We get a lot of rain here in northeast Scotland, but it’s usually the easy stuff: a general weighted mist, tiny water masses that dampen your hair and trousers (and the rest of you, if you forgot a coat). It can be worse, cold and stinging like shards of ice spat at bitter angles, or it can be exuberant: warm, fat droplets that soak to the bone and pool in hoods and sleeve creases and open backpack pockets. It’s usually nothing special; nothing weird.
Rain gets weird. Raindrops form when water vapor in a cloud condenses around a particle like dirt or dust—they’re not pure water. Sometimes they get mixed up with spores and pollen and ash and meteor debris (we think), and the resulting rain can become reddish, white, or green. Red rain, known more commonly and punk-rock-ly as blood rain, has been recorded since Zeus rained red to warn of bloodshed in Homer’s Iliad and Plutarch observed a cosmic punishment of famine and a rain of blood.
Blood-like streams coursing toward storm drains and milky puddles dripping from wide leaves are unsettling, but rain gets weirder still. Strong winds and tornadoes can whip all matter of objects—apples, corn, golf balls—high into the atmosphere, and the rain cycle can bring them crashing back down days later in a new place. It’s not all snacks and recreation: the gore of blood rain seems tame when it’s raining dead frogs, fish, or birds.
Anomalies aside, our biggest concern with liquid precipitation on earth is acid rain. Most rainwater has a slightly acidic pH, but gasses like sulfur dioxide and nitrogen oxide—primarily products of pollution—react with water molecules and introduce more acidity. Over time, acid rain harms soil, lakes, insects, and even buildings.
Acid rain on earth has a pH below 5.7, and can fall below 2 in highly industrialized areas and near volcanoes. Meanwhile, on Venus, the atmospheric acid rain barely reaches a pH of 1. It would be incredibly corrosive if the planet weren’t such a death trap in the first place: temperatures on Venus are so hot that sulphur dioxide evaporates before rain ever reaches its surface.
That’s right: weird rain is going interplanetary. Based on observations and atmospheric data, there’s a case to be made for a kind of “diamond rain” on our solar system’s gas giants (Jupiter, Saturn, Uranus, and Neptune). Carbon or methane in the upper atmospheres of these planets is compressed, and as it descends deeper into the planet, that pressure builds to eventually form plummeting diamonds.
If we look beyond our pocket of sky, we find more worlds of weird in the rain category. On HD 189733b, a gas giant that orbits very close to its star sixty-three light-years away from us, temperatures are so high that it rains molten glass. Much further into the galaxy, at 1,400 light-years from earth, WASP-178 b is bigger than Jupiter and whipping around a star almost twice as hot as our Sun at an extremely close distance. And on its night side, it’s raining molten rock. That dead fish rain isn’t sounding so bad.
The rain I’m most excited about right now is much closer and more hopeful—and unable to ruin a day at the beach. I’m entranced by recent research into rain on the moon. To put it in criminally simple terms, hydrogen and oxygen ions are constantly escaping earth. For five days each month, the moon is positioned to affect the movement of those ions. Many fall back to earth, but some are intercepted by the moon instead. On the cold surface of the moon, those ions form a permafrost—which may one day be part of a water source for lunar colonies.
I have conflicting thoughts about moon colonies. The science of it intrigues me almost as much as the resource-hungry capitalistic predation of it repulses me. Yet this whisper of rain seems almost like a welcome: we’re in this together, the earth and the moon. From here we’ll look for all the rain in the galaxy.