a closeup of water drop

a closeup of water drop

Raindrops act similarly across the Milky Way, according to a new study. This should remain true whether we’re talking about a methane flood on Saturn’s moon Titan or an iron drizzle on the exoplanet WASP 78b. 

Raindrops Keep Fallin’

“You can make raindrops out of just about anything,” explains Kaitlyn Loftus. She studies planetary science at Harvard University in Cambridge, Massachusetts. She and her Harvard colleague Robin Wordsworth recently released new equations that describe what happens to a raindrop when it departs a cloud. 

Previous research has focused on rain in certain situations. Perhaps it was the Earth’s water cycle. It might also have been methane showers on Saturn’s moon Titan. This is the first study to explore rain composed of any liquid. 

According to astronomer Tristan Guillot, the authors “propose something that may be applied to every planet.” “That’s very cool,” he continues. He works at the Côte d’Azur Observatory. It is located in Nice, France. 

Clouds have the ability to heat or cool the surface of a planet. Rains aid in the movement of chemical components and energy throughout the atmosphere. Scientists seek to learn about other planets’ atmospheres, particularly their clouds and temperature. Understanding rain size, according to Guillot, is “really needed” for this. 

Clouds vs. Rain

Clouds are complicated. Even on Earth, scientists don’t fully understand how they develop and evolve. Raindrops, on the other hand, are regulated by a few simple physical principles. Drops of any liquid have the same spherical form when they fall. The pace at which a droplet evaporates is proportional to its surface area. 

“This is essentially fluid mechanics and thermodynamics,” adds Loftus. And those, she claims, “we very well comprehend.” 

She and Wordsworth discussed many types of rain. This includes water droplets on early Earth, current Mars, and K2 18b, a gaseous exoplanet. That last planet might have clouds of water vapor. The team also studied Titan’s methane rain, Jupiter’s ammonia “mush balls,” and iron rain on WASP 76b, an ultrahot gas giant exoplanet. “All of these various [rains] behave in the same way,” she discovers. This is because they must all adhere to the same physical rules. 

The pair discovered that worlds with higher gravity create smaller raindrops. Nonetheless, all of the raindrops they examined fell within a limited range. Their radius was barely a few millimeters to a tenth of a millimeter (a few thousandths of an inch). Loftus and Wordsworth discovered that larger droplets split apart as they descend. More minor drips, on the other hand, may evaporate before they touch the ground (for planets that have a solid surface, anyway). This would maintain the moisture in the air. 

Eventually, the researchers hope to expand their research to include solid precipitation such as snowflakes and hail. But it will not be simple. That is considerably more difficult to calculate. Loftus believes that the proverb “every snowflake is unique” is correct. 

According to Björn Benneke in Canada, this new study is the first step toward understanding precipitation in general. He is the astronomer from the University of Montreal who found water vapor in the atmosphere of K2 18b. Understanding extraterrestrial atmospheres is “what we’re all searching for,” he says. Astronomers want to acquire a reasonably general understanding of how atmospheres and planets operate. He believes it is critical to “not only be entirely Earth-centric.”