宇宙万物似乎都环绕某些东西运行 In the universe, everything seems to orbit something.
行星环绕恒星、卫星环绕行星 Planets orbit stars and moons orbit planets.
有些卫星有火山活动, 但喷的是冰 Some moons are volcanic, but the volcanoes are ice.
另一些卫星满布大海洋 Others are awash with great oceans.
在我们的银河系 There may be more habitable moons in our galaxy
可住人的卫星或多于可住人的行星 than there are habitable planets.
卫星可解开太阳系一些未知的奥秘 Moons tell the unknown stories of our solar system
让我们明白星系的运作 and show us how it all works.
宇宙有道理 How the Universe Works
第1季第8集：卫星 Moons
我们的太阳系只有8颗行星 In our own solar system, there are just eight planets.
但其中6颗都有卫星环绕运行 But orbiting six of those planets are moons.
很多很多的卫星, 总数超过300 Lots and lots of moons, more than 300 of them.
每一颗各有特色 Each one is different.
每一颗自成一个世界 Each one a world all its own.
我们望出太阳系, 可见到大批行星 Well, when we look out on our solar system, we see a lot of planets.
不过卫星的数目更多 But even more than planets we see moons.
也比它们所环绕的行星 And in many ways, they're more interesting
更有趣味 than the planets that they go around.
有些卫星没有空气, 像月球般死寂 We have moons that are airless and apparently dead, like ours.
但外太阳系有些卫星藏有海洋 Then, out in the outer solar system, we have moons with oceans inside them
有些卫星有大气层 and moons with atmospheres around them.
我喜欢卫星, 行星送给你好了 I'm for moons. You can keep the planets.
太阳系中最灿烂的爆发… The biggest eruptions...
最冷的气温… the coldest temperatures...
最大的海洋 and the largest oceans in the solar system...
都集中在卫星 they're all on moons.
有些卫星满布冰火山 There are moons with ice volcanoes.
有些卫星有甲烷湖、甲烷雨 There are moons with lakes of methane and methane rainfall,
甲烷烟雾、甲烷云 smog, clouds.
有些火山不断爆发, 表面历久常新 Moons that are so volcanically active that they keep remaking their surface.
有些会把各种烟尘, 喷出外层空间 Moons with all kinds of plumes shooting off into space.
环境千变万化, 超乎我们的想象 Really, a much wider range of environments than we ever could have imagined
我向群众以至科学界同事介绍… Often, when I'm describing to general public or even to my fellow scientists,
土星和木星的卫星时 these moons of Saturn and Jupiter,
把它们称为「世界」 I call them worlds.
它们真的是复杂而神秘的世界 Because they really do have the complexity and mystery of a whole world.
木星和土星各有60多颗卫星 Jupiter and Saturn have over 60 moons each.
两颗巨大气体行星和它们的卫星 These giant gas planets and their moons
好像自成一个袖珍太阳系 are like mini solar systems.
而每颗卫星各有不同特色 And each moon has a distinct personality.
土卫八是颗黑白两色的卫星 lapetus, a two-toned moon in black and white.
土卫六有浓密、橙色的大气层 Titan, with a dense orange atmosphere.
冰封的土卫二有冰喷泉 And icy Enceladus blasting ice geysers
喷入太空200英里 200 miles into space.
每颗卫星自成一格 Each moon is unique,
但也有一个共通点: but they all have one thing in common:
它们都是由引力牵制的天然卫星 all moons are natural satellites held in place by gravity.
但卫星不只环绕行星转动 But moons do more than just go around planets,
也发挥稳定作用, 使行星留在轨道 they help stabilise the planets in their orbits
促使太阳系可以畅顺运作 and keep the machinery of the solar system running smoothly.
卫星种类繁多 The diversity of moons
一方面建基于可预计的科学定律 is an interesting combination of predictable laws of science
另方面也是物体相撞后偶然的结果 and then complete randomness of just things smashing together
完全无法预计 and the chips kind of falling where they did in a way that you could never predict.
行星和卫星同出一脉 Planets and moons begin the same way.
恒星诞生后, 大批星尘和气体留下 Once a star turns on, there's a lot of dust and gas left over.
尘埃微粒慢慢集结, 形成岩石 Slowly, the dust particles clump together, forming rocks.
岩石互撞, 形成巨砾 The rocks smash into each other and form boulders.
缓慢地, 物体变得越来越大 Slowly, the objects get bigger and bigger.
这个过程名为「吸积」 The process is called accretion.
就像雪球滚下山坡 One can think of it as forming a snowball and rolling it down a hill.
滚下山之际 As it, as it rolls down the hill,
积聚的雪越来越多 it collects and gathers up yet more snow
雪球越滚越快, 力度越来越强 which makes it roll faster and harder.
这种不受控的吸积现象 And, and so that process of runaway accretion
在行星的形成过程中出现 actually happens in the formation of the planets...
卫星也是如此形成 and in the formation of moons as well.
听起来很简单 It sounds simple enough,
但之前无人肯定 but nobody knew for sure how it worked...
