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Scientists work out what rain is like on other planets (and it could help us find habitable worlds)

Dust storm of the surface of Titan, illustration. Titan, the largest moon of Saturn, is the only body in the known Solar System, aside from Earth, with liquid on its surface. But it's not water; it's liquid hydrocarbons. It's also the only satellite with a substantial atmosphere, made mostly of nitrogen. Scientists studying data from the Cassini mission by ESA have found dust storms raging around the moon's equator, as depicted in this illustration. Saturn is shown in the sky, although in reality it is unlikely it would be visible owing to the dense cloud coverage.
On Saturn’s moon Titan, it rains methane, or liquified natural gas – and on Neptune, scientists suspect it rains pure carbon in the form of diamonds. (Getty)

If you’ve ever wondered what rain might feel like on Jupiter, or on Saturn’s icy moon Titan, wonder no longer.

Researchers have found that raindrops are remarkably similar across different planets, even planets as drastically different as Earth and Jupiter.

The paper, by AGU and Harvard researchers, could help scientists unravel the ancient climate on planets like Mars – and find potentially habitable planets outside the solar system.

Raindrops on Earth are made of water – but on Venus it rains sulphuric acid; on Jupiter, it rains helium and mushy ammonia hailstones.

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On Mars, it snows carbon dioxide, or dry ice.

On Saturn’s moon Titan, it rains methane, or liquified natural gas – and on Neptune, scientists suspect it rains pure carbon in the form of diamonds.

Raindrop sizes on different planets (AGU)
Raindrop sizes on different planets. (AGU)

The results also show the maximum size of liquid droplets that fall as rain is similar across varying planetary conditions.

Different types of liquid droplets would max out around half to six times the size of water rain on Earth, depending on the strength of the planet’s gravitational pull (the stronger the gravitational pull, the smaller the raindrop).

Kaitlyn Loftus, a planetary scientist at Harvard University, said: “There’s a fairly small range of stable sizes that these different composition raindrops can have; they’re all fundamentally limited to be around the same maximum size.

"The lifecycle of clouds is really important when we think about planet habitability.

“But clouds and precipitation are really complicated and too complex to model completely.

“We're looking for simpler ways to understand how clouds evolve, and a first step is whether cloud droplets evaporate in the atmosphere or make it to the surface as rain.

"We can use this behaviour to guide us as we model cloud cycles on exoplanets.”

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Robin Wordsworth, associate professor of environmental science and engineering at the Harvard John A Paulson School of Engineering and Applied Sciences, said: "The humble raindrop is a vital component of the precipitation cycle for all planets.

"If we understand how individual raindrops behave, we can better represent rainfall in complex climate models.

“The insights we gain from thinking about raindrops and clouds in diverse environments are key to understanding exoplanet habitability.

"In the long term, they can also help us gain a deeper understanding of the climate of Earth itself."

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