美国国家航空航天局“信使”号水星探测器发射升空 Lift off of Messenger on Nasa's mission to Mercury.
水 星
金 星
火 星
木 星
土 星
天 王 星
海 王 星
行星 第4集
在温暖的内太阳系之外 Beyond the warm worlds of the inner Solar System...
在气态巨型星木星之外 beyond the gas giant Jupiter...
在远离太阳的寒冷空间里 in the freezing regions far beyond the Sun...
土星运行其中 lies Saturn...
这颗行星因拥有近30万公里宽的固态冰质行星环 a planet made unique, thanks to a nearly 300,000km-wide ring
而显得极为独特 of frozen water.
这里的数万亿块冰在引力的作用下 Here, trillions of pieces of ice have been sculpted by gravitational
被塑造成了太阳系中最令人赞叹的奇观之一 forces into some of the Solar System's most stunning vistas.
地球上的水有多种形态 海洋 云雾 Here on Earth, water takes many forms - oceans and clouds
和河流 而结晶态的冰 and rivers, but it's in its crystalline form, ice,
却是最美丽的一种 that it's at its most beautiful.
这里的冰成为地球上的一道景色 但在土星所处的太阳系外层 Here, ice just adorns the landscape, but in the Outer Solar System,
冰的储量极为丰富 where Saturn lives, ice is so abundant that, well,
以至于成为了基础的构造材料 it's become a building material.
在太阳系中没有比土星的冰环 Now, there's no more beautiful sight in the Solar System than
更美丽的景象了 the ice rings of Saturn.
它就像是上帝把雪片轻轻撒在了引力场上 It's almost as if a god had taken snowflakes and sprinkled them
让我们观赏 但如此精致的景象 over a gravitational field, so we could see it, but how could
怎么会是如此简单的事物创造的呢 something so intricate be sculpted out of something so simple?
其实 科学一贯都是如此 Well, as is always the case in science,
现象中蕴含着真理之美 the true beauty lies in the story.
土星是太阳系中一颗经历过 Saturn is a planet that has undergone some of the most
剧烈转变的行星 radical transformations in the Solar System.
它经历过毁灭 A planet that has seen destruction...
经历过创世 and creation.
这颗行星上存在众多隐秘的世界 A planet that harbours hidden worlds...
那里或许 where, just perhaps,
可能存在着生命的 there may exist a second home
第二个家园 for life.
太阳系远端的生命 土星
设想一下 一颗表面无处立足的星球 Imagine a place with no surface to stand.
那里只有无尽的气体 Just an endless atmosphere.
土星 距离太阳14亿公里
与地球相比 土星实在太特别了 Compared to Earth, Saturn is so alien
人们很难想象二者是以相同的物质 that it's hard to imagine how it could have grown
形成的 from the same ingredients.
但如果回到足够久远的过去 But go far enough back in time
土星则看上去与地球惊人的相似 and Saturn would appear to be surprisingly familiar.
46亿年前
土星诞生之初 是一个由岩石和冰构成的小世界 Saturn began life as tiny worlds of rock and ice...
它在太空中无序地翻滚着 tumbling chaotically through space.
和地球 火星 金星和水星一样 Just like Earth, Mars, Venus and Mercury,
土星也开始了融合 聚集 生长的过程 they began to merge and clump together and grow.
但与太阳系内层的行星不同 But unlike the planets of the inner Solar System, Saturn was
土星是在我们称之为雪线的太阳系外缘形成的 forming on the other side of a boundary we call the Snow Line...
那里距离太阳过于遥远 十分寒冷 a place where the Sun is so distant and it's so cold,
水只能以固态形式存在 water exists only in its frozen, solid state.
数以万亿计的冰晶颗粒就像岩石一样 Out here, trillions of particles of ice behave just like rock,
为行星的形成提供了不计其数的额外材料 providing huge amounts of extra planetary building material.
在引力的作用下 大量的冰和岩石相互碰撞 Under the force of gravity, this abundant ice and rock collided
结合在了一起 and combined...
这使得年轻的土星变得越来越大 helping the young Saturn to grow into a giant.
关于太阳系中行星的形成过程 人们对其中的细节 The details of how the planets formed in the Solar System is
还不完全了解 这是科学研究的前沿课题 not fully understood. It's cutting-edge scientific research.
因为那毕竟是在45亿年前发生的事 We're talking about events that happened over 4.5 billion years ago,
不过很可能的是 土星曾经是一个由岩石和冰构成的世界 but it seems likely that Saturn was once a world of rock and ice,
其质量可能是地球的10倍到20倍 也许在你的梦境里 perhaps ten or even 20 times the mass of the Earth and it's almost
能想象出自己站立在土星上的类似情景 possible, in your dreams, to imagine standing on its surface.
但是由于它巨大的质量 But because of its immense mass and its place
和在太阳系中所处的位置 土星的这种岩冰形态并没有持续多久 in the Solar System, Saturn didn't remain a rocky, icy world for long.
随着时间的推移 土星变成了一颗截然不同的行星 As it grew older, Saturn became a radically different kind of planet.
在新的行星形成的区域里 In the region in which the young world was forming, there was
不仅有冰和岩石 还有大量的气体 more than just ice and rock - there were large amounts of gas.
土星的大气层开始成形 And Saturn began to gain an atmosphere...
但其规模远不是地球的大气层能比拟的 but on a scale unlike anything we experience here on Earth.
只有从太空中看去 你才会真正意识到 It's not until you see the Earth's atmosphere from space that
地球的大气层是多么薄 you appreciate just how thin it really is.
地球 大气层厚度100公里
太阳系内层的其它行星 And it's a similar story for the other
情况也基本相似 worlds of the inner Solar System.
火星 大气层厚度80公里
金星 大气层厚度120公里
尽管厚度较薄 这些行星的大气层 Despite being relatively thin, these atmospheres can exert
却能够对行星的地表施加强大的作用力 powerful forces on the planetary surfaces beneath.