直至2003年 until 2003.
在国际太空站上 On the International Space Station,
航天员唐佩蒂特进行零引力实验 astronaut Don Pettit was experimenting in zero gravity.
他把盐和糖放入塑料袋内 He put grains of salt and sugar inside a plastic baggie.
它们没有散开, 反而凝集起来 Instead of floating apart, they began to clump together.
行星和卫星正是如此形成 This is how both planets and moons build up.
但它们不是围绕恒星 But instead of taking shape around stars,
大部分卫星是围绕行星而成形 most big moons take shape around planets.
既然是由同一过程产生 If the same process makes them all,
因何又有不同特性? what makes all of them so different from each other?
以木卫四和木卫三为例 Take two of Jipiter's moons, Callisto and Ganymede.
两颗截然不同的木星卫星 Two very different moons,
都在木星年轻时 each born from the same debris
从同一堆星尘产生 when Jupiter was still young.
木卫三靠近木星, 周围有大量星尘 Ganymede formed close to Jupiter where there was lots of debris.
因为有这么多材料可用 Because there was so much material,
所以在一万年之间, 迅速成型 it came together quickly at about 10,000 years.
而且很热 And it was hot.
热力把冰和岩石分开 The heat separated the ice from the rock.
现在仍可从木卫三独特的地形见到 You can still see it in Ganymede's distinct landscape.
能量是主宰卫星形状的要素 The primary factor that affects why moons are the way they are today is energy;
要看吸积过程中, 得到多少能量 how much energy was put into them as heat during accretion...
之后又失去多少能量 and how much energy has been lost.
这些因素可解构卫星今日的行为 All of those factors go into telling us why moons behave the way they do
也说明了它们因何有现今的形状 and why the look the way they do today.
木卫四的表面显示另一情况 Callisto's surface tells a different story.
它在较远处形成, 星尘和热力较少 It formed much farther out where there was less debris and less heat
形成时间较长, 冷却程度较快 It took longer and cooled faster.
木卫四的表面比木卫三更统一 Unlike Ganymede, Callisto's surface is uniform:
岩石和冰从来未曾分开过 rock and ice never separated.
成形的位置也主宰卫星的生死 Where a moon forms can also mean the difference between survival and destruction.
太靠近行星, 会被引力摧毁 Get too close, and the planet's gravity will rip a moon to shreds.
科学家相信木星年轻时 Scientists believe this is what happened
有不少卫星因此死亡 to many moons when Jupiter was young.
木星很可能曾有一批大的卫星 And it's very likely that Jupiter had an entire conveyer belt of large moons
不过它们都被木星吞噬了 that when they formed only to be swallowed up by the planet itself.
今天所见的戴维星是硕果仅存 The large moons we see today are only the last ones
它们稳定下来, 不再转入死路 that were able to stabilise right at the end of that process,
于是得以存活, 并留在今天的位置 stop their death spiral, and survive into the position we see today.
但木星仍不断想把它们吃掉 But Jupiter keeps trying to eat them.
巨行星的引力不断拉扯周围的卫星 The gravity of the giant planets reaches out and pulls hard on the orbiting moons.
把一些没有生命的岩体 It transforms them from lifeless balls of rock...
变成奇异、变化多端的世界 into strange and dramatic worlds.
在我们的太阳系, 木星是最大行星 Jupiter is the largest planet in our solar system.
有63颗卫星 It has 63 moons.
最大的4颗定名为「伽利略卫星」 The four largest are called the Galilean moons,
纪念伽利略于1610年发现它们 named after the astronomer Galileo who discovered them in 1610.
它们显示, 引力主宰卫星的形状 They show how gravity controls both what moons look like
以及特性 and how they behave.
第一颗「伽利略卫星」是木卫一 The first of the Galilean moons, lo,
它的轨道最接近木星 orbits closest to the planet,
就在木星26万英里之上 just 260,000 miles above Jupiter.
大约相等于月球和地球的距离 That's about the same distance as our moon is from Earth.
但木卫一不同月球, 没有撞击坑 But unlike our moon, the surface of lo has no impact craters.
这显示, 卫星表面是新形成的 Scientists realised that meant the surface was new,
但怎么可能呢? but how could that be?
每次从宇宙飞船 Every time you look at Io with a spacecraft
或望远镜望向木卫一 or even with a telescope,
总发觉它有少许不同 it, it, it's a little bit different.
木卫一的地质, 像行星天气的多变 So the geology on lo changes like the weather on other planets.
真的很活跃 It's that active.
太空总署初次探索木卫一时 When NASA first sent probes to fly past lo, they were shocked
见到数十座活火山, 大吃一惊 They saw dozens of active volcanoes.
这是木卫一超级火山爆发的片段 This is footage of an erupting super volcano on lo,
直喷到太空200英里 blasting 200 miles into space.
人人都发出同一疑问: Everyone had the same question:
卫星怎可能有活火山? How could there be active volcanoes on a moon?
答案很简单: 引力 The answer was simple: gravity.
