over the poles, the auroras.
没有磁场 Without a magnetic force field,
太阳风会吹走地球的大气层与水 the solar wind would blast away Earth's atmosphere and water,
留下一个生机绝灭的行星 leaving a dead, arid planet,
就似火星 a lot like Mars.
火星的形成过程与地球无异 Mars formed just like Earth.
但今天的火星冰冷干涸, 大气稀薄 But today, it's cold and dry with little atmosphere.
两颗行星何以有那么大的差别? So why are the two planets now so different?
2004年 In 2004,
太空总署派出两架火星探测器 NASA sent two robot explorers to Mars to find out.
探测器名叫精神号与机会号 The rovers, named Spirit and Opportunity,
在火星表面探索了许多哩 explored miles of the Martian surface.
证实火星是干涸而难以生存的荒漠 They confirmed that Mars is a dry and hostile desert,
大气层只及地球的1% with only one percent the atmosphere of Earth.
但它们也找到火星曾经有水的遗迹 But they did find evidence of water in the past.
火星不是自始就是荒漠 Mars was not always a desert.
我们找到有力证据 We have found compelling evidence
证明火星曾经有水 that water was once beneath the surface,
冒出地面后就蒸发无踪 came to the surface, and evaporated away.
我们在几处地方看见波纹遗迹 We also see in a few places ripples
就是水流过沙土留下的纹路 preserved of the sort that are formed when water flows over sand.
所以不独地下有水, 表面也有水流 So not only did water exist below the surface, it had flowed across the surface.
要是火星以前有水 If Mars had water once,
多半以前也有厚重的大气层 it probably also had a thick atmosphere.
那么发生了甚么事? So, what happened?
我们看得出火星曾经有活火山 We can see that Mars once had active volcanoes.
意味以前也有滚热的地心 So it had a hot interior at some point
因为火星与地球都以同一材料构成 And because it was made of the same stuff as Earth,
所以也有一个热铁地核 it would have had a hot-iron core,
再由液态铁包围 surrounded by liquid metal at its centre.
故此火星也该有磁场 So it should have had a magnetic field too.
问题是: 磁场哪里去了? The question is, where did it go?
火星形成初期, 似乎具有强力磁场 Early in the planet's history, Mars apparently had a strong magnetic field.
来由大概与地球的相同 And it was probably caused in the same way as it is on Earth.
只是火星比地球小 But Mars is a smaller planet than Earth.
是以热力流失得快 It's gonna lose its heat more rapidly as a consequence.
热力流失, 液态核心就会凝固 And what that means is that liquid core can freeze solid.
核心凝固, 对流也就终止 Freeze the core solid, the convection will stop.
对流终止, 磁场也就消失 The convection stops, the magnetic field goes away.
磁场一去 As the magnetic shield died,
大气层给太阳风刮走, 水分蒸发 the solar wind blasted away the atmosphere and the water evaporated.
火星顿变冷冰冰的绍地 Mars became a cold, barren planet.
火星 Mars
地球 Earth
金星 Venus
水星 Mercury
都是岩制行星 the rocky planets,
全都在太阳1.5亿哩内形成 all formed within 150 million miles of the sun.
但四倍距离之外 But four times farther out,
太阳炮制了另一类行星 the sun baked a very different kind of planet
这批庞然大物由气体构成 They're gigantic, they're made of gas,
这些怪兽 these monsters
at no solar services at all
迄今, 航天员新发现四百多颗行星 So far, astronomers have discovered over 400 new planets
围绕其它遥远的太阳系运转 orbiting in far-off solar systems.
它们几乎全都是气态巨行星 Nearly all of them are gigantic and made of gas.
我们的太阳系也有四颗气态巨行星 We have four of these so-called gas giants in our own solar system.
木星、土星、天王星、海王星 Jupiter, Saturn, Uranus, Neptune.