在地球上 只要用一个密闭容器 你就能看到 On Earth, you can see the effects of an atmosphere with nothing
大气压力的威力 more than a sealed container.
人们很容易忽略大气层的重量 It's easy to forget that the atmosphere has a weight.
我们头顶上方有一根大约100公里长的空气柱 There's a column of air stretching up 100km above my head.
其中有大量的气体分子 它们会产生压力 That's a lot of molecules and it exerts a pressure.
通过这个瓶子的变化 我们就能见识到大气的压力了 You really see it if you look at what happens to this bottle.
我们把瓶子灌满了山顶海拔3000米处的 We've filled it with air from the top of the mountain, which is
空气 about 3,000 metres.
相较于海平面而言 Now, up there, the atmosphere is about 25% less dense
那里的大气密度要低25% than it is down there at sea level.
所以当我们下降时 瓶外的大气压就会增大 So, as we descend, the atmospheric pressure outside is increasing
而瓶内的气压等同于 and the pressure in here is just what it
山顶的情况 所以我们可以直观的看到 was at the top of the mountain and so, you see visually that
大气压力的作用 瓶子被压扁了 force in action and that is squashing the bottle.
这就是物理效果 Physics in action!
很厉害吧 It's brilliant, isn't it?
仅仅几百米落差的大气压就能压扁一个瓶子 While just a few hundred metres of atmosphere can crush a bottle...
如果大气层足够大的话 就能改变整个星球的面貌 if an atmosphere gets big enough, it can transform an entire planet.
46亿年前
在土星诞生后的几百万年里 Within just a few million years of its birth...
它依靠聚集岩石和冰 尽可能地变大 Saturn had grown as large as it could, from rock and ice alone.
现在它转向了另一种物质材料 And now, it turned to another building material -
太阳形成时残留下来的氢气和氦气 the hydrogen and helium gas left over from the formation of the Sun.
这两种气体质量太轻 太阳系内层 This gas would have been too light for the smaller
体积较小的行星无法束缚它们 worlds of the inner Solar System to hold on to.
但土星的巨大质量所形成的强大引力 But Saturn's great mass created gravitational forces powerful
却足以让它们聚拢过来 enough to draw it in.
数以万亿吨计的氢气和氦气 Trillions upon trillions of tonnes of hydrogen
开始包裹在这颗行星的表面 and helium gas began to envelope the planet.
随着新大气层的增长 And as this new atmosphere grew,
它也改变了下方的行星地表 it transformed the surface below.
气体重量所产生的巨大压力使得岩石和冰的温度急剧上升 Enormous pressures, created by the weight of this gas, heated rock
这颗行星开始放出光芒 and ice so much, they began to glow.
当土星成年时 其表面的压力达到了 As Saturn matured, the pressure at the surface rose
地球大气压力的1000万倍 to ten million times the atmospheric pressure on Earth.
在如此大的压力下 Under those kind of pressures,
物质的表现也变得怪异起来 matter behaves in extremely strange ways.
地表的概念已经毫无意义了 The very idea of a surface becomes meaningless and Saturn was
土星从一颗寒冷的 transformed from an icy,
岩石行星 变成了完全另类的行星 rocky world into a completely different class of planet -
气态巨行星 a gas giant.
土星变得极其巨大 Saturn was now so big,
可以容纳近5000颗相当于地球大小的星球 it could contain nearly 5,000 Earth-size worlds.
但这颗巨大的原始行星与我们现在所看到的土星 But this vast, wild protoplanet was totally unlike the Saturn
全然不同 we see today.
要了解土星是如何形成的 To discover how that world emerged,
我们就必须发射探测器近距离地观察它 we had to send spacecraft to meet it close up.
点火成功 泰坦四号运载火箭升空 它搭载了 We have ignition and we have liftoff of the Titan Centaur carrying
两个“旅行者”号探测器中的第一个 the first of two Voyager spacecraft to extend Man's senses
“旅行者”号 1977年
人类的触角将前所未有地伸向太阳系的深处 farther into the Solar System than ever before.
65000个独立部件
造价 8.65亿美元
返回报告显示两部大功率火箭发动机运转良好 Reports coming back indicate those twin large solid motors are
每部发动机能产生120万磅的推力 functioning perfectly, producing 1.2 million pounds of thrust each.
“旅行者”2号 前往土星的时间 4年
返回的导航数据表明航向完全正确 The guidance data coming back shows that we're right on the money.
它到了 It's there!
“旅行者”2号在太空经过长达4年的飞行后 终于抵达了土星 Voyager 2 has reached Saturn after four years in space.
它比预计时间到得稍早了些 准确地说早了2.7秒 It got there just a bit early, 2.7 seconds early, to be exact,
航程达到了16亿多公里 after a flight of a billion and a quarter miles.
“旅行者”号探测器让我们第一次详细地观测到了土星 The Voyager probes gave us our first detailed look at Saturn,
得以高分辨率展现这颗行星的真面目 revealing the planet in exquisite resolution.
我们收获了大量的照片 There's just an amazing harvest of pictures.
卡尔·萨根 （1934.11.9－1996.12.20）因《宇宙：个人游记》而享誉全球 美国天文学家 天体物理学家 宇宙学家 科幻作家 非常成功的科普作家
“旅行者”2号拍摄了上万张土星 You know, there's tens of thousands of photographs of Saturn
及其行星环和卫星的照片 and its rings and its moons taken by the Voyager 2 spacecraft.
这是我们第一次有机会 For the very first time,
详细研究土星的巨大大气层 we were able to study Saturn's vast atmosphere in detail.
土星本身是由氢和氦构成的 Saturn itself is composed of hydrogen and helium.
在这里我们看引了奇异的气象现象 And we are seeing an exotic meteorology here.
“旅行者”号明确显示土星的上层大气 Voyager showed, beyond doubt, that Saturn's upper atmosphere was
几乎完全是由氦气和氢气构成的 made almost entirely of helium and hydrogen...
