What would be necessary in order for bubbles to rain down from the sky, whether they are actually soap or something else? Would it even be possible?
Aside from a bunch of little kids (which would be awesome to be honest) would there be a natural phenomenon similar to this?
Let's assume for a moment that there are bacteria living in clouds. These have to feed on something, but nutrition in clouds is scarce. The chances of collecting molecules with nutritional value increase with the surface area that can be used to collect them.
Sometime during the endless evolution some bacteria managed to excrete a slimy substance that can trap gas and form a bubble. Additionally, the bacteria excrete a gas as metabolic product which now is trapped inside the bubble, increasing the surface area that catches nutritional molecules.
Due to global warming and rare weather conditions that blow nutritious Sahara dust into those clouds, the bacteria reproduce faster than usual, weighting down their bubbles until they rain down to earth in a spectacle dazzling thousands of people.
Alternate version on an alternate planet (thanks to EngrStudent):
I think that in a methane and nitrogen rich atmosphere, in a space with lots of grains of sand meteors made of iron or nickel, you could superheat methane in the presence of nitrogen and a catalyst, and make more complex compounds. Aerial bacteria could then convert those to "soap" as a protection, and as they emit metabolite gas, make bubbles.
Eucalyptus trees can form bubbles when it rains
Combine a eucalyptus grove with rain and a high wind that blows the bubbles away as soon as they form and you have a rain of bubbles somewhere down the line.
One fun idea would be a new generation of planes.
Explanation : In order to create bubbles in the sky the presence of surfactant molecules are needed. One natural surfactant molecule used in shampoo is called "Decyl glucoside". It is obtained by the reaction of glucose from corn starch with the fatty alcohol decanol which is derived from coconut (wikipedia).
This molecule is an alcohol with a "long" carbonated chain which is not so far from the regular ethanol which can be used as fuel.
Now imagine a new generation of little planes using this molecule as fuel : 100% natural and environmentally friendly. The only thing engineers didn't manage to do was to obtain a complete combustion of the fuel so a small fraction of these molecules are just released in the air.
The unexpected effect has been to see the apparition of rains composed of... Bubbles ! But this is a little cost to pay for an environmentally friendly plane so this technology is now very popular and it rains bubbles on a daily basis.
Raining bubbles is somewhat similar to sea foam. Both require the water (or similar substance) to be stretched and agitated in such a way in which to encircle and trap air. Simply put, our rain here on earth cannot take the form of bubbles because they are so dense and do not have forces placed upon them that would shape them into disks and eventually bubbles. By having very specific air patterns, such as multiple focused streams of air rising upwards from the ground, it is possible to have individual raindrops spread apart and become "injected" with air, forming them into bubbles.
However, air streams such as these do not occur naturally on earth, so you would have to create a reasoning for these air currents to exist in the first place, be it vents, or organisms, or what have you.
Unfortunately, this method is not likely to catch every single rain drop, so a rainstorm would likely contain a mixture of droplets and bubbles.
One possible condition to have bubble rain would be a large differential pressure in one gas across the height of the atmosphere.
Let's say, for the sake of this question, that CO2 has a pressure of 1 bar above 6000 m height, and the usual value we are used to below that height, with the overall atmospheric pressure being 1 bar (let's ignore for the moment the change of pressure with height).
When the rain drop forms it will be saturated in CO2, but upon descending the excess gas will try to get out to accommodate for the different pressure. This will form an air pocket into the drop, generating at all the effects a bubble: a liquid shell around a pocket of gas.
1) Wind formations that lift from the ocean and bring particulate and other light matter into clouds over the land.
2) Regular lightening strikes into the ocean causing:
Dead carcasses of very fatty sealife.
Lye formation (also chlorine formation, but assume the different weights work out such that the wind moves lye and chlorine to different locations).
3) Many birds that gorge on the fatty carcasses and release their excrement into the air where it is then lofted by the winds and brought inland (winds not too strong for the birds to be caught up in).
4) Lye + water vapor + fatty acids = soap.
5) Soap (it's gel at this stage) + more water = diluted liquid soap.
6) Liquid soap + gentle force of forming raindrops + gentle winds = bubbles.
Actually not sure whether this would work, but think of a planet with a very low gravity. This would automatically lead to the water forming more or less sphere("bubble") like shapes.
If you still need a big surface, make your planet have no core. Or, even better, have a Lagrange point at the surface due to another planet - eg the two planets are orbiting each other, such as Pluto and Eris, in such a constellation that objects on the surface are almost equally dragged towards both of them.
However, one planet still has to drag the stronger, else the bubbles would float in air, but not come down...
With such a low impact of gravity, air would be mainly influencing your bubbles.
Example - Water bubble in space, NASA
A different attempt would be magnetic fields. We all know that electromagnetical forces(Couloumb-Force) are far stronger than Gravity. So they can influence the water in such a matter that it forms bubbles.
Example - balloon next to water
And now think of some particles in the air that are charged with a high positive or negative charge. They would get a water bubble around them...