木星引力强大, 可以把卫星挤压 Jupiter's gravity is so huge that it reaches out and crunches the moon.
而且不只是木星的引力拉扯木卫一 And it's not just Jupiter's gravity pulling on lo.
其它卫星经过时, 也把它拉动 Other nearby moons also pull on it as they pass by.
于是木卫一的核心不断被拉来拉去 So the core of the moon is being worked back and forth all the time.
这叫「潮汐摩擦」 It's called tidal friction
在木卫一核心产生极大热力 and it generates extreme heat on lo's core.
好像把铁衣架扭曲, 直至折断一样 Almost like bending a wire coat hanger until it breaks
可以感觉到衣架内的热力 and you feel the inside of the coat hanger there, it feels rather warm.
潮汐摩擦力使木卫一内部发热 That tidal friction, that internal friction heats the interior of lo
变成太阳系中 until it's become actually
最活跃的火山地带之一 one of the most volcanically active worlds in the solar system.
不停的拉扯 The constant pushing and pulling
使木卫一内部温度高达数千度 generates temperatures thousands of degrees high inside lo.
于是喷出大量的熔岩 It blasts out in gigantic eruptions of lava.
木卫一是太阳系中 lo is the prime example of tidal forces
潮汐摩擦和引力互动的 and gravitational interactions
最佳例证 in the solar system.
它被木星不停的拉扯 It is constantly being pulled by Jupiter
也被其它卫星不停的拉扯 and it's constantly getting pulled by the other moons as well.
于是产生大量热力 And so as a result, there's a tremendous amount of heat created.
熔岩不断喷出, 重铺木卫一的表面 The floods of erupting lava constantly resurface lo,
所以卫星上见不到撞击坑 which is why there are no visible impact craters on this moon.
引力亦使附近的木卫二发热 Gravity also heats lo's neighbour, Europa.
木卫二距离木星较远 Europa's orbit is farther away from Jupiter
所以冷得多 so it's much colder.
木卫二不喷熔岩, 它的表面是冰层 Instead of lava, the surface of Europa is ice.
南极洲最低温纪录是零下128度 The lowest recorded temperature in Antarctica is minus 128 degrees.
木卫二表面的温度更低一倍 Europa's surface is twice as cold.
但在冰层之下, 可能有水 But underneath all the ice, there may be an ocean of water,
因同一潮汐摩擦作用而发热 heated by the same tidal friction that makes lo volcanic.
木卫二几乎可以定有地下海洋 Europa has a subsurface ocean almost certainly.
地表下海洋和岩石地幔相接 And that subsurface ocean is in contact with the rocky mantle,
因此产生热力 which provides heat,
也可能产生养份, 支持生命 and also provides, probably, appropriate nutrients to sustain life.
将来我们会探索木卫二冰层下状况 Someday we'll send a probe to explore beneath the ice on Europa.
说不定会在温暖海洋内发现生物 And maybe we'll discover life forms living there in warm Europan oceans.
在木卫一和木卫二之外 Out beyond lo and Europa
有接近60颗卫星 are nearly 60 more moons.
它们在远离木星的轨道上运行 They orbit much further away from Jupiter
木星引力的效应比较弱 where the affects of the giant planet's gravity are much weaker.
无法产生潮汐摩擦, 使卫星发热 Out here, it's too weak to generate tidal friction and heat the moons.
所以这些遥远的世界寒冷而荒芜 So these remote worlds are cold and barren.
但也不是平淡无奇 But not featureless.
它们有无数次撞击后留下的疤痕 They bear the scars of countless collisions,
科学家相信 and scientists believe
最奇妙的卫星系统因撞击而形成 it was collisions that created the most extraordinary moon system of them all.
土星拥有最不寻常的卫星系统 The planet with the most unusual moon system is Saturn.
范围覆盖20万英里以上 It's spread out over more than 200,000 miles.
严格来说, 它有超过十亿颗卫星 Technically, there are more than a billion moons.
不错, 是十亿颗卫星 That's right, a billion moons.
它们集结起来, 组成土星环 And all together, they make up Saturn's rings.
卫星可以是小如卵石的岩石或冰块 A moon can be a hunk of rock or ice no bigger than a pebble
只要是围绕行星运行便合格 as long as it orbits a planet.
土星环由无数的岩石和冰块组成 The rings of Saturn are made of countless pieces of rock and ice.
体积由卵石以至整座城市不等 They go from the size of a pebble up to the size of a city.
土星环上有些颗粒 We don't refer to all the ring particles...
宽度10至20米 that can get to be as big as 10 to 20 metres across,
我们并不称为卫星 we don't refer to them as individual moons,
但如果宽度达1至2公里 but when we find a body that is maybe a kilometre or two across,
便可以开始称为卫星或小卫星 then you can start talking about it as a moon or a moonlet.
土星环是最悠久的天文奥秘之一 Saturn's rings are one of the oldest mysteries of astronomy.
它们从何而来? Where did they come from?