在早期的太阳系中 这两种气体极为丰富 the very same gases so abundant in the early Solar System.
但这个一度混乱的大气层 But this once chaotic gas was now organised
现在形成了复杂的天气系统 into intricate weather systems.
其中有一个现象 最令“旅行者”号研究团队感到意外 And one, above all others, took the Voyager team by surprise.
云层中有一个巨大的六边形结构 A huge hexagonal structure in the clouds,
大到足以容下整个地球 so big it could fit our entire planet within it,
而且几乎是地球的4倍以上 nearly four times over.
土星的大气层显然要比我们所想象的 The atmosphere of Saturn was revealing itself to be stranger
更奇异 更具活力 and more dynamic than we could ever have imagined.
大气层是最壮观 Atmospheres are some of the most spectacular
最复杂的行星环境之一 and complex planetary environments.
很少有人能这样观赏阿尔卑斯山 真的 真是太棒了 Not many people see the Alps like this! Seriously! It's so great!
我还担心你会晕机 太壮观了 I was afraid that you'd just get too sick or something. It's awesome!
很好玩 伙计 Man! It's fun, man!
确实很好玩 This IS fun!
所有行星的大气层都有其独特之处 The atmosphere of every planet takes on its own unique character.
但是它们的驱动力和内部的天气系统究竟如何 But what powers them and the weather systems within
就要取决于它们在太阳系里的位置了 depends on where you are in the Solar System.
地球上的大部分天气都是由太阳的热量驱动的 Most of the weather on the Earth is driven by the Sun.
阳光加热了下面的地表 It heats the ground up down there and that, in turn,
使得贴近地面的空气升温 然后膨胀 heats the air up close to the ground, makes it expand,
也就是说大气密度会下降 热空气上升 and that means that the air becomes less dense and the hot air rises.
这样就形成了热气流 That means you get thermals, so energetic
也就是地表空气到高层大气的能量运动 movements of air from the ground into the upper atmosphere.
我们现在滑翔机所利用的就是热气流 And that's what we're exploiting now, to glide.
所有这些美丽的天气都是由太阳驱动的阳光加热大地 All this beautiful weather is driven by the Sun heating the land
使空气流动起来 and causing air to move around.
所以我们实现了航行 So we're sailing around...
航行于这美丽的 翻滚的 Sailing around in a turbulent,
流动的空气之中 moving ocean of air.
但是在太阳系中更加遥远的行星上 But travel further out into the Solar System
大气的驱动力就不会是太阳了 and the driving forces within an atmosphere must change.
土星上的大气已经存在40多亿年了 Now, there's been weather on Saturn for over four billion years,
可是土星距离太阳非常遥远 but Saturn is a long way from the Sun, and so
所以那里的大气系统不主要依靠太阳的热量驱动 those weather systems are not primarily driven by the Sun's heat.
而土星上却有着太阳系中 And yet the storms on Saturn are amongst the most violent
最猛烈的风暴 found anywhere in the Solar System.
土星上的光照强度几乎只有地球上的 With sunlight almost 100 times weaker on Saturn than it is
百分之一 here on Earth...
这意味着驱动土星天气的是其它因素 it means something else is helping drive its weather...
土星大气中的巨型复杂结构也是如此 and the huge, complex forms that arise in its atmosphere.
通过研究土星云顶及其巨大的风暴系统 By studying the cloud tops of Saturn and its great storm systems,
我们现在可以对土星大气层下面的奇异世界进行大举推测 we can now infer a great deal about the strange world that lies beneath.
判断这颗星球的能量来源 And the energy source that helps power this planet.
在上层大气之下 Below the upper atmosphere,
大量的水汽云叠涌堆积 great clouds of water grow.
威力比地球上强一万倍的闪电照亮了天空 Lightning 10,000 times more powerful than on Earth illuminates the sky.
闪电将甲烷气体变成了大片的烟灰云 This lightning transforms methane gas into huge clouds of soot.
越向下 Deeper still,
压力越大 the pressures grow so great that these
这些碳灰很可能会被转变成钻石 chunks of soot are likely transformed into diamonds.
但即便是这些钻石最终也会瓦解于土星的压力 But even these diamonds will succumb to the pressures of Saturn,
最终液化 eventually liquefying.
要到达土星表面4万公里以下 It's not until 40,000km down
才能看到它最大的能量来源 that the major source of Saturn's energy is revealed.
这里的压力非常之高 气体的表现上就像是液态金属 Here, pressures are so intense, gases behave like liquid metal.
熔化的氦气如雨般在氢气中落下 Molten helium falls like rain through hydrogen...
释放出惊人的热量 and releases incredible amounts of heat.
我们认为这是一种非常特殊的热源 And we think that this is the extraordinary heat source
始终在为土星的天气提供着动力 that has been helping to drive Saturn's weather.
在土星诞生后的几亿年里 Within just a few hundred million years of its birth,
它的生活跌宕转折 Saturn had lived a life of drama.
在之后的十几亿年间 它几乎没有变化 Now, it remained largely unchanged for billions of years,
不过与我们现在所看到的土星仍有很大的不同 although still very different from the planet we know today.
随着时间的推移 土星的巨大规模 But in time, this great size
又将导致另一个标志性的转变 would lead to one more iconic transformation.
土星是一颗以行星环为特征的行星 Saturn is a planet defined by its rings.
如果让一个孩子画一颗行星 You get a child to draw a planet and quite
他们画的很可能会是土星的样子 a lot of the time, they'll draw something that looks like Saturn.
如果近距离观察 土星环难以置信的精致和复杂 Close up, they are almost impossibly delicate and intricate.
它们是由数以万亿计的冰晶构成的 They're made up of trillions of ice crystals, most of them
大部分冰晶都和雪花差不多大 但有些却有房子那么大 no bigger than snowflakes, but some of them as large as houses.
