It's our solar system's most recognizable planetary feature, and it may not exist fifty years from now. Jupiter's great red spot! Everybody's favorite 16,000 kilometer wide, centuries-old storm is full of surprises. From its color to its duration, to stunning recent observations that it may indeed by winding down. 

So much weirdness. But let's start with the origins of what astronomers call the GRS. Scientists think the storm on Jupiter has been raging for at least 400 years and probably longer. Italian astronomer Giovanni Cassini is credited with making the first observations of it in the late 1600s. But researchers say it was probably churning long before he, or anyone else, even knew it was there. But how exactly the storm has lasted so long has baffled scientists for decades.

The GRS is basically a hurricane at least twice the size of Earth. It spins counter-clockwise, with winds at its edges gusting to more than 430 kilometers an hour, and it takes 6 days to complete a single rotation. Here on Earth, the largest storms - tropical cyclones like hurricanes and typhoons - last a few weeks at most before sputtering out. And given our current understanding of fluid dynamics, scientists say the GRS should've disappeared centuries ago. But of course scientists are used to studying storms on Earth and things on Jupiter are just, well, they're pretty different. 

For one thing, Jupiter has no surface. The planet is almost all hydrogen and helium so unlike our world, there aren't any land masses that help break a storm system up. Plus when studying weather on Earth, scientists tend to focus on the horizontal flow of winds like the jet stream or the gulf stream. So for a long time, experts focused on the fact that Jupiter's red spot sits between two enormous currents flowing in opposite directions. 

But new evidence suggests some of the storm's longevity may be caused by vertical wind flows too. Some observers now think that the downward flow of hot gases from above and the upward flow of cold gases from below may also be at work, continually feeding the system with new energy and keeping it going.

But you know what else is weird? The great red spot isn't actually red. For years, scientists assumed the red in the great red spot was caused by phosphorous compounds that are found throughout Jupiter's atmosphere. But NASA's Cassini mission, along with experiments conducted on Earth, have shown that the color more likely stems from the break up of other chemicals in the very top layer of the vortex.

The storm's swirling clouds are probably a mixture of mostly ammonia and hydrocarbon acetylene, and in all likelihood, these clouds are really white and gray. But the top of the GRS stands many kilometers above the clouds around it, and when sunlight hits its highest layer, scientists think that it splits those substances into compounds that produce the spot's signature color. 

In lab experiments, researchers have blasted this combination of gases with UV rays, mimicking the high altitude reactions that occur atop the GRS. And the result was a reddish material with the same color properties as the Jovian red spot. 

And finally, like I said in the beginning, no storm lasts forever. And the fact is the great red spot is shrinking quickly. When astronomers made the first rudimentary measurements of the GRS in the 1800s, they estimated it was more than 40,000 kilometers across. By the time Voyager 1 and 2 made their flybys in the late 1970s, the storm had decreased to about 23,300 kilometers. In 1995, some of the first Hubble images of the GRS measured it at 20,900. And by 2009 it was just 18,000! 

The most recent measurements reveal a storm that's now less than 17,000 kilometers across, and appears to be shrinking by more than 900 kilometers per year. The change is so great that what was once an easily recognizable oval, is slowly morphing into more of a circle. And at this rate, it will be gone in a few decades. 

And since scientists still aren't entirely clear why the storm has lasted so long in the first place, they are hard pressed to explain why it's shrinking. One theory is that small, nearby eddies are feeding off the storm, changing its internal dynamics and sapping its energy. But astronomers also admit that they are just baffled, and that they may be some dynamic going on inside the super storm that'll need a lot more studying to explain. Hopefully it'll last long enough for us to figure it out. 

In the meantime, you might as well go take a look at it before it's gone. Thanks for watching SciShow Space, and especially to our patrons on Patreon who help make this show possible. If you wanna be a part of that, just go to patreon.com/scishow and don't forget to go to youtube.com/scishowspace and subscribe.