各有一层稠似浓汤的厚厚大气层 Which all have these very thick, very soupy
大气层里有大量氢气、大量氦气、大量甲烷 atmosphere lots of hydrogen, lots of helium, lots of methane.
何以外行星气态? 内行星岩质? Why are these outer four made of gas when the inner ones are rocky?
关键全在位置 It all has to do with location.
距离太阳五亿英里的地方冰冷奇寒 Out here, 500 million miles from the sun, it's very cold.
太阳系诞生之初, 有尘土 At the start of the solar system, there was some dust,
但主要是气体和水, 凝结成冰粒 but mostly, gas and water, frozen in ice grains.
那些巨行星初成时, 非常冷以至于雪都是固态的 Where the giant planets started to form, it was cold enough to get solid snow.
估计会形成雪花 And we think we were able to make ice snowflakes,
雪花结聚, 成为巨行星的核心 and these things were able to clump together to form the cores of the giant planets.
巨行星因此变成那么巨大 And we think that's maybe why the giant planets got to be so big.
当时冰与气体充斥, 核心越来越大 There was so much ice and gas their cores grew huge,
十倍于地球 around 10 times larger than the Earth.
巨型核心产生强大引力 These giant cores generated a lot of gravity.
拉力强横, 把周围的气体尽吸进去 They had so much pulling power, they sucked in all the surrounding gas
积聚成几万哩深浓汤似的大气层 and built up thick, soupy atmospheres tens of thousands of miles deep.
行星越大, 引力越强 The larger they got, the more gravity they generated.
更多的尘与瓦砾给扯向行星 More and more dust and debris got pulled in towards the planets,
遂成为孕育卫星的素材 and this became the building blocks of their moons.
木星与土星各有六十多颗卫星 Jupiter and Saturn have over 60 moons each.
气态行星还有另一个特色: The gas planets have another special feature:
行星环 rings.
土星那瑰丽的行星环虽是一枝独秀 Saturn is unique among the planets in that has this gorgeous ring system.
其实木星、天王星与海王星也有环 It turns out Jupiter and Uranus and Neptune, they have ring systems, as well.
只是薄弱稠零, 难以察觉 but they're really weak and pathetic and extremely hard to detect.
但的而且确有环 But they are there.
四颗气态巨行星均有行星环 All four of the gas giants have rings,
但以土星的最为夺目 but Saturn's are the most obvious.
土星环远看如一只扁平圆碟 From a distance, Saturn's rings look like a single flat disk.
其实土星环是由几千个小环聚成 However, they're actually thousands of separate ringlets,
每一个才几哩宽 each only a few miles wide.
探测器卡西尼号掠过时 When the Cassini probe flew past,
探索到数十亿的冰块与宇宙瓦砾 it detected billions of pieces of ice and cosmic rubble
在环内以高达五万哩的时速运转 orbiting inside the rings at speeds of up to 50,000 miles an hour.
这些冰块与石块不时互相碰撞 These bits of ice and rock constantly crash into each other.
有些形成小卫星, 有些撞个碎散 Some grow into tiny moons, others smash apart.
但决不会发展成为大型卫星 But they never form into larger moons
因为早已被土星的巨大引力扯开 because Saturn's immense gravity tears them apart.
行星环究竟如何形成 Scientists are only just beginning to figure out
科学家也只是刚有头绪 how the rings formed in the first place.
理论是这样的: The theory goes like this:
一颗彗星撞进一颗卫星 a comet smashed into a moon
把它撞出轨道, 于是更接近行星 and knocked it out of its orbit and closer to the planet.
土星的引力把它撕成碎块 Saturn's gravity tore it to pieces.
瓦砾就此滞留在围绕行星的环内 And all of that debris got trapped in rings around the planet
但气态巨行星的真正疑团 But the real mysteries of the gas giants lie deep inside them,
埋在云下几万哩的行星深处 tens of thousands of miles beneath the clouds.
那里才是活动枢纽 This is where the real action is.