如果我们用望远镜观察 Now, if you look through a telescope,
就会发现土星环的反光率很高 they're highly reflective.
它们反射太阳光的能力和土星本身差不多 They reflect sunlight back just as powerfully as the planet itself.
但是这就出现了一个有意思的问题 But that raises an interesting question,
因为太阳系里遍布着尘埃 because the Solar System is full of dust.
假若一颗冰晶 Any ice crystals that hang around
在这里停留一段时间后都会变脏 for any amount of time will get dirty,
然后反光率就不会很强 就不会那么明亮了 and so they won't reflect sunlight back, they won't be as bright.
那么问题来了 为什么土星环的反光率会这么高呢 So, the question is, why then are Saturn's rings so reflective?
答案来自最大胆 The answer came from one of the most audacious
最成功的一次太阳系外层飞行计划 and successful missions to the Outer Solar System.
5 4 3 2 1 “卡西尼”号探测器升空 Five, four, three, two, one, and liftoff of the Cassini spacecraft
踏上长达16亿公里前住土星的旅程 on a billion-mile trek to Saturn.
“卡西尼”号探测器 1997年
火箭已离开发射塔 点火20秒 所有系统正常 We have cleared the tower. T plus 20 seconds. All systems are go.
“卡西尼”号探测器将近距离研究土星 The Cassini probe was designed to study Saturn and its moons
土星环及其卫星 从而寻找土星起源的新线索 and rings up close, to shed new light on their origins.
所有系统继续运行 All systems continuing to be go.
“旅行者”号探测器只在土星附近逗留了几天 But whereas the Voyager probes spent only days at Saturn,
然后就飞驰而过了 而“卡西尼”号探测器则旨在进入土星轨道 as they sped by, Cassini was built to enter Saturnian orbit...
火箭助推器已脱离 Solid rocket boosters have been jettisoned.
速度约为每小时5600公里 Velocity 4,378 miles per hour.
它将对土星做长达数年的探索 And explore the system for years.
“卡西尼”号的质量比“旅行者”号要大很多 Many times more massive than Voyager, Cassini had to take
它必须沿另一条路线才能进入土星附近的轨道 a different route to enter orbit around Saturn.
为了节省燃料 它飞越了多个行星 To conserve fuel, it flew by multiple planets,
借助行星引力弹射完成加速 slingshotting past them to pick up speed
和航向调整 整个行程需要7年时间 and change direction over the course of seven years.
6号站 “卡西尼”号 Station 6, Cassini is...
当“卡西尼”号终于接近目标时 As Cassini finally approached its target,
它正以每小时近10万公里的速度飞行 it was travelling at almost 100,000 kilometres per hour
必须以非常精确的方式完成减速 and had to slow itself with exquisite precision.
喷气推进实验室控制中心
多普勒雷达已展开
经过35亿公里的飞行 After its 3.5 billion-kilometre journey,
“卡西尼”号探测器能够以前所未有的清晰度观测土星环了 Cassini was now able to see Saturn's rings like never before.
此外 “卡西尼”号在土星附近停留的时间很长 What's more, during its long stay at Saturn, Cassini would be able
它将首次对土星环进行实际取样 to take physical samples for the very first time.
通过测量太阳系尘埃落在土星环上的方式 By measuring the way that the dust from the Solar System falls
“卡西尼”号取得了一个惊人的发现 onto the rings, Cassini made a startling discovery.
如果说土星环在土星周围已经存在数十亿年 If the rings have been around Saturn for billions of years,
那么它应该会被尘埃所遮蔽 变得暗淡 they should have been darkened and dimmed by the dust.
可是土星环依旧光亮如新 But they are pristine and bright.
原因就在于土星环还很年轻 And the reason is because they are young.
比土星本身年轻了近45亿年 Nearly 4.5 billion years younger than Saturn itself.
土星环起源之迷是一个活跃的研究领域 The mystery of the origin of the rings is an active area of research.
“卡西尼”号所提供的证据表明 And the evidence that Cassini delivered hints that the solution
迷题的答案不在于土星本身 lies not with the planet itself,
而在于土星轨道之上的 but with the world's tracked in orbit around it -
土星的卫星 Saturn's moons.
土星有62颗大卫星和无数的小卫星 Saturn has 62 large moons and countless smaller ones -
至今仍在不断发现 we're still discovering them.
所以土星系统本身上就像是一个迷你的太阳系 So it's like a mini solar system in itself.
这些卫星大小各异 有行星大小的土卫六 And those moons range in size from planetary-size objects,
也有形状不规则的小石块 like Titan, to small irregular-shaped lumps of rock.
而且它们在大小 形状和表面特征上 And there's so much diversity in size and form
各有不同 这使整个系统就像一本历史书 and surface features, that the whole system is like a history book.
如果我们能读懂它 我们就会发现 And if we learn to read it then we see that Saturn
土星极其动荡而多变的过去 has had a very violent and changeable past.
看这个 这就是土卫一 它被称为死星的原因 Look at this, this is Mimas, which is often called the Death Star moon
显而易见 for obvious reasons.
它有一个巨大的撞击坑 这说明很久以前 It has this huge impact crater, which tells you that once, long ago,
土卫一
曾经有过一次剧烈的撞击 there was a very violent impact
险些就彻底摧毁了这颗卫星 that almost - but not quite - destroyed the moon.
这是土卫八 And this is Iapetus.
这是一个非常大的卫星 几乎有行星大小 It's a very large moon, almost planetary-size.
直径约1500公里 It's about 1,500 kilometres across.
它有一半是白色 一半是黑色 And half of it is white, and half of it is dark.
土卫八还有另一个独特的特征 Iapetus also has another distinctive feature
那就是赤道附近的山脊 which is this ridge all the way around the equator, and you can see
它在这张照片上也很清晰 the scale of it from this photograph.
可见它的规模有多大 And this is clearly visible.
