What do the great red spot of Jupiter and the impulses running along your nerves have in common? They're both thought to be examples of solitons — or solitary waves that behave much like particles.
Like so many important scientific concepts, solitons were discovered in a totally random happenstance — in this case, by a Scottish engineer on a horse.
Top image: NASA/Goddard Space Flight Center.
We tend to think of waves as coming one after another, like the rolling waves at the sea shore or the many waves that rip through a cord when it's strummed. This isn't always the case. Sometimes, just one huge curve can travel through a medium, all by itself.
Many people have seen this happen, but it wasn't until the early 1800s that someone bothered to document it. John Scott Russell was going along a channel of water when he saw 'a rounded, smooth, and well-defined heap of water' heading down the channel beside him. For most of us, that would have been the end of the story, but Russell had a horse and the will to use it, and so he gave chase to the single heap of water, following it down the channel to see how far it would go. He claimed that he 'overtook it still rolling on at a rate of some eight or nine miles an hour.' Some of us would have lost our heads and tried to lasso the thing, but Russell kept going, noting how it slowly diminished before the channel started winding and he lost the water lump.
Back Russel went to his home to study his crafty new opponent. He built a wave tank that he used to study the properties of solitons, using the slightly less science fictional name, 'waves of translation.' Solitons, he learned, move at different speeds depending on their size. If two solitons of different sizes meet, they have the wave property of being able to pass through each other and keep going in opposite directions.
Solitons can be tiny, like the impulses sent out by nerves, or giant, like the space soliton that was shown to have moved through the Earth's ionosphere in 2008.
But the Great Red Spot of Jupiter is thought to be the most prominent soliton of all. Solitons have been shown to move through plasma, and the idea is that a single wave, in a rotating atmosphere, can be spun into a vortex. Although the center of the soliton, and the Spot, is a huge red swirl, it moves through the atmosphere of Jupiter the way a soliton does.
If this is true, then the Spot originated not as a temperature differential or a storm, but as a soliton wave produced by the rotation of the planet itself. More data is needed before scientists can be sure, and unfortunately no one can figure the problem out by simply chasing after the spot on a horse, but perhaps someday we'll know if we're really seeing a soliton when we look up at Jupiter.