环境极端得要挑战自然规律 It's a place so extreme it challenges the laws of nature.
我们新发现的系外行星 Most of the new planets we're finding around distant stars
以气态巨行星为主 are gas giants.
巨大得木星相形见绌, 变了侏儒 They're so huge they make Jupiter look small.
但不论是系外的还是系内的 But what goes on inside all gas giant planets,
气态巨行星的内在动态仍然是谜 both in our solar system and way out there, is a mystery.
我们知道木星的大气层深四万哩 We know Jupiter's dense atmosphere is 40,000 miles deep,
我们得见高速运转的气体带 and we can see high-speed bands of gas
在木星表面刮起剧烈风暴 creating violent storms that rage across its surface.
但无从看穿风暴之下是甚么景象 But what we don't know is what's going on deep inside, far beneath the storms.
为一探究竟 To find out,
太空总署派遣伽利略号探测木星 NASA launched the spacecraft Galileo
为期14年 on a 14-year mission to Jupiter.
阿特兰蒂斯号与伽利略号点火升空 We have ignition and lift-off of Atlantis and the Galileo spacecraft
飞赴木星 bound for Jupiter.
1995年12月7日 December 7, 1995.
伽利略号发射探测车 Galileo dropped a probe
以16万哩时速坠落木星的大气层内 that dove into Jupiter's atmosphere at 160,000 miles an hour.
进入大气层后以降落伞减速 Parachutes slowed it down as it dropped through the thick atmosphere.
探测车在云层里探测到闪电 It detected lightning in the clouds
还有时速450哩的强风 and winds of 450 miles an hour.
探测车地球传送数据仅58分钟 The probe transmitted data back to Earth for 58 minutes.
大家追问落入大气层的探测车怎样 So people have asked me what happened to the Galileo probe that we dropped in?
它没有撞中甚么 !t didn't hit anything.
只是一路深入木星里去 It just fell continually into the Jupiter environment,
压力一路增强, 增强再增强 and the pressure increased and increased and increased.
它下降时录得的压力是地球的23倍 As it descended, it recorded pressures 23 times greater than on Earth
温度超过300度 and temperatures of over 300 degrees.
深入气态巨行星之中 When you're in the gas-giant environment
你在这氢气浓汤中越沉越深 and you go deeper and deeper into this hydrogen soup
它没有固体表面 that has no solid surface,
却仍有惊人重量 it nevertheless can have a tremendous weight
所以最后仍会把你压毁 And so eventually, you would be crushed
给覆盖物质的重量压毁 by the overlying weight of, of the material that's there.
尽管探测车下坠仅124哩已给压毁 Even though the probe descended for only 124 miles before it was crushed,
仍让科学家匆匆一瞥木星内部面貌 it gave scientists a glimpse of Jupiter's interior.
只是行星的暗黑内心仍然神秘莫测 But the dark heart of the planet still remains a mystery.
跟部分岩质行星一样 Like some rocky planets,
气态巨行星也有磁场 the gas giants have a magnetic field, too.
但它们的磁场不能以常理度之 But these are off the charts.
木星磁场二万倍于地球磁场 Jupiter's magnetic field is 20,000 times more powerful than Earth's
强至延伸到四亿多哩外的土星 and so huge it extends all the way to Saturn, more than 400 million miles away.
一如地球, 木星的磁场挡开太阳风 Like on Earth, the magnetic field deflects the solar wind
保护木星的大气层 and protects Jupiter's atmosphere.
研究木星磁场的科学家 When scientists studied Jupiter's magnetic field,
发现磁场还会影响木星的卫星 they discovered it was affecting Jupiter's moons.
满布火山的卫星艾奥 The volcanic moon, lo,
在相距木星217000哩的地方运转 orbits only 217,000 miles from the planet.
艾奥的火山每秒喷发上吨的气与尘 lo's volcanoes blast a tonne of gas and dust into space every second.