它是太阳系中最高的山脉之一 It's one of the highest mountain ranges in the Solar System,
高度落差达到了20公里 20km from peak to the ground below.
人们认为它的形成 是因为这颗卫星曾经有一道星环 And it's thought that this formed because a ring that was once
就像土星环一样 后来它掉落到了土卫八的表面 around the moon, just like Saturn's rings, collapsed onto its surface.
“卡西尼”号继续飞行 它让我们清晰地看到了 As Cassini continued its journey, it revealed in detail multiple moons
几颗几乎完全由冰构成的卫星 made almost entirely of ice.
许多位于土星环内或是周围的卫星 And many of them had taken on extraordinary forms
造型都很奇特 in and around the rings.
土卫十八 直径28公里
土卫七 直径266公里
土卫五 直径1528公里
“卡西尼”号探测器对冰质卫星有了更为细微的分析 As Cassini analysed the ice moons in ever greater detail,
人们发现它们中的许多都是由与土星环 it became apparent that many of them were made of exactly
完全相同的物质构成的 the same material as the rings themselves.
土星环和土星的卫星有着千丝万缕的联系 The rings and moons were profoundly linked.
“卡西尼”号看到了这么多的土星卫星 But for all the moons that Cassini saw,
可是似乎却少了一颗 it now seemed likely that one was missing.
1亿年前
在恐龙统治地球的时代 When dinosaurs roamed the Earth,
我们怀疑土星的轨道上有一颗卫星不见了 we now suspect Saturn had a moon in orbit that no longer exists.
一颗直径或许约有400公里的卫星 A moon perhaps 400km across
几乎完全由冰构成 and formed almost entirely of ice.
可是它的命运已经注定了 But this world was doomed.
它的轨道距离土星太近了 无法抵抗土星 It found itself orbiting too close to resist the immense forces
巨大的引力 of Saturn's gravity.
引力塑造了土星系统 Gravity is the sculptor of the Saturnian system
也是其内在变化的动因 but also the instigator of change within it.
我们住往认为引力是将物质聚集在一起的力量 We tend to think of gravity as a force that pulls things together,
但它也能造成事物的毁灭 but it can also act to rip things apart.
想想地球上的潮汐 它们是由月球 Think of the tides here on Earth, they're caused by the difference
对于地球两侧的引力差 in gravitational pull of the moon from one side of the Earth
引起的 to the other.
这种引力差可以很小 但也很强大 And that difference which can be quite subtle is also powerful,
它能移动整个海洋 it can move entire oceans.
这叫作潮汐引力 但地球对月球也有潮汐效应 It's called tidal gravity, but the Earth also has a tidal effect
因为地球是个完整的行星 on the moon, and because the Earth is an entire planet
所以这种效应会更强 that effect is much more powerful.
地球的引力足以导致月球表面变形 The pull of the Earth is enough to deform the moon's surface.
在45亿年前 月球到地球的距离比现在近了17倍 The effect was particularly strong 4.5 billion years ago
这种效应尤其强烈 when the moon was nearly 17 times closer.
当时地球的拉动力导致了月球表面坚固岩石的 Back then, the pull from the Earth caused a tide of solid rock
升降起伏 to rise and fall.
如果月亮再近一点 就会超过所谓的 If the moon had been any nearer it would have crossed what we call
洛希极限 潮汐引力就会增强 the Roche limit, a place where tidal gravitational forces are so strong,
导致卫星四分五裂 moons can get ripped apart.
古罗马人以他们的农神萨图努斯来命名土星 The Romans named the planet Saturn after their god of time and harvest.
在古代神话中还有一个更可怕的传说 And in one of the more gruesome tales from classical mythology,
萨图努斯吃掉了自己刚出生的孩子 为了不让他们 Saturn actually ate his newborn babies in order to prevent them
夺走他的权力 from taking his power.
有意思的是 “卡西尼”号探测器让我们了解到 What's sort of interesting is, that what we've learned from Cassini
至少从比喻的角度来说 这名字挺合适 is that, at least metaphorically speaking, they weren't far wrong.
土星 1000万-1亿年前
如今的主流理论认为 当时在土星大气层之外 Just beyond Saturn's atmosphere, our leading theory suggests
一定有一颗冰质卫星靠近过 an icy moon must have approached close to
甚至是进入了土星的洛希极限之内 or even just inside the planet's Roche limit.
当土星巨大的潮汐引力 As Saturn's immense tidal gravitational forces
作用于这颗卫星时 它开始分裂 acted across the moon, it began to rupture.
土星开始吞噬它的“孩子” Saturn began to devour its child.
在土星周围的轨道上 Up to 15,000 trillion tonnes of ice
多达1.5亿亿吨的冰体支离破碎 broke apart in orbit around Saturn.
由于移动速度很快 Because of the speeds the ice fragments were travelling,
碎冰很可能在几天之内就扩散开来 it's likely that in just a few days they spread out
形成了这颗巨大行星之外的环 to encircle the great giant.
标志性的土星环就此诞生了 Saturn's iconic ring had been born.
如今巨大的土星环也发生了一些变化 Today, the giant ring has evolved.
土星强大的引力场使得它保持了 Saturn's powerful gravitational field has helped keep
近乎完美的圆形 its near perfect circular shape.
不过内部的碰撞导致它扁平扩散开来 But collisions within have caused it to flatten out.
碎片形成了一个比木星还要宽的圆环 Now this debris forms a disc wider than Jupiter,
而平均厚度却只有10米 yet, on average, just ten meters thick.
在土星环内部 一些月球大小的冰块环绕着土星运动 Within, moon-sized chunks of ice orbit the structure
清除出开阔的空隙带 clearing great voids.
这就把原来的一道环 Turning one ring...
变成了许多道环 into many.
在一些地方 卫星把冰颗粒向上拉起 In places, moons have pulled particles of ice upwards
形成超过两公里高的尖峰 to create strange peaks over 2km high.
