- There's a crime wave sweeping the world right now.

- [Reporter] The troubling trend targeting a key car component.

- [Reporter] Thieves targeting cars for their catalytic converters.

- These thefts that take just minutes to carry out.

- And a thief could remove one from your car in 60 seconds or less.

- You feel violated.

- [Joe] The thieves are on the hunt for something that fetches big bucks on the black market.

- [Reporter] A nearly $7 million theft ring.

- [Reporter] They want the valuable metals inside the converters.

- [Commenter] This would be a very quick way for them to make a quick buck.

- Numbers are absolutely skyrocketing and public officials are scrambling for answers.

- We're trending in the wrong direction.

- And people are getting tired of it.

- This is a growing problem.

There's no excuse for it.

- Turns out, we can blame it all on this.

(universe booming) (gentle curious music) Hey smart people, Joe here.

So back in the '70s, air pollution was out of control.

Many U.S. cities were completely blanketed in smog and people were getting sick, all these warnings about acid rain, and one of the big culprits was car exhaust.

So the U.S. passed these huge new environmental laws like the Clean Air Act, which led to one of the most monumental innovations ever in cleaning up the way that we drive: the catalytic converter.

A catalytic converter is basically an extra little chamber along your car's exhaust pipe.

EV owners, this doesn't apply to you.

This magical little box takes dangerous chemicals in engine exhaust and transforms them into relatively harmless gasses that are better for the environment and public health.

I mean, car exhaust still causes global warming, but at least this solved that whole smog thing.

But in recent years, catalytic converters have become one of the most stolen items on cars.

Thefts have risen almost 4,000% since 2018, and numbers are still on the rise.

And that's all because of what's inside.

That little thing on your exhaust that you've probably never looked at is a literal treasure chest full of valuable metals: platinum, palladium, and this one.

Rhodium.

The most expensive metal on planet Earth.

But why do we need this crazy expensive metal in something that cleans literally the dirtiest stuff that comes out of your car?

Well, because of the very unique chemistry that happens inside of a catalytic converter.

Rhodium belongs to a family of metals that are extremely resistant to oxidation and corrosion and heat, so it can stand up to the conditions inside your car's exhaust system and all of the junk that comes through it.

But it also has another super important property: it's a catalyst, which means it can speed up certain chemical reactions.

Here's an example.

Burning gasoline creates harmful chemicals like nitrogen oxides, which can damage the ozone layer, contribute to acid rain, and warm up our planet.

But the rhodium in a catalytic converter turns it into harmless nitrogen and oxygen gas.

And it can do this over, and over, and over again, as long as nobody saws it off your car in the middle of the night.

A catalytic converter has something like a couple of grams of rhodium in it, which has a street value of almost $1,000.

To put this in perspective, right now, a 1kg bar of gold is worth around $57,000.

That's a lot of money.

But that same amount of rhodium would be worth more than half a million dollars.

Here's a little periodic table I have that has actual samples of all of the non-dangerous, non-deadly elements.

This microscopic piece of rhodium I have in here, hold on, we're gonna need to enhance.

Let's grab the macro lens or something.

So this tiny little piece is worth almost $10.

So, why is this stuff so expensive?

When we look at rhodium and its neighbors on the periodic table, we find a lot of stuff that's ridiculously rare, at least in Earth's crust, where we can get to it easily.

If we represent the total of all the elements in Earth's crust by a roll of toilet paper stretching from here to London, rhodium would make up just this much.

To figure out why these precious metals are so rare, we have to talk about how elements are made.

And to understand how elements are made, and where they come from, we have to spend a little bit of time with this.

Every box on the periodic table represents one element, and the type of element you are is determined by the number of protons you have.

If you're an atom with just one proton, you're hydrogen, here at the upper left corner.

If we add a proton, we have element two, helium instead.

Six protons, carbon.

Eight, you're oxygen, and so on.

Protons are positively charged, but like charges repel each other, like identical ends of a magnet.

So why doesn't that repulsion make a nucleus fall apart?

Well, because there's another fundamental force at play inside a nucleus: the nuclear force.

You can think of the nuclear force as velcro that only works when protons or neutrons are pushed very close together.

See, atoms contain both protons and neutrons.

Neutrons also have this sticky nuclear force velcro, but unlike protons, they're uncharged.

They don't repel other stuff.

So neutrons act like an atomic glue that can help hold a nucleus together.

Adding or subtracting neutrons can change an atom's mass, but not what type of element it is.

It's only when we add or take away a proton, along with enough neutrons to keep a nucleus from falling apart, that we make a new chemical element.

And to get protons and neutrons close enough together for that nuclear velcro to do its thing, requires a lot of heat and energy, amounts that we only find in special places and at special times.