经木星磁场不断增压 And Jupiter's magnetic field supercharges it,
形成强力辐射带 creating powerful belts of radiation.
是以木星附近有不同形式的活动 And that makes the vicinity of Jupiter very active in many different ways.
要是用无线电天线指向木星 If you point a radio antenna at Jupiter,
你可以收听到各种各样的声息 one can hear all sorts of interactions
是行星与磁场之间互为作用的声息 happening between the planets and the magnetic field.
这是木星磁场的声音 This is the sound of Jupiter's magnetic field.
木星与土星不用靠太阳风引发极光 Jupiter and Saturn don't need the solar wind to make auroras.
它们的强大磁场足以自制极光 They have huge magnetic fields that create their own.
钱德拉太空望远镜摄得木星的极光 The Chandra space telescope took these images of Jupiter's auroras.
而太空总署的探测器卡西尼号 And NASA's Cassini probe
则拍下土星极光的美丽影像 took these beautiful pictures of auroras on Saturn.
这些极光证明气态行星也有磁场 These auroras are proof that gas planets have magnetic fields, too.
但气态行星如何产生磁场? But how do gas planets generate magnetic fields?
地球磁场是超热的液态金属… On Earth, a super-hot liquid metal
围绕地球的固态铁核心运转而得来 spinning around the planet's solid-iron core does the job.
气态行星的原理多半大同小异 Gas planets probably do roughly the same thing.
只是气态巨行星并无高热铁质核心 But gas planets don't have hot-iron cores.
它们的核心是尘与冰凝结而成 They formed around frozen cores of dust and ice.
所以核心内的究竟仍然是谜 So exactly what's going on deep inside is a mystery.
木星的最深处究竟由甚么构成 At the very deepest interior of Jupiter,
我们还是莫测高深 we really don't understand what composes those deep interior states.
所以木星中心也许是个实心内核 So it could be that the very centre of Jupiter has a solid core.
又或者真的只有液体 Or it could actually just be still fluid.
我们也许永远不得而知 We may never find out
不会有探测器能走过这44000哩 No probe could ever make the 44,000-mile journey
探索行星的中心 to the planet's centre to investigate.
伽利略号在远离核心处已给压毁 Galileo was crushed before it got anywhere near the planet's core.
于是科学家在地球的实验室里 So now scientists are recreating Jupiter's interior
复制一个木星核心 right here in a lab on Earth.
加州利弗莫尔的国家点燃设施内 Here at the National Ignition Facility in Livermore, California,
他们用最强力的激光模拟木星核心 they're simulating Jupiter's core using the world's most powerful laser.
设施的设计是用来压缩氢气 This facility is really designed to compress hydrogen
压缩至极高密度与温度 to extreme densities and temperatures.
木星内的巨压 Inside Jupiter, extreme pressures are created
来自四万哩厚的氢压向核心的重量 by the weight of 40,000 miles of hydrogen gas crushing down on the core.
在实验室里的方法 In the lab,
则是用192道激光束射向少量的氢 it's done by focusing 192 laser beams on a tiny sample of hydrogen.
待压力达到地球表面压力一百万倍 As the pressure in the sample reaches over a million times the surface pressure on Earth,
氢就会转化为液体 the hydrogen turns into a liquid.
待压力达至地球表面压力几千万倍 But when it reaches tens of millions of times the pressure,
近似木星核心内的程度 more like at Jupiter's core,
氢竟出现奇异变化 something really weird happens to the hycfrogen.
压力大至能促使氢分子重新排列 The pressure is so great that it actually re-arranges the hydrogen,
让基本的氢分子变成可以传导 which is a very basic molecule, until it is able to conduct
于是把42的结构转化为金属形态 So it changes the structure of H2 into a metallic form.
科学家推断木星内也是如此这般 Scientists think this is what's happening inside Jupiter:
压力与热力把内核转化为金属氢 pressure and heat have transformed the planet's core into metallic hydrogen.
