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The size of the raindrops helps determine the planets that may exist outside the solar system



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raindrop

Raindrops will also cause exoplanets to fall

One day, humans may set foot on another habitable planet. That planet may look very different from the Earth, but one thing will make people feel familiar-rain.

In a recently published paper JGR planetResearchers at Harvard University have found that in different planetary environments, raindrops are very similar, even if the planet and the earth are Jupiter. Understanding the behavior of raindrops on other planets is not only the key to revealing the ancient climate of similar planets, Mars But to identify potentially habitable planets outside our solar system.

The lead author of the paper, Kaitlyn Loftus, a graduate student in the Department of Earth and Planetary Sciences, said: “When we consider the habitability of planets, the life cycle of clouds is very important.”

; “But clouds and precipitation.” It’s really complicated, too complicated to be fully modeled. We are looking for a simpler way to understand how clouds evolve. The first step is whether cloud drops evaporate in the atmosphere or enter the ground on rainy days.”

Robin Wordsworth, Associate Professor in the Department of Environmental Science and Engineering at Harvard’s John Paulson School of Engineering and Applied Sciences (SEAS), and senior author of the paper, said: “The humble raindrops are important for all planetary precipitation cycles. component.” . “If we understand the behavior of individual raindrops, we can better represent rainfall in complex climate models.”

At least for climate modelers, an important aspect of raindrop behavior is whether raindrops will reach the surface of the earth, because atmospheric water plays an important role in planetary climate. For this reason, size is important.Too large, and due to insufficient surface tension, the droplets will break, whether it is water, methane or superheated liquid iron, such as Exoplanet Called WASP-76b. Too small, the water droplets will evaporate before hitting the surface.

Loftus and Wordsworth used only three attributes (droplet shape, falling speed, and evaporation speed) to determine the Goldilocks zone of raindrop size.

“The insights we gained by thinking about raindrops and clouds in different environments are critical to understanding the habitability of exoplanets.”
Robin Wordsworth, Associate Professor, Department of Environmental Science and Engineering

The shape of the water droplet is the same on different rainwater materials and mainly depends on the weight of the water droplet. Although many of us might think of traditional teardrops, raindrops are actually spherical when they are small, and gradually squeeze as the raindrops grow, until it becomes the top of a hamburger. The speed of descent depends on this shape and the thickness of gravity and surrounding air.

The evaporation rate is more complicated and is affected by atmospheric composition, pressure, temperature, relative humidity and so on.

Taking all these characteristics into account, Loftus and Wordsworth found that under a wide range of planetary conditions, the mathematical calculation of raindrops means that only a small fraction of the possible droplet size in the cloud can reach the surface.

Loftus said: “When we simulate cloud cycles on exoplanets, we can use this behavior to guide us.”

Wordsworth said: “The insights we have gained by thinking about raindrops and clouds in various environments are critical to understanding the habitability of exoplanets.” “In the long run, they can also help us understand the Earth itself more deeply. Climate.”

Reference: Kaitlyn Loftus and Robin D. Wordsworth, “The Physics of Raindrops in Different Planetary Atmospheres”, March 15, 2021, JGR planet.
DOI: 10.1029 / 2020JE006653

This research was funded by AST-1847120 from the National Science Foundation.




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