A Strangely Comforting Finding About Alien Rain
On rainy days, Kaitlyn Loftus likes to imagine herself somewhere else. Not on a sun-soaked beach, but on another world in the middle of its own rainstorm. Beneath the swirling storms of Jupiter or Saturn’s hazy cloud tops, where helium drops from the sky. On Neptune, where it might drizzle diamonds. Maybe Titan, a moon of Saturn, where methane rain can fill entire lakes.
Loftus is a planetary scientist at Harvard, and for her, otherworldly rain is more than a daydream. She and her colleagues recently studied how liquid droplets might behave as they descend from the clouds of different worlds, on the planets and moons in our solar system and distant planets around other stars. The team had expected to find quite a bit of variation; the conditions on Earth, after all, bear little resemblance to the environments of the other celestial bodies we know. Of the exoplanets that astronomers have discovered so far, some of them have weird characteristics—rocky surfaces so stretchy they resemble toffee, puffy atmospheres that might as well be planetary cotton candy, toasty worlds hotter than most stars.
Instead, their research suggests that raindrops on other worlds may not be so different from those on our own. Liquid droplets, whether they’re made of water or something more unusual, fall to the ground as spherical blobs that are roughly the same size. The biggest methane raindrops on Titan, for example, would only be about twice the size of the biggest water raindrops on Earth. In one sense, the similarities across worlds are not so surprising. The universe is full of echoes, from the basic composition of atoms and molecules to the fundamental forces that shape planets and galaxies. But there is something especially intriguing, even comforting, about finding uniformity in a phenomenon that seems so distinctly Earthlike, so specific to our existence as beings on this planet.