The hot, dense universe that existed just after the Big Bang created the perfect conditions to squish protons and neutrons together.

That's how the lightest, most abundant elements on the periodic table were created, stuff like hydrogen and helium.

In fact, all of the hydrogen that exists in the universe was created in those first few minutes after the Big Bang, but to create heavier and heavier nuclei, you need more and more energy.

Unfortunately, the Big Bang only happened once, 13.8 billion years ago, and all of its energy has been spreading out as the universe continues to expand.

So where else can we find enough energy to squish nuclei together?

The fusion reactions that make stars burn turn lighter elements into heavier ones by smashing nuclei together.

Two atoms of hydrogen make one atom of helium.

Smash three helium nuclei together, you get carbon.

Add one more helium nucleus, you get oxygen.

You get the idea.

But cooking up these different elements gets harder as we move down and across the periodic table.

If a nucleus gets big enough, even the immense pressures and energies inside the core of a star aren't enough to keep sticking on new protons.

Turns out iron is the heaviest element that can be made in a star.

So, what about the rest of the periodic table?

Well, everything after uranium was made by humans, but we still need a way to make all of these.

Luckily, there is one more way to add protons to a nucleus: by adding neutrons.

Because neutrons don't have a charge, it takes less energy to get them to stick to a nucleus.

But adding neutrons can also make a nucleus unstable.

That's why radioactive isotopes spontaneously decay, and eject subatomic particles and radiation in the process.

Sometimes, a neutron that's been captured by a nucleus can decay into a proton, and since that's one more proton that wasn't there before, we've created a new element.

If that seems weird and confusing, well, welcome to physics.

This way of adding protons to a nucleus by actually adding neutrons is how most elements on the periodic table are born.

But in this story, every answer seems to bring us to one more problem.

Where do you go to find big piles of neutrons just waiting to get smashed onto nuclei?

So, where do you go to find big piles of neutrons waiting to get smashed onto nuclei?

Well, one place is dying, low mass stars, the ones that don't go out in those violent explosions like their more massive cousins.

They've got lots of free neutrons floating around, so every so often, a nucleus can grab one, it decays into a proton, and becomes a slightly heavier element.

That new element can grab neutron after neutron, some occasionally decaying into protons along the way, forming heavier and heavier elements.

This is a slow process that basically walks box by box along the periodic table, but it takes billions of years for these stars to die, so it's not like they've got anything better to do.

But there's another way to add a bunch of neutrons at once, and one place that we find it is in a supernova, the explosive end of a massive dying star, which is full of free neutrons and a whole bunch of stellar junk.

In the immense energy of a supernova explosion, lots of neutrons can be slapped onto a nucleus at once, before they have time to decay.

Then, when that decay finally does happen, you've effectively added a whole bunch of protons all at once.

So instead of tiny steps, we can take big leaps across the periodic table, and end up with really heavy elements super quick.

We used to think a supernova was the only place that this rapid neutron capture could happen.

Today we know that's not true.

After they collapse and go boom, exploding stars often leave unthinkably dense neutron stars in their wake.

Unsurprisingly, neutron stars are full of neutrons.

And if two neutron stars come close enough together, spiral together, and merge, they release tidal waves of these free neutrons, exactly the ingredients to take those big leaps across the periodic table.

Creating new elements in merging neutron stars used to be purely theoretical, but in recent years, we've actually witnessed these collisions and felt their gravitational aftershocks.

The light given off by one merger 900 million lightyears away, confirmed that heavy elements like gold do form during these violent events, sometimes enough to make ten Earths worth of gold in a single merger.

Is this same process true for rhodium too?

Well, we don't really know, but scientists think that it's likely colliding neutron stars could, in fact, be where most of the heavy metal end of the periodic table is born.

But there's still much about these processes that scientists don't fully understand.

Rhodium and some of its rare neighbors, they likely form in other ways too, perhaps somewhere in between these rapid and slow processes.

But even in a universe that's experienced several generations of dying stars across nearly 14 billion years of existence, these explosive atomic nurseries are rare and pretty spread out.

Across the universe, elements made in these processes are about a million times more scarce than elements like carbon and oxygen.

So, that's why this strange crime wave has taken over, and why people are sawing catalytic converters off of your Prius.

There's just not very much rhodium anywhere because the universe is a really big place.

Two neutron stars colliding and spewing all of their heavy metals into space is like putting a drop of ink in the ocean.

The cloud of stellar dust that condensed into our solar system, and eventually, this little rocky planet, well, that was like taking a bucket of that ocean and making a whole world from it.

Maybe in the future, as car technology evolves, catalytic converters filled with the most expensive substances on Earth won't even be a thing, but for now, this is one crime wave that you can blame on the universe.

Stay curious.