在合适的条件下 And in just the right conditions,
这些冰峰就会在土星环上投下壮观的阴影 they cast spectacular shadows across the rings.
这个曾经不起眼的由岩石和冰构成的世界 This once tiny world of rock and ice...
历经了众多天翻地覆的剧变 that has undergone so many great transformations...
如今的它成为了太阳系中的一颗瑰宝 has today become the Solar System's jewel.
“卡西尼”号探测器加深了我们对土星 Cassini had deepened our understanding of the origin
起源和演化的认识 and evolution of Saturn.
但它的使命还远没有结束 But its mission was far from over.
因为就在土星环之外 它又发现了另一个宝藏 Because just beyond the rings it discovered another treasure.
有可能解答我们对于太阳系及其以外 A place that may hold answers to some of our deepest questions
生命存在可能性的一些最深层问题 about the possibility of life in the Solar System and beyond.
土卫二位于土星环的外缘 Over a billion kilometres from the warmth of the sun,
距离温暖的太阳 just on the outer edge of Saturn's rings,
有十亿公里 lies the icy moon Enceladus.
土卫二是一颗很小的卫星 Enceladus is quite a small moon,
只相当于冰岛那么大 it's only about the size of Iceland actually.
但这并不意味着它乏善可陈 But that does not make it dull.
它是太阳系中反光率最高的天体 It is the most reflective object in the solar system -
超过90%的光线都被反射了回去 over 90% of the light that hits it bounces back,
这是因为它的表面覆盖着纯净的冰 and that's because its surface is covered in pure ice.
同时也遍布着裂缝 It's also crisscrossed by crevasses
就像我们在冰川上看到的那样 like this one you see in this glacier,
只不过规模更为庞大 but on a much grander scale.
最大的一条被称为虎纹 The largest, known as the tiger stripes,
有100多公里长 are over 100km long.
尽管土卫二的地表很美 But for all its surface beauty,
但它真正与众不同之处 it's what's going on below the ice
还在于地表之下 that makes Enceladus so special.
我们在土卫二的冰层下所取得的发现 What we found beneath Enceladus's shell of ice must rank
可以说是21世纪太空探索领域最伟大的发现之一 as one of the greatest discoveries in 21st-century space exploration.
但这也是一个很容易被人们忽略的现象 But it was a discovery that had been hiding in plain sight.
这是一张“旅行者”1号在1980年拍摄的土卫二的照片 This is a photograph taken by Voyager 1 of Enceladus in 1980.
当时没有人看出有什么特别之处 Now, nobody noticed anything remarkable about it at the time
现在这幅图像被增强处理过了 现在我们可以看到 but this image has been enhanced and now you can see
在卫星的这一侧有这种模糊的斑点 this sort of misty blob off one side of the moon.
这很有意思 Now, that is fascinating.
这说明有什么东西从土卫二的内部冲向了太空 It means something is rising up from inside Enceladus.
当“卡西尼”号探测器在24年后到达那里时 它也看到了同样的情形 Now, when Cassini got back there 24 years later it saw the same thing,
但这次的细节更为清晰了 but this time in much more detail.
当“卡西尼”号探测器接近土卫二时 人们立即发现了异常之处 As Cassini approached Enceladus, the anomaly revealed itself.
巨大的水蒸气和冰体从卫星的表面喷发出来 Giant plumes of water vapour and ice were erupting from its surface.
每秒喷发出的物质超过了200公斤 Over 200kg of material was being released every second.
但这些物质并没有散逸到太空中去 But this material was not lost to space.
却像是在填补土星的一个外环 It seemed to be feeding one of Saturn's outside rings,
使它更加完整 helping to replenish it.
这些发现让研究人员决定尝试一次大胆的冒险 And these discoveries inspired an audacious risk.
他们要在10亿多公里外 Piloted from over a billion kilometres away,
引导“卡西尼”号靠近那些危险的羽流 Cassini was guided dangerously close to the plumes.
探测器从距离土卫二表面不到48公里的上空 The craft passed within just 48km of the surface
掠过 of Enceladus.
“卡西尼”号真正接触到了那些羽流 And Cassini was able to touch the plumes.
经过探测器连续多次的飞越 我们取得了 What we discovered, thanks to a series of these flybys,
令人叹为观止的发现 was breathtaking.
羽流中的冰实际上是冻结的海水冰晶 The ice in the plumes was actually frozen particles of salty water.
我们发现了一个在向太空渗漏的地下海洋 We had found a subsurface ocean leaking into space.
土卫二距离太阳极为遥远 Far, far from the sun,
它的表面下藏匿着一个液态的海洋 Enceladus was harbouring an ocean of liquid water.
而这片海的存在也是由于土星的原因 And it was there because of Saturn.
土卫二以椭圆轨道绕土星运行 Enceladus orbits Saturn in an elliptical orbit,
这意味着土星对土卫二施加的引力大小 which means the gravitational forces across the moon
是不断变化的 are constantly changing.
土卫二之所以形成这样的轨道 是由于受到了另一颗较大的卫星 It's maintained in this orbit by the pull of another larger moon -
土卫四的引力作用 Dione.
持续变化的引力拉伸和挤压着土卫二的内部 These ever shifting gravitational forces stretch and squeeze
加热融化它的冰质内核 its heart, warming and melting its icy interior.
“卡西尼”号取得的发现数据还存在另一个惊喜 But Cassini's data had one more surprise in store.
我们在对水冰羽流进行更为详细的分析后 As the plumes of water ice were analysed in ever greater detail,
我们发现了 we discovered complex organic compounds
只会来自深海热泉喷口的 and silica particles that could only have come
复杂有机化合物和硅微粒 from hot hydrothermal vents.
在寒冷的太阳系外缘 In the frozen outer reaches of the Solar System
我们居然发现了一处温暖湿润的绿洲 we had found a warm watery oasis.