为寻求答案 To try and find out,
太空总署派出卡西尼号探测器 NASA sent the Cassini probe
执行为期12年的任务 on a 12-year mission
研究土星、土星环和卫星 to study Saturn, its rings, and its moons.
卡西尼号拍回了一幅最美丽的图片 We took with Cassini probably the most beautiful picture that's ever beer taken,
不只我一个人这么说 and I'm not the only one who has said this.
卡西尼被土星在太阳下的阴影盖着 Cassini was in the shadow of Saturn cast by the sun.
所以见不到太阳 And so you don't see the sun,
见到背光的土星和美丽的光环 you see the backlit planet of Saturn and its beautiful rings.
见到从土星边缘折射出来的阳光 You see the refracted image of the sun poking out from the side of Saturn
在这美景当中, 有一颗小圆点 and nestled in all of that splendour is this small little dot
那颗小圆点不是卫星 That tiny dot is not a moon.
那是接近十亿英里外的地球 That is the distant planet Earth nearly a billion miles away.
我们对土星、土星环和卫星的认识 Most of what we know about Saturn, of its rings and moons,
大部分来自卡西尼号 comes from Cassini.
之前我们以为只有8个环 Before Cassini, we thought there were only eight rings.
今天见到30个以上 Today, we can see over 30.
土星哪里景物丰盛, 令人眼花缭乱 And what we have found at Saturn has been just literally an embarrassment of riches.
这是以前见过的东西 We're seeing something that we had seen before,
但现在见到的细节和清晰程度 but now we're seeing it with a level of detail and clarity
令人瞠目结舌 that was just mind-blowing.
从前以为是土星约40亿年前形成后 Scientists used to think the rings were made of the icy leftovers
剩下的冰粒子形成这些环 after Saturn was formed about four billion years ago.
但历史这么悠久的物体 But anything that old should be covered
理应布满星尘和污垢 with cosmic dust and dirty.
因何土星环外表光洁如新? So why does Saturn's rings appear bright and clean, almost new?
指挥中心把卡西尼号移近土星环 To get the answer, mission control manoeuvred Cassini close to the rings.
探测器发现 The probe saw that
环上冰块不停地撞击和破裂 all the ice pieces in the rings are constantly colliding and breaking up.
每次撞击后都露出一些光洁的表面 And each collision exposes new surfaces that are clean and polished.
以下是天文学家的推论 This is what astronomers think happened.
土星年轻时没有环, 只有大批卫星 When Saturn was young, it had no rings, just lots of moons.
在某一刻, 有颗冰冷彗星不速而至 At some point, an icy comet zoomed in from deep space
撞向其中一颗卫星 and smashed into one of those moons.
彗星分裂成数十亿碎片 The comet broke up into billions of pieces.
撞击力亦把卫星推近土星 The impact also pushed the moon closer to Saturn
土星的强大引力令卫星解体 where the planet's enormous gravity broke it up.
卫星的碎砾和彗星的冰混合起来 Now debris from the moon and ice from the comet mixed.
在引力拉动下, 逐渐形成环状 Gradually, Saturn's gravity pulled all those fragments into rings around it.
卫星全靠引力造就 The story of moons is the story of gravity.
引力把它们固定在轨道上 Gravity holds them in orbit.
使卫星核心发热、造成不同的表面 It heats up their insides and shapes their surfaces.
主宰卫星的一切, 甚至生死存亡 In the end, it controls everything about moons, even their survival and destruction.
引力更可以掳劫小行星、彗星 Gravity can even create new moons
以至整颗行星, 把它们变成新卫星 by kidnapping asteroids, comets, and even whole planets.
我们知道, 引力可以创造卫星 We know that gravity makes moons.
标准的办法是集结… The standard way is to assemble them
行星诞生时留下的星尘去砌成 from debris leftover when planets are formed.
但另一个办法是: 俘掳它们 But gravity makes moons a second way, too: it captures them.
试想像一颗彗星或小行星 Imagine a wandering comet or asteroid, somehow it gets knocked off course.
被撞离轨道, 靠近某颗行星 It wanders too close to a planet
引力像科幻小说中的牵引波束 Gravity acts like a science fiction
把它抓住 tractor beam and grabs it.
如果引力不够强, 它便可逃脱 Not quite enough gravity, and it escapes.
如果引力太强, 它便撞向行星 Too much gravity, and it collides with the planet
引力怡到好处, 它便环绕行星运转 Just enough, and the comet or asteroid goes into orbit around the planet
成为新卫星 and becomes a new moon.
火星有两颗小卫星 Mars has two tiny moons
定名为火卫一和火卫二 named Phobos and Deimos,
都是被俘掳的小行星 both are captured asteroids.
一颗在环绕行星时不断向外推 One is pushing outward as it circles the planet
终有一天会脱离, 继续遨游外层空间 and will eventually break free and continue on its journey through space.
另一颗不断向内转向火星 The other is circling inwards, a little closer to Mars all the time.
终有一天会相撞 Eventually, it will smash into it
？？？ This is prove with me.