木星的金属核心好比地球的铁核心 Jupiter's metallic core works like the iron core in the Earth.
为这颗气态行星产生巨大的磁场 It generates the gas planet's gigantic magnetic field.
引力与热力左右行星的演变路向 Gravity and heat shape how planets evolve,
由内核至外围大气层都受其影响 from their inner cores to their outer atmospheres.
二者是创造行星的创作主力 They're the great creative forces in planet building.
不过还有一种素材能左右行星形貌 But there's another ingredient that has a lot to do with how planets turn out.
那种素材就是水 And that ingredient is water.
then changing
but never stop
我们的太阳系内 In our own solar system,
一颗行星失去大气层后变荒芜废墟 one lost its atmosphere and became a barren wasteland.
另一颗行星则升温而变地狱世界 Another heated up and became the planet from hell
地球也有改变 Planet Earth has changed as well
改变的动力是水 and the game changer was water.
由太空回看地球, 无处不是水 When you look at Earth from space, you see a lot of water.
地球毕竟是个蓝色星球 We are the Blue Planet, after all.
所以一定是湿漉漉的了, 对不对? So it must be really wet, right?
怎看地球表面有3/4给海洋覆盖 It looks at first glance that our Earth of course, covered three-quarters by oceans,
一个水头充足的世界 it's a very water-rich world.
事实不然 Not true.
以质量计, 地球只有0.06%是水 The Earth, by mass, is only 0.06 percent water.
地球表面有水, 就是海洋 There's some water on the surface in the form of oceans,
地幔里也有水 some water trapped in the mantle.
但其实地球是一团干硬岩石 But actually, the Earth is a relatively dry rock.
岩质的内行星全都接近太阳 All of the inner rocky planets formed very close to the sun,
所以诞生之初是干旱之地 so they started off dry.
有水也会蒸发净尽 Any water they might have had evaporated away
或是在撞击时飞走 or was blown away by impacts.
地球诞生时的撞击实在频繁猛烈 These massive collisions that formed the Earth were so energetic
所以这里的水早已蒸发 that any water that had been here would have been vaporised
流出地球 and lost from the Earth,
那么地球今天的水是从何而来? So where did Earth get all the new water we have today?
由外地迁来 It moved here.
你在太空远望 When you look farther out
看看木星、土星、天王星与海王星 and you look at Jupiter, Saturn, Uranus, and Neptune,
那些行星都有大量水分锁在其中 those planets have enormous amounts of water locked up inside them.
更极端的例子是它们的卫星 And even more dramatically are the moons.
木星、土星、天王星与海王星 The moons of Jupiter, Saturn, Uranus, and Neptune
它们的卫星, 成分中过半是水 are at least 50 percent water.
太空之中有许多水 There was a lot of water out there.
太空的水又如何流落地球? So how did some of it get to planet Earth?
十之八九是太阳系更远角落里 And the answer almost certainly is that left farther out in our solar system
哪里的小行星与彗星 were some asteroids and some comets,
它们远离太阳, 得以保留水分 far enough from the sun that they could retain their water.
数以百万计的带水彗星与小行星 Millions of these watery comets and asteroids
飞进内太阳系 came flying into the inner solar system.
部分撞落地球 And some of them smashed into Earth.
千秋万载, 地球接收了小行星的水 Over the aeons, the Earth acquired the water that had been a part of the asteroids,
陆续聚成今天几近覆盖地球的水量 and that indeed makes up the mass of water that nearly covers the Earth today.
至于外来水的多寡 But the amount of water that was delivered?
则全看运气 That was the luck of the draw.
有没有可能… Couldn't it have been the case
当初地球接收的水量少了一半? that the Earth would have acquired, maybe, half as much water as it did?
那地表纵不是完全干涸也差不多 If so, the Earth would be nearly dry on its surface, if not completely dry,
水都给地球核心吸了下去 the sponge of the interior soaking up the rest of the water.
