行星（2019）

A difference of just four degrees Celsius
就足以让热量向上升腾
is enough for the heat to radiate up
使冻结的氮蒸发形成气体
and vaporise the frozen nitrogen, creating gas.
气体在压力下最终冲破了氮冰
That gas is under pressure, and, ultimately,
裹挟着深色物质上升
it punches through the nitrogen ice
这也就形成了海卫一上面的间歇泉现象
carrying those dark particles up and making the geysers of Triton.
在太阳系这个最偏僻的角落
In the furthest reaches of the solar system,
阳光即便微弱 也足以产生力量 创造出这番
the faint light of the Sun is still enough to power the most
距离最遥远的地质奇观
distant of geological wonders.
不过这并不能完全解释海卫一的其它神秘特征
But this can't explain the rest of Triton's mysterious features.
表面覆盖数千个裂缝和凹坑
如此显著的地形特征 只可能是由
Terrain on this scale could only be created
一股更强大的力量创造的
by a much more powerful force.
线索似乎藏在海卫一奇特的运行轨道中
And a clue seems to be lurking in Triton's odd orbit.
不同于太阳系所有其它大个卫星
Unlike every other large moon in the solar system,
海卫一的公转方向与海王星的自转方向是相反的
Triton orbits in the opposite direction to the spin of the planet.
这说明海卫一和海王星
And that means it's highly unlikely
不太可能是同时形成的
that Triton and Neptune formed at the same time.
如果行星和它的卫星形成于同一片塌缩的气体尘埃云
If you formed a planet and a moon out of the same collapsing cloud
它们的自转和公转方向往住是一样的
of gas and dust, then they tend to spin and orbit in the same
与最初的尘埃云旋转方向相同
direction as the spin of the initial dust cloud,
所以最有可能的解释是 海卫一是海王星系统的
so, the most likely explanation for that is that Triton is a visitor
一个访客 不过没像“旅行者”2号♥一样再离开
to the Neptunian system, that, unlike Voyager, never left.
太阳系外♥围♥
一种理论认为 数十亿年前
One theory is that, billions of years ago,
海卫一并不是一颗卫星
Triton was not a moon at all.
它成长于海王星之外的一个区域
It grew up in a region of space way beyond Neptune...
这就是柯伊伯带
..the Kuiper belt.
在这里 数万亿由水 氨和甲烷
Here, trillions of frozen lumps of water, ammonia
组成的冰体环绕着太阳
and methane circle the Sun.
它们是太阳系形成时的冰残留物
The frozen leftovers from the formation of the solar system.
或许海卫一后来来到了这个区域的内缘
Perhaps Triton ended up on the inner edge of this region...
然后由于足够靠近海王星
..and ventured close enough
导致被引力捕获
to Neptune to be drawn in by its gravity...
直到它最终被拉出柯伊伯带
..until, eventually, it was plucked from the Kuiper belt,
永远被困在了这个遥远蓝色行星的轨道里
and forever trapped in orbit around the distant, blue planet.
如今海卫一围绕海王星公转的轨道是一个十分规整的圆圈
Today, Triton orbits in a nice, regular circle around Neptune,
不过它的轨道最初并不是这样的
but it wouldn't have started out that way.
海卫一刚刚被捕获时 它应该是掠过了海王星
When it was first captured, it would have glanced
然后沿一个椭圆形轨道运行
past the planet and ended up in a wide, elliptical orbit,
有时候离海王星很远 有时候很近
sometimes being far away from the planet, and sometimes close.
这意味着在海卫一围绕海王星公转的过程中
That means that, as Triton orbited around Neptune,
万有引力是不断变化的
the gravitational pull was constantly changing,
它一直拉拽 碾压海卫一 并通过摩擦
and that stretches and squashes the moon, and heats up
使其内部温度上升
the interior by friction.
这个过程叫作潮汐加热
It's a process called tidal heating.
炽热的内部物质很可能通过海卫一外壳上的
The molten interior would have exploded up through cracks
裂缝和断层喷发出来
and faults in Triton's crust...
形成了我们今天看到的凹凸不平的表面
..creating the ragged surface we see today.
现在剩下的就是一个冷却下来的卫星
And what you're left with is a cooling moon,
公转轨道为圆形 方向与行星自转方向相反
orbiting in a circle the wrong way around the planet,
它过去的动荡不得而见
the dramas of its past hidden from view.
保留下来的只有那些间歇泉 微弱的太阳光为它们提供能量
All that remains are the geysers, powered by the faint light
在如今沉寂的海王星表面留下了一道道深色纹路
of the Sun, painting dark streaks across the now-quiescent surface.
“旅行者”2号♥已经完成了它的使命
Voyager had fulfilled its mission,
现在它继续前进 准备飞出太阳系
and now headed onwards, out of the solar system...
它将不会再遇到另一颗行星了
..where it would never encounter another planet.
不过在别处 另一个世界正等着我们到访
But, elsewhere, another world awaited our arrival...
一个更加深入黑暗的世界
..far out in the darkness.
我们已经点火并发射了美国国家航♥空♥航♥天♥局的“新视野”号♥探测器
Mission... And lift off of Nasa's New Horizons spacecraft
它将在10年的漫长航行后 造访“行星”冥王星 然后继续前进
on a decade-long voyage to visit the planet Pluto and then beyond.
“新视野”号♥ 2006年
迄今发射速度最快的探测器
“新视野”号♥
The New Horizons spacecraft,
踏上了前往太阳系最边缘的旅程
on its way to the very edge of our solar system.
