In a new study, scientists discovered that raindrops on Earth are similar to raindrops found on other planets and moons, which is surprising considering the differences between our raindrops versus ones from other planets.

Two Harvard University scientists, Kaitlyn Loftlus and Robin Wordsworth, conducted the study, using equations to examine how raindrops behave on other planets compared to our own on Earth.


What You Need To Know

  • Two scientists compared raindrops from Earth to other planets and found similarities 

  • Raindrops are shaped like hamburger buns

  • The size of a raindrop is related to the planet's gravitational pull

  • The study could help scientists understand climates and precipitation cycles on other planets

Regardless of how different a planet is from Earth or what its rain is made of, the raindrops’ maximum size does not differ very much from the raindrops we see on Earth.

Scientists hope to better understand the climates and precipitation cycles outside our own with the latest findings.

Raindrops 101

In elementary school, we learned the basics of a raindrop. Rain is made of water and raindrops fall from a cloud in the sky.

But there’s more!

Rain starts within a cloud, where you’ll find countless cloud droplets suspended in the air. Through a process called collision and coalescence, these droplets become larger and eventually grow enough to fall from the cloud as rain.

An "average" raindrop is roughly 2 millimeters wide but can be up to 5-11 millimeters in diameter.

From light drizzle to pouring rain, the size typically relates to the rainfall’s intensity.

Raindrops begin as spheres. Then, as the raindrops fall from a cloud, the bottom flattens because of the force of air pushing upward. The medium to larger raindrops take on the shape of a hamburger bun or a parachute!

Gravity and raindrop size

About 71% of the Earth’s surface is covered by water, so it's no wonder our raindrops are made up of water! However, water is much harder to come by, if not impossible to find, on other planets.

So, how does it rain on alien worlds?

In the new study, researchers discovered that precipitation is actually made of more unusual stuff. For example, according to the results, it rains sulfuric acid on Venus. On Jupiter, the rain is made of helium, while Mars has carbon dioxide snow.

Could you imagine a meteorologist forecasting a storm of dry ice on Mars?

Loftlus and Wordsworth's research explains how raindrops on other planets fall similarly to our rain. The raindrops’ maximum size does not differ much, either.

According to the study, the limiting factor for how large raindrops can grow is due to the gravitational pull from the planet or moons. So, the stronger the gravity is, the smaller the raindrops will be on various worlds in our solar system.

Image: AGU

What is interesting about the graphic above is that it would appear that the raindrops have a wide range of sizes, but that’s not the case. Within the research, we learn that when you consider the relative mass and gravitational pull of these worlds, the difference is not as wide as expected.

For example, gravity on Jupiter is more than two-and-a-half times greater than Earth’s gravity, meaning smaller drops. Meanwhile, the moon Titan’s gravitational pull is much weaker than Earth’s, so the maximum raindrop size is larger.

The shape is also key and they discovered the "hamburger bun" shape is optimal, even on other planets. Maybe it’s time to retire the "classic" raindrop? Hamburger bun raindrops, it is!

Furthermore, the results suggest that if a raindrop’s size is too small, it tends to evaporate quickly. If the raindrop is too large, it is more likely to split, and the two smaller drops can also evaporate quickly.

So, there’s a specific range of raindrop sizes that are most likely to survive from the cloud to the ground on any planet.

Comparing our raindrops to other alien worlds helps us understand a planet’s water cycle.

“The humble raindrop is a vital component of the precipitation cycle for all planets," says Wordsworth, who is an Associate Professor at Harvard School of Engineering and Applied Sciences. He adds, “if we understand how individual raindrops behave, we can better represent rainfall in complex climate models.”