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.

8 00:00:22,610 --> 00:00:24,990 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."