“卡西尼”号让我们看到了土卫二冰层下的景象 Cassini has given us a glimpse beneath the ice of Enceladus,
从科学意义上讲这是真正吸引人的地方 and it is fascinating genuinely in a scientific sense because many
因为许多生物学家相信像这样的热泉喷口 biologists believe that hydrothermal vents like those that are almost
几乎可以肯定存在于土卫二的海底 certainly present on the floor of Enceladus's ocean
热泉就是地球生命的摇篮 were the cradle of life on Earth.
所有的成分都齐备 All the ingredients are present -
有热水与冰和矿物质的接触 there's hot water in touch with ice and minerals.
这就是个巨大的化学反应炉 That's a reactive cauldron of chemistry.
有活性气体 甲烷 There are reactive gases - methane.
“卡西尼”号在羽流中发现了氢分子 Cassini found molecular hydrogen in the plumes,
这是地球上原始生命的食物来源之一 and that was one of the food sources of primitive organisms on Earth.
所以说现在土星外围的轨道上 So there really is a possibility that there is life
确实有存在生命的可能性 in orbit around Saturn today.
土卫二上存在生命的预期令人兴奋 The prospect of life on Enceladus is exciting.
但即便那里存在 也只可能是最简单 But if it's there, it's likely to be only the simplest
最原始的生物 and most primitive of organisms.
而且 由于土星曾经的动荡和善变 And given how violent and changeable Saturn's past has been,
这个由冰体和液态水构成的世界或许只是不久前 this world of ice and liquid water may only have arisen
才出现的 relatively recently.
我们不清楚土卫二 Now, we don't know how long
进入地质活跃期多长时间了 也不知道它的海洋存在了多久 Enceladus has been geologically active, how long its had an ocean.
如果说只有1000万年 哪怕是几亿年的话 If it was only tens of millions or even hundreds of millions of years,
那么这段时间还不足以发展出生命 that may not have been enough time for life to get going.
但是如果那里有生命存在 我们就可以预知未来了 But if there is life there then we can glimpse its future
因为如今地球上仍然存在深海热泉喷口 because there are still hydrothermal vent systems present on Earth today
那里的生命不仅生存了下来 而且十分兴旺 and life doesn't just survive there, it thrives.
热泉喷口通常位于深海下的地壳断裂带中 Often found in the deep oceans along fault lines in the Earth's crust,
那里是地球上最丰富 最复杂的 hydrothermal vents are some of the richest and most complex
生态系统之一 ecosystems on Earth.
这样的栖息地供养了 Feeding off the abundant bacteria that breed there,
众多奇异而复杂的生物 它们以大量繁殖的细菌为食 these habitats support a multitude of strange and complex organisms.
尽管这样的生物永远不会出现在土卫二上 Whilst creatures like this will never exist on Enceladus,
但几十亿年后 那个遥远的世界 billions of years from now, it is just possible that this
也许会形成自己独特的生命家园 distant world may become home to its own unique forms of life.
不过对“卡西尼”号探测器来说 土卫二冰层下的新奇世界 But for Cassini, the brave new world under the ice of Enceladus
却是一个令人喜忧参半的发现 was a bittersweet discovery.
2017年9月15日
绕土星飞行13年后 13 years after it arrived at Saturn,
“卡西尼”号的燃料终将耗尽 Cassini's fuel finally began to run dry.
美国国家航空航天局不敢冒险让这台探测器坠毁在土卫二上 NASA couldn't risk letting this probe crash land on Enceladus
避免污染一片潜在的生命温床 and contaminate a potential habitat for life.
这里是1号飞行控制台 Systems, ACS One.
我们刚切换到高速模式 We've just had transition to high rate mode.
喷射推进实验室控制中心
于是他们决定让“卡西尼”号进行最后一段飞行 And so the decision was made to send Cassini on one final journey.
它会飞向 A journey that would take it
土星的大气层内 into the atmosphere of Saturn itself.
那里将会是它的使命终结之地 A journey from which it would never return.
我们进入大气层了 And we are in the atmosphere.
无线电信号 Radio signal still holding.
存在30秒 30 seconds.
我们刚刚得知45秒后 Just heard the signal from the spacecraft is gone
探测器发出的信号会消失 探测器也将坠毁 and that, within the next 45 seconds, so will be the spacecraft.
土星见证了太阳系历史上的 The planet that had borne witness to some of the greatest dramas
一些最壮观的场面 现在却在吞噬 in the history of the Solar System was now consuming the craft
讲述它非凡故事的探测器 that had told its extraordinary story.
“卡西尼”号探测器和土星最终融为一体 Cassini and Saturn had now become inseparable companions.
经过长途飞行我们前往土星 去体验和探索 We journeyed out to Saturn to experience and explore
这至美的景色 this great beauty.
但最终 我们会在地球上提升对宇宙的认知 But in the end we were rewarded with insights closer to home.
“卡西尼”号测器和它的科研团队 Cassini and her team of scientists and engineers
称得上是最伟大的探险家之一 should be counted amongst our greatest of explorers.
这项任务具备探险的所有要素 The mission had all the ingredients -
一艘飞船和它的船员 穿越未知的海洋 a vessel and a crew drawn by the prospects of beauty
前往陌生世界 探索和了解美丽的新事物 and new knowledge across an uncharted ocean to an alien world.
正如探索中经常遇到的情形一样 And, as is so often the case in exploration,
真正的宝藏总是隐藏在出人意料的地方 the real treasure was found in the unexpected shadows.
这一次是在土星环的阴影之中 In this case, in the shadow of the rings,
我们发现了土卫二的小小世界 where we found this tiny world, Enceladus,
它或许能孕育生命 这让我们更加确信 that may harbour life and provide us with reassurance
人类在宇宙中并不孤单 that we are not alone in the universe.
看 这就是我们的发现之美 See? The beauty is in the story.
如果我们真在土卫二上发现了生命 会有意义吗 Would it matter really if we found life on Enceladus?