表面没水, 生机免谈 No surface water would have meant no life.
但换了水量过多又如何? And what about too much water?
地球会变成水世界, 深海更深 We would be a water world, the oceans much deeper,
淹没所有大陆, 甚至珠穆朗玛峰 covering the continents, even Mt. Everest.
你不妨问: 假设地球被水覆没 And so you can ask, then, "If the Earth were covered by water,
水量只要比现在多一倍 only having twice as much as it currently has,
那地球还适宜发展科技吗? would we have had a planet that was suitable for technological life?"
科技需要陆地 Technology requires dry land.
所以极有可能… And it's quite likely
是地球刚好拥有的水量 that the precise amount of water that the Earth just happens to have
催生了我们智人这种好科技的人种 has allowed a technological species like we Homo sapiens to spring forth.
我们熟悉的世界之所以存在 The world as we know it exists
乃40亿年前受彗星与小行星的轰炸 because a blizzard of comets and asteroids
给地球带来分量刚好的水 delivered just the right amount of water about four billion years ago.
也许此时此刻, 宇宙间其它角落 And just maybe the same thing is happening right now
正在发生同样情况 somewhere else in the universe.
肯定的一点, 太空里有许多水 One thing's for sure, there is plenty of water out there.
氢是宇宙间最普遍的原子 Hydrogen, the most common atom in the universe,
氧是宇宙间第二普遍的原子 and oxygen, one of the next most common atoms in the universe.
水H2O肯定是最常见的分子 H20 is certainly going to be a very popular molecule.
而我们的宇宙中也确实如此 And indeed it is, within our universe.
宇宙间无处不是水 So water is everywhere in the universe,
我们还发现宇宙间无处不是行星 and we're discovering that planets are, too.
但依然未见第二个有液态水的行星 But we still haven't found another planet with liquid water.
科学家新发现了四百多颗行星 Scientists have discovered more than 400 new planets.
没有一颗与地球面貌相似 None of them look like our world.
始终未找到一颗系外行星… What we have not yet found is a planet that is about the same size and mass
大小、质量与化学成分跟地球相约 and chemical composition as the Earth, orbiting another star.
所以始终是人类的终极追寻 So it remains an extraordinary holy grail for humanity
找一片让我们想起家园的新居地 to find other abodes that remind us of home.
但我们会继续努力 But we'll keep looking.
我们银河系中已有二千亿颗恒星 We know that there are around 200 billion stars in our galaxy alone.
当中四百亿颗有机会有行星 And as many as 40 billion of them could have planets.
我们希望发现类似地球的行星后 We're still hopeful that when we discover terrestrial-style planets
能帮助我们知得更多更深 that will help us tremendously in understanding
穷究我们系内行星与地球的演变 how our own inner solar system planets and the Earth evolved
与系外行星的演变有何异同 in comparison to the outer solar system planets.
我们的行星探索正迈进… We are entering into what is gonna be thought of in the future
将为后世奉为黄金盛世的时代 as the Golden Age of planetary discovery.
我们第一次实实在在了解到… We will really, for the first time, begin to truly understand
太空里果真是千姿百态 the actual diversity that lies out there.
我认为这是一个让人兴奋的盛世 I think it's gonna be a fantastically exciting time.
行星按物理与化学定律诞生 Planets form according to the laws of physics and chemistry.
但往后的变化则要看造化 What they become, that has a lot more to do with luck.
不少科学家相信… Many scientists believe
我们迟早找到一个类似地球的行星 it's only a matter of time before we find another planet like Earth,
它在合适地方以相同材料形成 one that formed from the same ingredients, in the right place,
拥有分量怡好的水 with just the right amount of water.
有一点毋庸置疑 One thing's for sure,
太空里尚有数以十亿计的行星 there are billions of planets out there.
有待发掘 waiting to be discovered.
翻译/摘订时间轴/校对：啥时候摇中