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

crash it into the sun?

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

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

rocket into a really big dirty bomb.

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

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

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

it, we miss it.

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

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

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

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

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

the sun and whip around, not crashing.

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

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

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

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

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

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

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

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

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

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

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

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

second backwards.

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

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

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

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

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

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

rocket fuel getting to the sun.

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

would a day be on the sun?