只是颗3英里宽的小行星 it's an asteroid, really, just three miles across.
但有时被称为地球的第二颗卫星 But it's sometimes described as Earth's second moon.
1986年发现了小小的克鲁特尼之后 With the little object Cruithne, which was discovered back in 1986,
我们开始研究 we start to get into this realm
卫星的定义 of, of what does it mean to be a moon.
不过数千年之前 Only a few thousand years ago,
克鲁特尼是颗普通的小行星 Cruithne was an ordinary asteroid
像数十亿同类, 环绕太阳运行 orbiting the sun like billions of others,
但后来它脱离了小行星带的轨道 but eventually, it wobbled out of its orbit in the asteroid belt
被地球的引力吸去 and got snagged by Earth's gravity.
但克鲁特尼的举动很不寻常 But then Cruithne did something unusual.
它不像正常的卫星那样环绕地球 Instead of orbiting around the Earth like a normal moon,
而是跟在地球后面 Cruithne began to follow behind it
所以我们可把它当成地球的卫星 And so one might call this sort of a moon of the Earth,
但又不是完全贴切 not exactly, though, because that object is designed,
因为它是环绕太阳, 不是地球 you know, it's on its own independent orbit around the sun, not the Earth.
有时小行星也俘掳卫星 Sometimes asteroids capture their own moons.
1993年, 伽利略宇宙飞船 In 1993, the Galileo spacecraft
飞过小行星埃达 flew past the asteroid Ida
有出人意表的发现: and found something nobody expected:
一颗细小、宽半英里的卫星 a tiny, half-mile wide moon.
这只是宇宙飞船经过的第二颗小行星 The fact that we saw a satellite around only the second asteroid
便发现它有颗卫星 ever to be encountered with a spacecraft
显然, 小行星有卫星是寻常现象 immediately tells us that moons around asteroids must be incredibly common.
被俘掳的卫星不一定细小 Not all captured moons are small.
最大的被俘掳卫星是海卫一 The mother of all captured moons is Triton.
它环绕海王星运行, 十分巨大 It orbits the planet Neptune and it is big,
直径大约1,700英里 about 1,700 miles in diameter.
但海卫一是颗不寻常的卫星 But Triton is a moon with an unusual story.
海卫一令行星学家感到大惑不解 Triton was a very puzzling problem for planetary scientists
因为传统观点是… because our traditional views would tend to make all the moons orbit
卫星跟着行星的方向转动 in the same direction of the planet itself spins.
海卫一环绕海王星的方式却不同 In the case of Triton around Neptune, it's the other way around.
海王星向这边转动 Neptune is spinning this way,
海卫一向相反方向运行 Triton is orbiting around in the opposite direction.
这显示它不像大部分卫星… This means it didn't form like most moons
从行星诞生时留下的星尘形成 out of the debris left over from the birth of the planet
否则它应该转往同一方向 or it would orbit in the same direction.
所以有些反常 So something wasn't right.
海卫一很巨大、轨道奇特、很反常 Triton is huge, and its orbit is funny. it's anomalous.
不似是和海王星同出一系 It does not seem as though it formed as a part of the Neptune system.
比较像是颗被俘掳的行星 It seems much more like a captured planet.
科学家现时相信海卫一曾是矮行星 Scientists now think Triton was once a dwarf planet
像冥王星一样 like Pluto.
以海王星这么巨大的行星 And a giant planet like Neptune certainly has enough gravity
它的引力当然足以俘掳海卫一 to capture a moon the size of Triton.
海卫一几可肯定在外太阳系形成 Triton was almost certainly formed way out in the outer solar system,
然后被海王星俘掳 and then at some point was captured by Neptune.
海卫一可能曾经拥有一颗卫星 Perhaps Triton early on had its own moon.
两颗星同时被俘掳 They both were captured,
卫星在俘掳过程中毁灭 and then that moon was destroyed during the capture process.
但海卫一也有危险 But Triton is in danger,
海王星正把它越拉越近 Neptune is dragging it closer and closer.
终有一天, 距离太贴近 Eventually, it will get too close...
便会被海王星强大的引力摧毁 and Neptune's immense gravity will tear it apart.
海卫一便会变成行星周围的环状体 Triton, the moon, will be reborn as a ring system around the planet.
但我们的卫星月球呢? But what about our moon?
它从何而来? 是否被俘掳呢? How did it get there? Was it captured?
事实比想象中更加离奇 The truth is even more extraordinary.
它是在极端狂暴的环境中诞生 It was born in extreme violence.
月球像大部分卫星一样 Our moon, like a lot of moons, is rocky,
布满岩石、荒芜、有很多撞击坑 barren and pockmarked with craters.
但在某一方面, 却又与别不同 But in one way, our moon is unique in the solar system.
长久以来, 天文学者都以为 For a long time, astronomers thought
月球由地球诞生后留下的星尘形成 the moon formed from debris left over from the birth of the Earth.
但1960年代的研究员提出不同见解 But researchers in the 1960's came up with a radically different idea.
