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Earth has its share of monster storms,
but even the most powerful hurricanes
are a breeze compared to the great planet-sized tempests
of the gas giants.
The great vortices of the Jovian planets
are true storms, analogous in many ways
to Earth's hurricanes.
But there are, of course, some differences.
For example, these storms are as big as entire planets.
The largest and oldest storm in the solar system
is Jupiter's Great Red Spot, stretching
an incredible two to three times the diameter of the planet
Earth.
Meanwhile, the fastest winds ever
measured, clocking 1,500 miles per hour, once raged
in Neptune's Great Dark Spot.
Saturn's polar vortex is a 20,000-mile-wide monster shaped
like a hexagon.
Even plain-looking Uranus hides USA-sized hurricanes
below its methane haze.
There are many unsolved mystery surrounding these epic storms.
We may be close to finding some answers following
the Juno spacecraft's recent flyby of Jupiter's Great Red
Spot.
Before we get to the unknown, let's talk about what we do
know about these storms.
In fact, let's start with those found on Earth.
Hurricanes, cyclones, and typhoons
are all the same weather pattern.
Their name just depends on where they form.
As with the gas giant storms, these monsters
are powered by convection.
Warm water-laden air rises from below,
while cool air and precipitation sink from above, creating
a vertical convection cell.
In the case of earth storms, the energy powering that convection
comes from the sun-warmed ocean.
This convection sustains a central low-pressure region,
which sucks in the surrounding moist ocean air.
These incoming winds travel such large distances
across the Earth's surface that they are
subject to the Coriolis force.
Earth is, of course, rotating on its axis.
Any object moving over a spinning surface
will appear to follow a curved path relative to an observer
moving with that surface.
On a clockwise-spinning surface, there's
a pull, a Coriolis force, to the left,
while on a counter-clockwise surface
the Coriolis force is to the right.
So as air rushes in all directions
into a low-pressure storm cell, the Coriolis effect
causes it to curl around in a circle.
The result is a raging vortex in the same direction
as the Earth's rotation, clockwise
in the southern hemisphere and counterclockwise in the north.
These storms can persist as long as the warm ocean provides
energy to drive the convection cycle.
Over cold water or land, this power source is cut off
and the storm dies.
Another key to hurricane's longevity is moisture supply.
Wet ocean air is pulled in by the low-pressure core,
and it rises in the convection cell.
As it cools, it condenses into clouds,
which are driven outwards.
Eventually, the moisture rains down, completing the cycle
and maintaining the storm's core.
This is another reason why storms weaken near or on land.
Too little water, and convection ceases.
It's also why the most powerful storms
are driven by low-pressure rather
than high-pressure cores.
See, a low pressure core draws inwards,
replenishing the water supply.
A high-pressure core pushes air outwards,
depleting the supply of moisture and shortening
the storm's life.
The outgoing winds of a high-pressure cell
still do respond to the Coriolis force, so they form a vortex.
However, that vortex rotates in the opposite direction,
clockwise in the north and counterclockwise in the south.
Whereas low-pressure vortices are called cyclonic,
high-pressure vortices are called anti-cyclonic.
So there we have it.
The most powerful storms tend to be
low-pressure cyclonic systems powered by sun-warmed water.
Gas giant storms are a little different.
They are most often anti-cyclonic, high-pressure
systems and are powered not by the sun,
but by the collapse of the planet itself.
See, the planet's never quite finished forming.
They originally collapsed from the vast gas disk left over
after the sun's birth.
But five billion years later, that collapse
continues, albeit very slowly.
Jupiter, for example, shrinks by about two centimeters
every year.
As they contract, gas giants convert
gravitational potential energy into heat,
which in turn powers the largest storms in the solar system.
As contraction-heated gas rises, it cools.
On Earth, the only source of condensation is water,
but the gas giants' atmospheres span such a wide range
of temperature and pressure that all sorts of molecular species
condense.
Most of Jupiter's visible clouds are ammonia ice, tainted
with colorful impurities, but there also
clouds of hydrogen sulfide and regular H2O.
The phase changes from gas to liquid to solid release latent
heat that lifts the storm still higher.
All of this happens in the troposphere,
the densest and innermost layer of the atmosphere.
On Earth, the troposphere is about 10 miles thick.
But on the gas giants, it can extend 100 miles
into the planet's murky depths, where pressure forces the gas
into a metallic liquid state.
A powerful storm can breach the tropopause
into the stratosphere.
For example, the Great Red Spot towers eight kilometers
above Jupiter's iconic bright and dark belts.
Now, the spot itself is quite cold, in fact below freezing,
but all of its activity warms the upper atmosphere
to 1,600 Kelvin.
With such a wide range of molecular species
driving an incredibly deep convection cycle,
there's no danger of a Jovian storm system running out
of molecules to condense.
Even high-pressure, outward-blowing storms
don't dry up like they do on Earth.
In fact, all of the famous storms like the Great Red
Spot, Neptune's Great Dark Spot, and Saturn's polar vortex
are or were anti-cyclonic.
Gas giant storms can last for many years.
Neptune's Dark Spot lasted several years
before dissipating in 1994.
However, Jupiter's Great Red Spot
has raged for at least 350 years.
We're still trying to unlock the secrets of these storms'
longevity.
A combination of a near inexhaustible supply of heat
and an abundant supply of condensable molecules helps.
