and we don't really know what to do with it. So why don't we just send it into space and

而我們還真的不知道要怎麼處理它。 所以我們為什麼不乾脆把它射離地球，

crash it into the sun?

然後讓它在太陽墜毀？

Well, first, it's really dangerous to put nuclear waste on a rocket, since rockets have

呃，首先，把核廢料放進火箭裡面真的非常危險，

a tendency to occasionally explode while launching, making any nuclear-waste-filled exploding

因為火箭偶爾會在升空時爆炸， 而載滿核廢料的火箭一旦爆炸，

rocket into a really big dirty bomb.

就會成為一顆非常大的髒彈。

But the bigger reason is that it's actually really really hard to *get* to the sun. It

但是更重要的原因是因為要「抵達」太陽 真的非常非常難。

might seem like it should be easy, since the sun's gravity is always pulling us towards

這看來似乎沒有那麼難， 因為太陽的重力總是不斷將我們拉向它；

it. But we're also orbiting really fast sideways around the sun, so that as we fall towards

但是我們繞著太陽轉的速度太快了， 實際上我們會在掉向太陽的同時偏離它。

it, we miss it.

但是我們繞著太陽轉的速度太快了， 實際上我們會在掉向太陽的同時偏離它。

In order to crash _into_ the sun, you have to slow down so that you're _not_ going sideways

為了要墜落到太陽上， 你要降低繞著太陽轉的速度才行。

really fast. The earth - and everything on it - is moving around the sun at around 30

地球──以及上面的所有東西── 大約以每秒30公里的速度繞太陽公轉，

kilometers per second, so you'd have to accelerate to a speed of 30kilometers per second backwards

所以你必須要朝與地球公轉相反的方向 加速到每秒30公里

away from the earth in order to stop moving around the sun and do a sun dive. And you

以抵銷地球公轉的速度，才能墜落到太陽上。

have to slow down all the way – with even a little bit of sideways speed, you'll miss

你得完全減速到零─即使一點點側向速度，

the sun and whip around, not crashing.

都會導致錯過太陽並繞行它，而非墜落。

Ok, so a speed of 30 kilometers per second is really fast, but just how fast? Well, from

好，秒速30公里很快，但到底多快？

earths's orbit, you only need to be going _11_ kilometers per second faster than the

從地球軌道上，你只需比地球公轉速度快每秒十一公里

earth in order to escape from the entire solar system. Which means that it's much, much harder

便能脫離整個太陽系。也就是想墜落太陽

to crash into the sun than to escape it altogether. Let me say that again: it takes less acceleration

比逃離它要難多了。重申一次：前往「其他恆星」

to get to _other_ stars than it does to get to our own sun. Crazy.

所需的加速度比前往自家的太陽少。太狂了。

But it gets weirder: because the gravity from an object is stronger the closer you are to

還有更怪的：因為你離物體越近則引力越強，

it, the smaller your orbit is, the faster your orbital speed. For example, Mercury goes

環繞的軌道越小，則環繞速度需越快。例如水星

around the sun at a speed one and a half times faster than earth, while Pluto goes only a

公轉速度約是地球的一倍半，而冥王星的速度

sixth as fast. And that means it's actually way harder to crash into the sun from Mercury

僅約六分之一。意味著從水星墜入太陽

than from the earth, even though you're closer, because you'd have to accelerate to a speed

遠比從地球難，雖說水星離太陽更近。因為你得加速到

of 48 kilometers per second backwards instead of 30. And it's way _easier_ to crash into

每秒向後48公里，而非30公里。而從冥王星撞太陽

the sun from Pluto, since you only have to accelerate to a speed of five kilometers per

則簡單很多，你只需要加速到每秒向後5公里。

second backwards.

則簡單很多，你只需要加速到每秒向後5公里。

In fact, if you're trying to crash into the sun just using rockets, it's far more efficient

事實上，若你想單靠火箭墜向太陽，更有效率的作法是

to first go to the outer solar system where your speed is much lower, then do a second

先前往外太陽系讓公轉速度減慢，然後點火第二次

burn to counteract that slow orbital speed and allow you to fall directly into the sun.

來抵銷較慢的公轉速度，讓你直接掉向太陽。

And that's precisely why early mission trajectories for NASA's spacecraft to study the sun proposed

這就是為什麼NASA早期的太陽研究任務

going out to Jupiter first – to make it easier to slow down and get to the sun. Ultimately

打算先去木星─為了更快減速前往太陽。

they decided instead to use repeated flyby's of Venus to slow down the probe and save on

最後他們決定讓探測器重複飛越金星

rocket fuel getting to the sun.

來減速，以節省燃料，

But how gravity assists work is a topic for another day. Speaking of which – how long

但關於重力助推的運作原理就改天再談吧。話說回來，

would a day be on the sun?

太陽表面的一天有多長啊？