At the beginning of our poetry class, back when the county jail was still admitting volunteers, two men read some poems they’d written together. 

The first was a love poem – the gist was that any relationship that could survive a partner’s incarceration could probably survive anything. 

The second was a poem about living in a trailer park:

If you’re looking for drugs – not just grass –

Depends where you look, you’ll pro’lly find glass

Pitbulls in the back

Nine times outta ten you’re already in a trap

As it happens, I already knew that one of the authors had a pack of five chihuahuas that road around town in his backpack.  After they finished reading, I mentioned the dogs.

The other guy answered: “Well, yeah, he has those chihuahuas, but I’ve got two pitpulls.”

After we finished talking about their poems, they had a question for me:

“Hey, so you’re a scientist, right?  Cause I heard there’s like this planet where diamonds rain from the sky.  Do you know anything about that?”

I said it sounded ridiculous.  I was imagining walking through a field and suddenly getting hit on the head by a diamond.  Like a really hard hailstone.

Whenever hail falls, my children dart outside to eat ice.  But a fallen diamond would break your teeth.  Doesn’t melt in your mouth or your hand!

During class, we spent a while talking about how diamonds form.  Under extremely high pressure, the hydrogen atoms in an organic molecule can be displaced by carbon-carbon bonds.  There are a few different shapes that work for a molecule made entirely of carbon.  You can have all the atoms in a flat sheet, which we call graphite.  The atoms can form spheres, which we can buckeyballs.  A length of graphite can wrap between the two round caps of a buckeyball.  Or you can have the atoms in a tetrahedral lattice – a diamond.

If you squeeze carbon atoms under really high pressure, you can turn any of the other shapes into diamonds.  Diamonds are the most stable form.  You can make diamonds just by compressing natural gas.

“This pencil, the part it writes with is graphite,” I said.  “If you were strong enough, you could squeeze it until it was a diamond.  But I don’t think they’d fall like rain.”

#

I was wrong.  I was biased about what planets should look like – I live on a small, rocky ball with a thin atmosphere, very different from the gas giants that broil like miniature stars – and biased, unfortunately, against the people who wind up in jail.  I study chemistry, I big expert!

Obviously, there are many occasions when the other people in class know things that I do not.  About poetry, chemistry, and physics.

#

Since 1981, computer models have shown that the extreme heat and pressure deep inside Neptune was likely to create diamonds.  If I’d ever taken an astronomy course – or had borrowed library books about our solar system when I was growing up, instead of reading the same book about Godzilla movies over and over – I could have known this, too.

The sky on Neptune is very different from the sky on Earth.  Our air hugs us with a pressure of about fifteen pounds per square inch.  Deep inside the clouds of Neptune, though, the air would squeeze you six million times tighter.  Needless to say, you’d be crushed.  Parts of you might compress into diamond. 

Temperature is a measure of how fast molecules are moving.  Hot air bumps into you more often than cold air, and each collision is a little harder.

Deep in the clouds of Neptune, the gravity is so strong that air molecules accelerate dangerously fast between every collision.  This means the air is really, really hot – thousands of degrees.  Any parts of you that weren’t being compressed into diamond would melt, or wisp away into the broiling clouds.

The high temperature means there’s plenty of energy available for chemical reactions, so molecules can adopt their most stable configurations even if there is a high “activation barrier.” 

An activation barrier is like a wall that separates a thing from what it wants.  Maybe you’d like to eat breakfast but dread the thought of leaving your warm bed – that’s an activation barrier, too.  We could make the activation barrier lower by yanking your blankets off, which makes your current circumstance worse.  Or we could increase your odds of overcoming the activation barrier by pumping you full of caffeine.  With more jittery energy, maybe you’d get up on your own. 

The second strategy – caffeine! – is roughly what happens when you raise the temperature of a chemical reaction.  Carbon is very stable once it becomes a diamond, but it’s difficult for methane to slough off the warm security of all those bonds to hydrogen atoms.

After methane on Neptune is compressed to form a diamond, the diamond will fall.  A diamond is more dense than the air around it.  But the diamond won’t hit the ground like hail, because there’s no ground beneath the hot dense sky of Neptune.  Instead the rocky core seems to be covered by a superheated ocean – well above its boiling point, but still not evaporating because the liquid is kept in place by dense clouds.  Roughly the same way an Instant Pot uses high pressure to cook food in superheated water.

When the diamonds splash into this ocean, they melt.

#

In class that day, I hadn’t yet researched Neptune’s atmosphere. I was mostly scribbling crude schematics of crystal structures. I explained how to read a phase diagram.  We talked about diamond mining and the technology used to create synthetics.

I claimed, incorrectly, that diamonds weren’t likely to fall from the sky.

One of the guys shook his head.

“I mean, yeah, that sounds all smart and all, but I swear I heard this thing about diamond rain.  Can you look it up before next week?”

The guys in jail can pay to use iPads – at a rate of five or ten cents per minute – but they have very limited access to the Internet.  There’s one un-blocked application with some scientific lectures, but that’s very different from being allowed to learn what you want.

So I agreed.  It sounded ridiculous to me, but I jotted “SKY DIAMONDS?” and promised to do some research.

#

The next week, I was ready to deliver my big mea culpa.  But when I got there, we were missing one of the guys who’d been invested in our discussion.  I asked about him.

“Yeah, he’s not coming back,” said the guy sitting next to me.  “Somebody said he was a cho-mo.”

“Oh,” I said, grimacing.  “He went to seg?”

“Yeah,” said the guy, nodding. We left unsaid that this man probably got the shit kicked out of him first.  If somebody convincingly claims that you’re locked up on a child molestation case, bad things happen.  In prison, you might get murdered by a gang looking to bolster their reputation – because child molesters have such a toxic reputation, there are less likely to be reprisals.  And even a county jail can be a violent place.

After the first fight, the guy who got beaten up will usually choose to go to seg.  Segregation, or solitary confinement, is known to cause permanent brain damage – people suffer from depression, anxiety, and hallucinations.  But staying in a cell block with thirty people who want to kick the shit out of you is likely to lead to brain damage, too.

Solitary confinement might be the less bad of two terrible options.

Despite his bias, the guy I was talking to offered a little sympathy.

“It’s rough,” he said.  “But them’s the politics of the place.”