In the case of the Great Red Spot,
it also helps that the beast frequently cannibalizes small
storms, absorbing their energy, and that it is sandwiched
between a pair of 300 to 400-mile-an-hour jet streams
that are moving in opposite directions to each other.
These help keep the spot spun up.
But even with all of this, the Great Red Spot's
centuries-long life span is mysterious.
And in fact, it may finally be coming to an end.
The spot is showing signs of shrinking.
In the 1800s, it spanned 37,000 kilometers,
or about three Earths in width.
However, as of April this year, the spot
spans just 16,350 kilometers, or 1.3 Earths.
The storm is also circularizing.
And although its smaller, its wind speeds haven't diminished.
Is the great red spot fading away?
What's causing this shrinking?
The answers to the storm's longevity and fate
may be found in the details of its structure.
And for that, we need to get close.
For that, we need Juno.
NASA launched the $1.1 billion Juno mission in 2011.
The probe will swing within 3,400 kilometers
of the Jovian cloud tops and ultimately crash into them
to avoid contaminating potentially life-bearing moons
like Europa and to peek under the gas giant's cloud cover.
Juno carries eight instruments, including a radiometer
for probing the atmospherics high-pressure depths,
an imaging spectrograph for studying cloud chemistry,
a magnetometer for measuring Jupiter's
intense magnetic field, and a four-color wide-field JunoCam.
Juno spends most of its orbit millions
of miles away from Jupiter's harsh radiation,
but every 53 days it ducks under the radiation belt
and turns on its instruments for a two-hour transit from pole
to pole.
During that time, Juno snaps a picture every 60 seconds,
fast enough to catch at least six angles of a given feature.
This is perfect for measuring cloud heights
and also to record horizontal cloud drift,
which gives us wind speeds.
Juno's flyby images of the Great Red Spot are really amazing.
These are taken by JunoCam and incredibly
processed by volunteer citizen scientists
Look at the difference between these images
from Hubble, Galileo, Cassini, and Juno.
The level of detail is incredible.
All of these images were taken on July 10
during Juno's seventh flyby from just 5,600 kilometers
above the clouds.
With all the little plumes and eddies,
it is the first time we've seen so many storms
within storms, especially in the Great Red Spot.
They weave around the edges at top speed.
But in the center, everything is perfectly calm like the eye
of a mega-hurricane.
Even accounting for the resolution limits
of older photos, Juno is revealing real changes.
For example, there's a transition
from long streaks to smaller eddies.
This represents a shift from streamline to turbulent flow.
Turbulent flow acts like friction, sapping energy away
from the bulk rotation.
And this may be connected to the spot's shrinking size.
As well as getting smaller, the Great Red Spot
is becoming more circular.
In fact, it may be completely circular
in the next couple of decades.
But that doesn't necessarily mean it's going to vanish.
Besides size, velocity is a good measure of storm strength.
Over the last few decades, the storm has gone smaller,
but it now appears that its winds are not any slower.
The pictures from JunoCam are just the beginning.
Juno's other science instruments have
provided an enormous amount of data,
and more will come in the upcoming 30 flybys.
Scientists are poring over this data right now.
And with the help from citizen scientists,
perhaps like you, we're sure to unravel
some of the secrets of the solar system's most powerful storms.
You could stay updated on Juno's discoveries
on its interactive website and by staying tuned
to "Space Time."
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I want to send out a storm of thank you's
to our Patreon supporters.
You make our job so much easier.
And a very special thanks to quasar supporter Mars Yentur.
Mars, you're hoping us keep the lights on
and the convection cells powered.
Last week, we talked about John Archibald Wheeler's one
electron universe idea as well as
gave the solution to the Feynman diagram challenge.
You guys had a lot to say.
Andreas64 asks why we don't also talk about the one proton
or one neutron universe.
Well, Wheeler was really just using
the electron as an example.
The natural extension would be that every elementary particle
along with its anti-particle counterpart
is the same particle bouncing forwards and backwards in time.
Not too much protons and neutrons,
but the different quarks as well as muons, neutrinos, et cetera.
Keith Gaughan wonders if the imbalance between matter
and anti-matter is due to the time
in the history of the universe that we're observing.
Well, actually, the fun thing about the one electron
proposition is that it doesn't matter when in time you are.
You should always see the same proportion of matter
to anti-matter.
To prove this to yourself, try drawing
a space-time diagram, time on the y-axis and space
on the x-axis.
Now, draw the zigzag of an electron bouncing up and down.
Start moving upwards and end moving downwards.
Make each turning point at a different time
so the zigzags are uneven.
Now, draw some horizontal lines.
Count each upward-moving line as an electron
and the downs as positrons.
It doesn't matter what times you choose.
You'll always get the same number
of electrons versus positrons.
Vacuum Diagrams points out that two diagrams are missing
from the challenge answer.
There should be diagrams with photons connecting
across the vertices of the two-vertex photon deflection
diagram, like this.
My bad.
I incorrectly considered these to be self-energy diagrams.
Fortunately, no one was penalized for my error.
YouTube Account points out that the perfect name for dark flow
isn't WTF flow, but rather what the flow.
Yeah, I realized I'd missed that puntunity right
after leaving the studio.
I was even tempted to reshoot, but thank you
for giving me the chance at redemption.
Don Solaris asks how I manage to make
my beard super-symmetrical.
Well, my barber just shaves half-integer spin off
the sides.
It really takes my facial hair beyond the standard model.