You're Technically HOTTER Than The Sun (with XKCD!)

Spoiler alert: this won't end well.

There are five large worlds that share names with chemical elements: the planets Mercury,

Uranus, and Neptune, and the dwarf planets Ceres and Pluto.

What if - 2 have some fun - each world suddenly became composed of

its corresponding element?

Mercury and cerium are metals,

so Mercury and Ceres would mostly just get slightly heavier and shinier.

From earth they'd look a bit brighter in the night sky,

enough that Ceres would become visible to the naked eye.

Unfortunately, the night sky - and human eyes - would get a little harder to find,

thanks to the other planets.

Plutonium, uranium and neptunium are radioactive;

plutonium and uranium do have (non-fissile) isotopes

which decay slowly and mainly produce a bit of heat.

A small lump of Uranium’s most common

and stable isotope wouldn’t even be hot to the touch.

But if you collected it into a planet-size ball,

the tiny amount of heat produced by each part would add up to heat

up the planet to thousands of degrees.

* It might seem strange

that something that's cool in small amounts would be hot

when collected together in a big ball,

but this is just a consequence of geometry and the physics of radiating heat.

Since volume grows faster than surface area,

and the volume is where the heat is produced,

the interiors of large heat-producing objects produce more heat relative to their surface areas.

But thermodynamics doesn't allow objects to just radiate more heat - they have to

get hotter to do

so;

the hotter they are, the more heat they're allowed to radiate.

So a large heat-producing object will produce more heat than it can radiate away

until that heat builds up (enough)

and the object gets hot - hot enough

that it can radiate away enough heat.

Really big objects can get extremely hot from just a tiny amount of heat

production per unit of volume.

Like, the Sun.

A cup of the sun's core * produces about 60 milliwatts of thermal energy.

By volume, that’s about the same heat production rate

as the body of a lizard,

and substantially less than that of a human.

In a sense, you are hotter than the Sun—there’s just not

as much of you.

But we were talking about Uranus, which there is a lot of,

and which would get really really hot if made from uranium.

The real Uranus, lit by the sun,

is too dim to see with the naked eye.

But the superhot uranium Uranus would glow bright enough to be visible like an

ordinary star in the night sky.

And plutonium Pluto would heat up

and glow enough that from earth it would also be visible to the naked

eye - though just barely.

Except you wouldn't be spending much time looking at the night sky anymore,

thanks to neptunium Neptune.

Even the most stable neptunium isotope is fissile,

so 237Neptune would instantly undergo a runaway fission chain reaction,

converting the planet into an expanding cloud of high-energy particles and X-rays.

Around four hours later, the shock wave would reach—and completely obliterate—the Earth,

stripping away its surface and everything on it and leaving behind a molten blob.

We'd have gotten similar results for Uranus

and Pluto if we'd instead used fissile isotopes of uranium

or plutonium,

though as a bonus Uranus' shock wave would reach

(and destroy) us about an hour faster than Neptune's.

There's a simple takeaway from all this:

If you have a choice between isotopes

and you’re not sure

which to pick,

go for the most stable one.

And just stay away from neptunium altogether.

Ok - I'll avoid neptunium.

But what if to be silly we filled the solar system with soup out

to Jupiter?

Or what if to pass the time we spun the earth up

so that a day lasted a second?

Or what if to avoid getting in trouble you tried to read every single

law that applies to you?

What if to answer these questions you could just read a book called What

if 2,

that this video is based on and supported by?

What if two reasons to read what

if 2 are that it was written by Randall Munroe

and that it has over 60 answers to important "what

if" questions like "what

if Japan disappeared?"

What if to read what

if 2 you just had to look at the information in the description of

this video?

What if two be clear, is available wherever books are sold,

and when you get yourself a copy, then you can ask "what if," too.