毕竟只是些微生物 It would only be microbes after all.
是的 而且很重要 Yes, it would matter.
我认为我们正处在历史上的一个阶段 我们需要一种自我认可 We are at a time in our history, I think, where we need reassurance
或者说是提醒 在我们的世界之外还存在着美和知识 or perhaps a reminder that there is beauty and knowledge
甚至是生命和意义 这很重要 and perhaps even life and meaning beyond our shores.
我确信 我们还会再次前往土星和它的卫星 We will, I'm sure, go back to Saturn and its moons,
做更深入的探索 停留更长时间 explore deeper, stay longer,
或许有一天我们甚至会亲自拜访 and maybe one day even visit ourselves.
我们不知道会发现什么 We don't know what we'll discover
但有一点是可以肯定的 这个故事才刚刚开始 but we can be sure that the story has only just begun.
《行星》幕后故事
“卡西尼”号是有史以来最成功的探测器之一 Cassini has been one of the most successful probes ever flown.
但是建造一台能够在太阳系外层空间 But constructing a machine that could survive 13 years
飞行13年的探测器 对每个参与其中的人来说都是极大的考验 in the outer Solar System was a huge challenge for everyone involved.
点火20秒 T plus 20 seconds.
他们提议建造“卡西尼”号探测器的时候 Even when they were proposing Cassini, I thought,
我就觉得不可能 根本就不可能 "No, no, this is never going to happen."
卡尔·穆雷教授 伦敦玛丽女王大学
感觉太不现实了 It's, like, maybe too ambitious or something.
很难算出有多少人参与 It's difficult to put a number on how many people
米歇尔·杜啥提教授 “卡西尼”号首席调查员
“卡西尼”号的计划 were involved in Cassini.
我觉得至少是上万人 Tens of thousands, I would say.
这是一项极其复杂的工程 This is a very, very complex effort.
线路总长超过了16公里 There's over ten miles of wiring
而且每根线都必须检查 and you have to check out every wire.
所以我们花了两年半才把它组装起来 So it took us two and a half years to put the thing together.
朱莉·韦伯斯特 “卡西尼”号首席工程师
我们所有人为了那一刻投入了大量的心血 All of us spent a lot of effort to get to that moment
卡罗琳·博尔克 “卡西尼”号成像科学分系统团队负责人
所以对它的感情是非常深的 so there's a lot of emotion attached to it.
当我们看到它发射升空时 And then you see it launch
我们知道它要前住一个非常非常遥远的地方 and you know that it's on a journey to a very, very distant place...
感觉好像自己的心也跟着去了 and so you feel like you're going too.
当“卡西尼”号首次向地球发送近距离照片时 When Cassini first began to send close-up pictures back to Earth...
对整个团队来说 那是个非常特别的时刻 it was a special moment for the whole team.
他们第一次接收传回的数据时 I was sitting in what they call the Blue Room
我正在所谓的蓝室里面接受采访 being interviewed while they were beaming for the first time
杰夫·库奇 “卡西尼”号土星环科学家
然后其中一张照片出现了 我喊道 and then one of these pictures came on and I just went,
哇 快看 "Wow, look at that!"
那一刻我真是高兴得要跳起来了 That was really the jumping out of the chair moment for me.
而那不过是第一天 And it was just the first day.
我们看到的是从未有过的最高分辨率的图像 What we were seeing was the highest resolution that had ever been seen.
我看到了一些现象 I saw phenomena that I'd only seen
以前只在计算机模拟中看到过 in, kind of, computer simulations before
那是我第一次亲眼看见 and now I was seeing it for the first time
才意识到这一切都是真的 and realising all this was real.
我们在土星环上看到的细节 And we were seeing details in the rings
实在是太震撼了 that were shocking... shocking.
我们根本没有那种想象力 We just lacked the imagination that it would require
去预判它会是什么样子 to predict what it would look like.
对我而言 当那张背光照片出现的时候 For me, when that great backlit picture came out,
给我的触动是非常大的 that's when it hit for me.
天呐 我们做到了非常独特而美妙的事情 "Oh, my God, we've done something really unique and wonderful."
那是个了不起的成就 It was like, "This is going to be... This is going to be huge."
在“卡西尼”号长达13年的土星之旅期间 Over Cassini's 13 years at Saturn...
它探索了土星上不可思议的风暴 it explored the planet's incredible storms.
研究了土星环的形成 The formation of its rings.
还发现了土卫二上的地下海洋 And discovered the oceans of Enceladus.
但“卡西尼”号最伟大的成就或许还在后面 But Cassini's greatest insights may be yet to come.
数据中有极其丰富的信息 There's such a wealth of information in the data.
我想我们只解读了冰山一角 I think we've just skimmed the top of the data.
我相信在未来的30到40年间 我们还会从“卡西尼”号的数据中 I think people will continue to make discoveries from Cassini data
取得更多的发现 for another 30 to 40 years.
“卡西尼”号在它的最后时刻所收集到的数据 The data Cassini collected in its final moments
已经改变了我们对这颗行星的认知 is already changing our understanding of the planet.
它揭示了土星环正在消失 It has revealed the rings are disappearing.
每秒有多达10吨的物质 As much as 10,000 kilograms of material
在落向土星 is falling into the planet each second.
现在看来 也许一亿年之后 It now seems likely that just 100 million years from now,
美丽的土星环就将不复存在了 Saturn's great rings will be no more.
“卡西尼”号向我们证明了 我们能看到如此神奇的美景 Cassini has shown us that we have been uniquely fortunate
是多么的幸运 to behold this great beauty.
下集预告
我们朝黑暗进发 We head into the darkness.
前往冰巨行星 天王星和海王星 To the ice giants - Uranus and Neptune.
在更远处 And beyond,
一个距离太阳45亿公里的世界 to a world 4.5 billion kilometres from the sun.
冥王星 Pluto.
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