IMAGE: An infographic comparing the projected size of raindrops on different planets. Note that Titan and present-day Mars are too cold for raindrops of liquid water. view month
Credit: Image credit: AGU
WASHINGTON – Raindrops on other planets and moons are close to the size of raindrops on Earth despite having different chemical compositions and falling through very different atmospheres, according to a new study. The results suggest that raindrops falling from clouds are surprisingly similar in a wide range of planetary conditions, which could help scientists better understand the climates and precipitation cycles of other worlds, according to the researchers.
Raindrops on Earth are made of water, but other worlds in our solar system have precipitation made for more unusual things. On Venus, it rains sulfuric acid; on Jupiter, it rains hail of helium and ammonia. On Mars it snows carbon dioxide or dry ice. On Saturn’s moon, Titan, it rains methane or liquefied natural gas. And in Neptune, scientists suspect that it rains pure carbon in the form of diamonds. It could even rain iron or quartz on some planets if conditions were right.
A new study examining the physics of how liquid droplets behave as they fall from clouds finds only droplets in clouds within a limited size range (between about one-tenth of a millimeter and several millimeters in radius) can reach on the surface of rocky planets as rain. This is a fairly narrow range of sizes, as raindrops increase in volume about a million times during their formation within a cloud.
The results also show the maximum size of liquid droplets falling as rain is similar in different planetary conditions. The different types of liquid droplets would reach half of up to six times the size of the rain of water on Earth, depending on the force of the planet’s gravitational attraction (the stronger the gravitational attraction, the more small will be the raindrop). Here you will find an infographic comparing the size of raindrops on Earth, Mars, Jupiter, Saturn and Titan.
“There’s a fairly small range of stable sizes that can have these different raindrops of composition; they’re all basically limited to about the same maximum size,” said Kaitlyn Loftus, a planetary scientist at Harvard University and lead author of the new study at AGU’s Journal of Geophysical Research: Planets, which publishes research on the formation and evolution of planets, moons, and objects in our solar system and beyond.
It rains on other worlds
In the new study, Loftus and his partner Robin Wordsworth used the principles of mathematics and physics to model how drops of liquid water fall through planetary atmospheres. They wanted to determine the possible size ranges for drops falling from a cloud to a planetary surface. Too large raindrops split into smaller ones, while too small raindrops evaporate before they touch the ground.
They first determined the possible size ranges for raindrops on rocky planets such as Earth and Mars, given atmospheric conditions such as temperature, air pressure, relative humidity, distance from the cloud to earth and the force of the planet’s gravitational pull.
They found that raindrops with a radius of less than a tenth of a millimeter evaporate before reaching the surface and raindrops of more than several millimeters in radius break into smaller droplets as they that fall.
Then they watched as raindrops would fall on much larger planets, such as Jupiter and Saturn, which have very different atmospheres. Comparing the modern Earth, the ancient Mars, and these larger planets, they found that raindrops move water through the air in a similar way, although what constitutes “air” varies greatly between the planets.
Even when different liquids form raindrops, these alien raindrops are not as different from family water raindrops, according to the researchers ’calculations. For example, Titan’s largest methane raindrops would be about twice the size of water rain on Earth. Loftus does not know clearly why the maximum size of raindrops is so uniform, but he suspects that it may be due to how the surface tension of a droplet relates to its density.
The findings will help scientists better simulate conditions on other planets, as precipitation is a key component in the planet’s climate and nutrient cycles, Loftus said. Modeling the appearance of precipitation in a distant world could also help researchers interpret observations of exoplanetary atmospheres made by space telescopes, said Tristan Guillot, a planetary scientist at the Observatory of the Côte d’Azur in Nice, France. was not connected to the new studio.
“Now with instruments like [the James Webb Space Telescope], which we hope will be launched soon, we will have the ability to detect very good spectra of exoplanetary atmospheres, including those that are much cooler than we can normally characterize, in which clouds and rain will occur, “Guillot said.” therefore, such tools as they are developed will be very useful and important in interpreting these spectra. ”
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Paper title: “The physics of falling raindrops in various planetary atmospheres”
Authors:
- Kaitlyn Loftus, Harvard University, Cambridge, Massachusetts
- Robin D. Wordsworth, Harvard University, Cambridge, Massachusetts
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