他们认为是强大撞击的结果 They suggested it came from a giant impact
初次提出月球 When we first had the idea
因撞击而形成时 of forming the moon from a giant impact,
并不受大众欢迎 that was not a terribly popular idea.
有些科学界好朋友和同事对我说: And I actually did have good science friends, colleagues, coming to me, saying,
应该先详尽考虑各种缓慢进化理论 "You know, we really have to exhaust all the, the slow evolutionary theories
然后才谈大灾难也不晚 before we start talking about cataclysms."
比尔夏文需要的证据在月球上 The evidence Bill Hartman needed was on the moon itself.
等到1969年太阳神登月才找到 And the proof had to wait until Apollo astronauts finally went there in 1969.
他们把数以百磅的月球石带回来 They brought back hundreds of pounds of moon rocks.
科学家分析岩石后, 啧啧称奇 Scientists analysed the rocks and were amazed.
岩石和地球的地壳一模一样 They were identical to rocks in the Earth's crust...
而且热力强大 and they'd been superheated.
地球的地壳怎会变热和跑上月球? So how did pieces of the Earths crust become super hot and wind up on the moon?
夏文自认可以解答 Hartman was pretty sure he knew.
地球形成时, 有东西撞击它 This whole idea was that the Earth forms, now you hit it with something,
把上面轻巧的岩石吹走 you blow all this light rocky material off the top,
它们便环绕地球运行, 成为卫星 that material goes into orbit and makes the moon.
卫星由岩石碎砾形成 The moon's just made out of rocky debris.
试想像45亿年前太阳系的混沌情况 Imagine our chaotic solar system four and a half billion years ago.
年轻的地球是一百多颗新行星之一 The young Earth is just one of a hundred or so new planets orbiting the sun.
有颗行星叫忒伊亚, 像火星一样大 One of them is a Mars-sized planet called Theia,
和地球处于碰撞轨道 and it's on a collision course with Earth.
结果以数千英里时速相撞 They smash into each other at many thousands of miles an hour.
忒伊亚被毁灭, 地球一息尚存 Theia is destroyed, and Earth barely survives.
撞击力把数十亿公吨星尘射入太空 The impact blasts billions of tonnes of debris into space.
地球的引力把它们拉入轨道 The Earth's gravity pulls it into orbit around the planet.
于是地球的碎屑集结, 形成月球 Now these hunks of leftover Earth clump together and form our moon.
这是科学理论, 但如何测试? That's the theory, anyway. But how do you test it for real?
在太空总署的虚拟射击场 Here at NASA's vertical gun range,
科学家重组这场远古的撞击事件 they're recreating that ancient collision in a lab.
这座30英尺长的大炮 This 30-foot long gun fires
以18,000英里时速发射一颗小弹丸 a tiny projectile at 18,000 miles an hour.
这颗弹丸代表忒伊亚 The projectile is Theia.
这个球体代表地球 This ball represents the Earth.
只要改变忒伊亚的撞击角度 By changing the angle of Theia's impact,
便可以计算出到底需要多大撞击力 the team can figure out how precise the ancient collision had to be...
才创造出月球 in order to make the moon.
第一次发射, 只在地球表面擦过 In the first shot, Theia hits the top of the Earth with a glancing blow.
这是浮游在太空中的地球 So here's the Earth, if you will, just suspended in space.
它受到撞击 And now it's gotten hit
地球喷出一些物体 So now we see the planet, the ejecta is being ripped out of the Earth
形成巨大的撞击盆地 and is forming this giant impact basin.
如果真的在地球发生 And if this really were the Earth,
盆地宽度达数千公里…数千英里 this basin would be thousands of kilometres, thousands of miles across.
在这次模拟实验, 只撞出少许地表 In this simulation, Theia only skims off the surface of the planet...
射出少量星尘出太空 and very little debris is thrown out into space.
不足以形成月球 Not nearly enough to build our moon.
第二次发射是迎头撞击 The second shot is a head-on collision.
呯, 地球就此消失 Ka-pow, that's the end of planet Earth, it's gone.
部分星尘会飞出太阳系以外 Some of the debris is gonna go out of the solar system,
部分星尘会重新吸积 some of the debris will re-accrete
形成太阳系内一些小小星子 to form small planetesimals within the solar system.
地球不再存在 There's no Earth left,
没有引力可收集星尘, 去形成月球 so there's no gravity to gather the debris and form the moon.
现在大炮校准在适当角度 Now the gun is set to just the right angle,
在轻轻擦过和直接撞击之间 halfway between a glancing blow and a direct hit.
看看地球勉强存活下来的结果 So we'll see what happens if the Earth barely survives.
噢, 美妙! 哗, 厉害! Oh, oh, gorgeous! Oh, my gosh, ka-pow!
现在有整片地壳给炸掉 Now we have the entire part of the Earth being ripped apart,
但喷出的烟雾…厉害! but the vapour plume is...Oh, my gosh!
太好了 Jeez! That is gorgeous.
这就是月球的起源 But this was the beginning, the beginning of our moon.
