Precipitation is much more widespread in this solar system than is generally believed. Obviously it is raining water on earth. But carbon dioxide is snowing on Mars, methane is raining on titanium, sulfuric acid is raining on Venus, and it could possibly rain diamonds on Neptune. The nature of the material falling from the sky is almost as varied as the planets themselves. New research by a team led by Kaitlyn Loftus at Harvard has shown similarity for all liquid materials that make rain throughout the solar system – all drops, regardless of material, are approximate same size.
There are two main reasons for this: small raindrops evaporate, while large raindrops separate into smaller ones. To determine how high these values could be, the scientists examined how large droplets could be on Earth-like planets such as Mars or Venus.
Planets outside of our solar system could also have rain.
As expected, the result of these models showed drops with a radius of less than 1/10 millimeter that had evaporated before hitting the ground. Larger drops with a radius of more than a few millimeters, on the other hand, would split up into drops that are closer to the average size.
Even with larger planets, there was no dramatic difference in size. Rain on Jupiter or Saturn would be similar in size and shape to rain on Earth or Mars. Similarly, the material that raindrops are made of did not have a particularly large impact on the drop size. For example, it rains methane on titanium. The study found that the largest of these methane droplets is only about twice the size of the average droplet on Earth, despite Titan’s dramatically different gravity and weather patterns.
Graphic showing the rainy cycle on Jupiter involving ammonia hailstones.
Photo credit: NASA / JPL-Caltech / SwRI / CNRS
It’s not yet clear why exactly this uniformity exists, although the team believes it has to do with the density and surface tension of the material. Understanding this relationship is not the only beneficial outcome of further study in this area. Understanding how raindrops form on other planets could help exoplanetologists understand the atmosphere of exoplanets, which will become a much more cautious topic with the launch of much more powerful exoplanet observation satellites in the near future.
While it can take a long time for someone to personally experience rain on another world, it is a comforting thought to know that they are not too different from their own rain on earth. And when a person actually witnesses it first hand, it becomes even more amazing.
Learn more:
AGU – Alien raindrops surprising like rain on earth
AGU – The physics of falling raindrops in different planetary atmospheres
Astronomy.com – Raindrops on other worlds are surprising like our own
Physics World – Sweet taste of heavy water, raindrops falling on other planets
Mission statement:
Infographic with the different sizes of raindrops on different worlds.
Photo credit: AGU
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