前往冥王星飞行时间 9.5年
人类想要了解这个奇妙小世界的雄心能否实观
Our ambition to learn more about a small,
取决于“新视野”号♥能否成功完成航行
intriguing world depended on the success of New Horizons.
这个长度不到3米的小探测器
As the tiny probe, less than three metres in length,
被送进了宇宙深渊
was sent out into the abyss...
它的大部分电子器件和所有非必要系统
..most of its electronics and all nonessential systems
都为了节约电力而关闭了
were shut down to save power.
它将在全长48亿公里的航程中 几乎一直处于休眠状态
It would hibernate for almost its entire 4.8 billion kilometre trek.
就在“新视野”号♥持续飞向冥王星的同时
Whilst New Horizons continued its voyage to Pluto,
地球上发生了一场关于冥王星定义
a controversy arose here on Earth about the definition
的争论
of Pluto itself.
我们过去一直都知道冥王星很小
See, we always knew that Pluto is small,
比海王星的卫星海卫一还要小 但直到哈勃空间望远镜
smaller than Neptune's moon Triton, but it was discoveries made
在冥王星附近有了新的发现之后
in the vicinity of Pluto by the Hubble Space Telescope
它的行星地位才真正受到了挑战
that really challenged its status as a planet.
从地球上看 远在柯伊伯带内缘的冥王星
From Earth, Pluto, far away on the inner edge of the Kuiper belt,
由于距离过于遥远 即使用哈勃望远镜
is so distant that, even with Hubble, it appears
也只能看到一个模糊的图像
as nothing more than a fuzzy image.
但冥王星并不孤单
But Pluto was not alone.
我们开始探测到其它遥远的天体
We began to detect other distant objects.
夸欧尔 发现于2002年
塞德娜 发现于2003年
妊神星 发现于2003年
鸟神星 发现于2005年
之后哈勃望远镜又发现了一个
Then, Hubble discovered that another world
几乎与冥王星同等大小的天体
is almost the same size as Pluto.
阋神星 直径2326公里
这些新发现的天体 让人们不得不重新思考
The discovery of these new worlds has forced us to reconsider
“行星”这个词的含义
what we mean by the word "planet".
国际天文学♥联♥合会对行星的定义包括三点
The International Astronomical Union has a three-part definition
第一 它必须围绕太阳公转
of a planet. Firstly, it has to orbit the Sun,
冥王星确实如此
and Pluto certainly does that.
它每248年公转一次
It goes round once every 248 years.
第二 它必须质量足够大 好让它在引力作用下
Secondly, it has to be massive enough for gravity to sculpt it
变成近似球形的形状 而冥王星基本也是一个球形
almost into a sphere, and Pluto indeed is almost spherical.
第二 它围绕太阳运行的轨道上不能有障碍物
But, thirdly, it has to clear its own orbit around the Sun,
这其实也是对质量的要求
and that's essentially a mass constraint as well.
它必须有足够大的引力来清除
It has to have enough gravity to throw things out
公转轨道上的天体
from its orbital path.
而冥王星并不符合这样的要求
And that's where Pluto falls down.
那么为什么要加上这一条呢
Now, why that extra idea?
说到底这是因为 如果冥王星大到足够成为一颗行星
Well, ultimately, it's because if Pluto is big enough
那么就体积而言阋神星也是行星
to be a planet, then Eris is big enough to be a planet,
鸟神星也是一样的情况
and Makemake is big enough to be a planet,
数十个 甚至数百个足够大的天体
and tens or even potentially hundreds of objects out there
都有可能成为行星
are big enough to be planets.
所以这个条件真的那么重要吗
Now, does it really matter?
我并不这么认为
Well, I don't think so.
冥王星终究还是一个天体 因此我们应该去探索它
Ultimately, Pluto is a world, and, therefore, we should explore it.
准备 1 2
这正是我们在2015年7月采取的行动
And, in July 2015, that's exactly what we did.
准备 中心平台
经过9年的飞行 “新视野”号♥被唤醒
After nine years of flight, New Horizons awoke.
收到
Copy that.
我们正与太空营进行遥感对接
We are locked by telemetry with the phase path.
冥王星 距离太阳59亿公里
我们第一次瞥见人类探测过的最遥远的星球
We had our first glimpse of the most distant world ever visited.
克苏鲁斑 3000公里宽的黑暗地带
超过5000个撞击坑
光晕状撞击坑 维加台地区域
光晕状撞击坑 维加台地区域
（最大的撞击坑 50公里宽）
丹增山脉 最高峰高达6公里
冥王星十分美丽
Pluto is beautiful.
它完全不是一个冰冷的 毫无特色的星球
And, far from being a frigid, featureless world,
事实证明 一颗充满活力的行星
it turns out that it has all the characteristics
该有的特色它全部具备
of a dynamic, living planet.
没错 它的表面很冷 大约零下230摄氏度
And, yes, it is cold on the surface, about -230 degrees Celsius.
行走其上 脚下是坚硬的氮冰
I'd be walking over solid nitrogen.
而在哈勃空间望远镜
But the blotches that could be made out
模糊的图像上显示为黑斑的区域
in the grainy Hubble Space Telescope images turned out to be
其实是及其丰富多样的地质形态和结构
a tremendous variety of geological form and structure.
不过到目前为止辨识度最高的特征是一个叫作
But by far the most recognisable feature is the region known
汤博区的区域
as Tombaugh Regio,
它有一个更为人所熟悉的名字 冥王星之心
or to give it its more popular name, Pluto's Heart.