实验证明忒伊亚可能撞向地球 The experiment shows that Theia could have smashed into the Earth
于是创造了月球 and formed the moon.
不过撞击力必须恰到好处 But the collision had to be just right.
幸好也确实如此 And lucky for us, it was.
今天, 月球在地球25万英里外运行 Today, the moon orbits 250,000 miles from Earth.
但月球初诞生时 But when it first formed,
只在地球15,000英里之外运行 the moon orbited just 15,000 miles above the Earth's surface.
月球形成后5亿年 500 million years after the moon formed,
如果我们抬头仰望 if we looked up, in the sky,
会见到月球雄据大部分天空 the moon would have comprised a tremendous portion of the sky,
因为月球很贴近地球 it would have been enormous
所以看起来巨大无比 because the moon would have been much closer.
当时地球转得快, 一天只有6小时 Back then, the Earth was rotating so fast, a day lasted just six hours.
但月球近在眼前, 引力有煞停作用 But the moon was so close, its gravity acted like a brake.
直至一天变成24小时 until a day now lasts 24 hours.
月球引力亦导致地球潮水暴涨 The moon's gravity also created giant tides that surged across the planet
海水翻腾, 矿物质和养份混合起来 churning up the seas, mixing minerals and nutrients.
形成原生浆液, 生命由此诞生 This created the primordial soup from which the first forms of life arose.
没有月球, 地球可能永远没有生命 Without our moon, life on Earth may never have happened.
其它卫星亦可能和生命有关连 And there may be other moons with a link to life as well.
卫星可能是宇宙的伟大生物实验 Moons may be the great biology experiments of the universe,
生命的真正实验室 the true laboratories of life itself.
卫星充满惊喜 Moons are full of surprises.
有些卫星有大火山 There are moons with giant volcanoes,
有些卫星有大海, 藏在厚厚冰层下 moons with vast oceans sealed under thick ice.
现在又知道有一些布满有机复合物 And now we know a few are rich in organic compounds.
如果配合得宜, 甚至可能长出生物 In the right combination, they might even support life.
在我们的太阳系 In our solar system,
想了解宇宙其它地方的奥秘 the biological window through which we can understand the rest of the universe
或者要透过外太阳系的卫星去研究 may be through these moons of the outer solar system.
可能从中找到第二部创世记 That may be where we find our second genesis,
第二部创世记让我们真正明白 and that second genesis is really our first deep understanding
宇宙的生物本质 of the biological nature of the universe.
乍看起来, 卫星不似适宜生物居住 At first glance, moons don't look ideal for life.
例如土卫二 Take Enceladus.
它是个宽300英里的闪亮冰球 It's a shiny ball of ice, 300 miles across,
环绕土星运行 orbiting Saturn.
它是太阳系中最光亮的物体 It's the brightest object in the solar system.
射来的光都百分百给它反射出去 It reflects a hundred percent of the light that hits it
因为表面是水冰, 所以亮度超高 So it's super bright, and that's because it's water ice.
2005年卡西尼号发现… In 2005, the Cassini probe spotted ice volcanoes
土卫二的冰火山爆发 erupting from the surface on Enceladus.
显示冰下一定有热力 That meant there had to be heat under all that ice,
热力产生大量的水 heat that created oceans of water.
而有水的地方就可能有生命 And where there's water, there's the possibility of life.
这是黄石公园的蜂窝间歇泉 So this is Beehive Geyser here in Yellowstone,
把水蒸气和水射上约150英尺高空 and it is shooting water vapour and water about 150 feet into the sky.
相当壮观 And it's pretty incredible.
现在请想象自己站在土卫二之上 So now imagine if you're on the surface of Enceladus,
你会见到类似的间歇泉 you would see geysers that look a lot like this...
把冰粒和水蒸气喷入太空 and they are shooting ice grains and water vapour into space,
比这个间歇泉高出数千倍 thousands of times higher than this geyser here.
冰火山的动力来自引力 The ice volcanoes are powered by gravity.
运作原理如下 Here's how it works.
土星的引力使卫星核心发热 Saturn's gravity works on the core of the moon, heating it up.
地底的水膨胀 The underground water expands
逼上表面冰层的隙缝 and forces its way up through cracks in the surface ice
以冰晶形态射入太空 and blasts out into space as ice crystals.
造就了太阳系中最壮观的大爆发 These are some of the most spectacular eruptions in our solar system.
相形之下, 蜂窝间歇泉像一支水枪 They make Beehive Geyser look like a squirt gun.
科学家从火山的冰… From the ice in the volcanoes,
找到盐和简单的有机复合物 scientists have detected salt and simple organic compounds.
显示冰下的水既温暖, 又富有养份 That means the water under the ice is not only warm but full of nutrients.
是否很熟悉? Sound familiar?
热力、水和养份 Heat, water and nutrients,
地球生命就是由此诞生 that's how life on Earth began.
原来地球海洋有的一切 We realise you could have all the things that we associate with oceans on the Earth
都存在于卫星 going on inside a moon.
