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Pressure can make us do some pretty weird things, from forgetting our own names during
a big presentation, to giving ridiculous responses to Family Feud categories.
But it doesn’t just make us kick our brains around the floor; pressure causes all kinds
of matter to go through identity crises - like when a lump of flaky graphite changes into
a diamond, the hardest naturally-occurring substance on Earth.
And under extreme pressure, things get even weirder.
Through personal experience or a basic chemistry class, you’ve probably learned that, on
their own, oil and water don’t mix because the water molecules are way more attracted
to each other than to the oil.
But it turns out that under the right conditions, they do mix.
One of those conditions is a whole lot of pressure, which scientists can produce using
a device called a Diamond Anvil Cell, or DAC, which squeezes things between the tips of
two flawless diamonds.
Depending on the force exerted over that teeny tiny experiment area, DACs can produce as
much pressure as what you’d find at the Earth’s core!
In a study published this year in the journal Science Advances, researchers used a DAC to
combine water and liquid methane, or one carbon bonded to four hydrogens.
In a chemistry sense, liquid methane acts like the simplest possible oil.
And at room temperature, the researchers got the two liquids to mix when the pressure reached
2 gigapascals, or almost 20,000 times the air pressure at sea level.
The researchers suggested the compounds could mix because the methane molecules got compressed
to the point where they could slip into the network of bonds connecting all the water
molecules, and distribute themselves evenly.
There’s methane and water all over the solar system, including inside planets and moons,
where the pressure can be super high.
So studying how they react under extreme conditions in the lab can help us learn more about the
chemistry going on in places it’s often impossible to visit.
Oil and water aren’t the only things that play nice under extreme pressures, though.
The noble gases do, too.
Normally, atoms react with each other to get a full outer shell of electrons, because that’s
when they’re the most stable.
Noble gases are elements that already have that shell filled, so unless they lose an
electron, they don’t need to interact with anything — and it’s very hard to force
them to.
Still, compounds with noble gases in them can be useful, like for removing the electrons
from an atom.
But unless they’re in an extreme environment, their existence is usually fleeting.
A lot of the time, you need to use really high pressures to create these compounds — especially
the ones that don’t rely on super low temperatures, or that involve the extra inert elements
neon or helium.
In a paper published in Nature Chemistry this year, researchers created a brand-new helium
compound called sodium helide, which is one helium and two sodium atoms.
It was formed inside a DAC at 113 gigapascals – about as much pressure as just outside
the Earth’s outer core.
The crystal structure of this compound is especially cool, because the helium and sodium
atoms didn’t just link up like in most molecules.
Instead, the pressure arranged the helium and sodium into a kind of 3-D checkerboard
pattern, forcing pairs of electrons to separate and basically hang out on their own in between
the helium atoms, almost like a negatively charged ion without a nucleus.
According to computer models, sodium helide should be stable up to a thousand gigapascals,
which is what you’d find deep inside large gas giants and stars.
That doesn’t necessarily mean there are a bunch of exotic noble gas compounds inside
Jupiter or Saturn, but with more research we might be able to figure out that out.
Now, there is one weird thing that scientists are far more confident exists inside those
gas giants: non-metal elements that behave like metals and conduct electricity.
An electric current is just a flow of electrons.
And for electrons to start moving, they need to have the right amount of energy to leave
their parent atoms and join what’s basically a sea of moving electrons.
Some elements, like metals, have outer electrons that come by this energy super easily, so
they’re good at conducting an electric charge.
The electrons in insulators, on the other hand, have a tough time getting enough energy
to break free and flow.
Most nonmetals are insulators.
But at high enough pressures, the atoms can get squeezed into creating that communal sea
of electrons, and the insulator becomes conductive.
That’s exactly what happens inside Jupiter.
If you were to plunge straight down through Jupiter’s atmosphere, you’d quickly get
crushed to death like the Galileo probe before you.
Oops.
But if you somehow made it around a third of the way down, where the pressure is more
than 100 gigapascals, you’d find metallic hydrogen, which continues all the way to the
core.
Astronomers think this conductive fluid is what gives Jupiter its super strong magnetic
field.
The effects of high pressure can also work in reverse, causing some metals to lose conductivity
or become insulators.
In those cases, the increased pressure changes the solid metal’s overall structure, locking
the electrons up between atoms so they can’t flow freely.
So, all kinds of strange things can happen under extreme pressure.
And by studying them, we keep finding more ways the usual rules of chemistry and physics
don’t apply.
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