真是个难得的大发现 It's the discovery of a lifetime.
土星的土卫二有海洋 Saturn's Enceladus has an ocean,
木星的木卫二也有 so does Jupiter's Europa.
但不只它们可能长出生命 But these aren't the only moons where life could emerge.
土星有另一颗卫星 Saturn has another moon,
土卫六长出生命的潜力更大 Titan, with an even greater potential for life.
2005年卡西尼号派出惠更斯号 In 2005, Cassini sent a probe called Huygens
往土卫六执行一个单程式任务 on a one-way mission to Titan.
全程历时仅3.5小时 For just three and a half hours,
惠更斯号从接近十亿英里外的星球 Huygens transmitted live pictures from the hostile surface...
实地传来图片 nearly a billion miles away.
然后电池便用罄 Then the battery died.
真的了不起 It was just incredible.
人类透过自己发明的工具 This was the first time humans had ever touched this moon
首次触摸这颗卫星 with something of our own making.
是值得全球庆祝的大事 It was just an event that should have been celebrated the world over.
我们应该在欧美各大城市 We should have had ticker-tape parades
举办巡游 in every major city across the US and Europe
作为庆祝 to celebrate this.
这是开创先河、值得惊叹的大事 It was that history-making and that astonishing.
土卫六的雨点是地球的两倍 Raindrops on Titan are twice as big as raindrops on Earth.
但雨点不是水, 而是甲烷 But the rain isn't water, it's methane.
在地球, 甲烷是气体 On Earth, methane is a gas,
但因为土卫六很冷, 甲烷呈液态 but on Titan, it's a liquid because the moon is so cold.
可能有甲烷冰山 There may be methane icebergs,
肯定有甲烷湖和河 there's certainly methane lakes and rivers
有甲烷雨和甲烷云 and there's methane rain and methane clouds,
可能有昆虫浮游于甲烷内 and maybe bugs swimming in methane.
昆虫活在液态甲烷, 似是天方夜谭 Bugs living in liquid methane may sound unbelievable.
但科学家发现… But scientists have discovered
土卫二、木卫二和土卫六 that Enceladus, Europa and Titan
都有种名为托林的物质 are all covered with a substance called tholin.
托林含有生命必需的化学材料 Tholin contains the chemical building blocks for life to begin.
那么这些卫星是否有机会有生命? So could life emerge on any or all of these moons?
我们无法从卫星取得托林 We can't get our hands on the tholin from the moons,
所以基思麦卡在实验室仿制 so Chris McKay makes it in the lab.
他电击从土卫六发现的混合气体 He zaps a mixture of gasses found on Titan with electricity.
得到的结果是一堆红褐色泥土 What he gets is a reddish brown mud.
这就是我们要造的托林 So this is what we make, tholin,
是种非生物有机物质 this sort of non-biological organic material.
当化学能量进入简单分子 It's produced by chemical energy put into simple molecules
例如甲烷和氮, 便产生这种物质 like methane and nitrogen, and here we got it
这就是在土卫六见到的物质 And that's the material we see on Titan.
我们在土卫二也见到类似的证据 We see evidence for something like this on Enceladus.
外太阳系不少卫星的表面也有 We see it on the surface of many of the moons in the outer solar system.
这是大自然孕育生命的原料 This is nature's recipe for making the stuff that life eventually emerges from.
在太阳系外围某个遥远的卫星上 Somewhere in the outer reaches of our solar system, on some remote moon,
可能已经孕育出生命 life may have already emerged.
但可能不是我们所认识的生命形体 But it probably won't be life as we know it.
2.0版本不一定有1.0版本的基因 Life 2.0 doesn't necessarily have to have the same genetics as life 1.0, right?
事实上, 差异越大, 趣味越大 In fact, the more different it is, the more interesting it is.
无论是相同或有异 Whether it's the same or very different,
如果在太阳系的卫星找到生命 the discovery of life on the moons of our solar system
都会改变我们对宇宙的看法 will change the way we look at the universe.
如果发现生命不只出现过一次 I think that should we ever find that life had originated
而是在太阳系出现了两次 not once but twice in our solar system,
那么你很轻易地驳斥… then you, you, you can easily dismiss any arguments
只有地球有生命这个说法 that say that life is unique to the Earth.
卫星虽小, 却是变化多端的世界 Moons are small, but they're still diverse and dynamic worlds.
帮助我们了解宇宙的运作 They help us understand how the universe works.
它们是宇宙必需的齿轮 They're essential cogs in the cosmic machine.
没有了卫星 Without any moons,
我们的太阳系 our solar system
便会面目全非 would be a very different place.
没有月球 Without our moon,
地球可能没有生命 life may never have evolved on Earth.
有谁知道 Arid who knows?
下次在宇宙某处 When and if we find new life
找到新生命时 somewhere else in the universe,
可能不是另一颗行星 its home may not be another planet at all.
而是一颗卫星 It might be a moon.
翻译/摘订时间轴/校对：啥时候摇中