Watery exoplanets are often dry, study finds

Watery exoplanets are often dry, study finds

Semi-aquatic planets often look like Arrakis from the book and film saga Dune.

  • Research on small red dwarf planets has determined how abundant water worlds are.
  • Exoplanets that contain about half water have been found to be much more abundant.
  • Despite this, their surface is mostly dry – they have not only liquid, but also frozen water.
  • Rather, it is part of the bowels of their planets, which fundamentally changes the view of the origin of these bodies.

The presence of water is considered the basic condition for the creation and maintenance of life. Well, it must be liquid water.

However, a new study investigating just how abundant water-rich exoplanets are has come to a surprising conclusion. Even water-rich cosmic bodies outwardly resemble arid desert worlds. Research work Published The scientific journal Nature.

Rock, water, gas

Astronomers find exoplanets in a variety of ways. Most often, by measuring the dip in light that occurs when examining a planet orbiting a star. Or on the basis of the small but measurable motions of the star, it revolves around the worlds.

While the first method can reveal the dimensions of a distant planet, we use the second to reveal its mass.

If we know both parameters – diameter and weight, we can calculate the structure. In other words, we distinguish gaseous worlds such as Jupiter, which are relatively “light”, from rocky worlds, which, on the contrary, are relatively “heavy” for their size.

A very high weight reveals the metal world. “Transitional,” that is, one that falls between the values ​​we expect from the gaseous or stony world, because a transition reveals the water world.

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Rapid expansion of knowledge

A team of Spanish researchers decided to take a closer look at planets whose dimensions and masses are known. Calculate their composition.

Scientists were particularly interested in water worlds around red dwarfs – small and very bright stars. Eight out of ten stars in the Milky Way belong to this category.

Until now, research has analyzed the composition of planets individually. However, the Spanish researchers decided to expand the existing knowledge by leaps and bounds. They determined the composition of the 43 worlds.

A surprisingly high percentage of planets with large size-to-mass ratios indicate a watery world. According to calculations, water makes up about half of their weight.

“It’s surprising to see evidence for so many water worlds around the most common type of star in our galaxy,” says lead author Raphael Luk, currently at the University of Chicago. “This fact has huge implications for the search for habitable planets,” he adds.

A traditional view of the form of water worlds.

Source: Anyone

Dry water worlds?

At the same time, the studied worlds orbit too close to their parent stars to retain liquid water on their surfaces. In short, they are very hot – more like Mercury than Earth.

They hold water only in the form of a very fine gas. Therefore, large amounts of surface water indicate the presence of a vast warm atmosphere.

However, this scenario is inconsistent with observations. They rule out the presence of an extensive gaseous atmosphere for the investigated water world.

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Instead, analysis of the data suggests that water is part of their gut. Basically, it forms a mixture of crust and mantle.

“I was shocked when I saw the results of this analysis. Like many other planetologists, I assumed that these outwardly dry bodies were just rocks. But they are all water worlds,” says Jacob Bean, a member of the wider research team.


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They came differently

The discovery that many planets orbiting close to stars are half water confirms an old hypothesis of planetary evolution.

Cosmic bodies rich in water cannot form near their parent stars – their glow from the disk, from which the planets that form suck the mass, and all the ice evaporates.

At first, water-rich worlds orbiting the hottest corners of the planetary system were thought to have formed at icy distances and then migrated inward.

Prior to this theory, in recent years, the idea that water-rich comets and asteroids collided with water to planets orbiting near stars was preferred. This scenario can explain the amount of water at a few percent levels by mass, as we see in the case of Earth. But not water, which makes up 50% of the weight and is mostly contained in underground rocks.

Therefore, many water-rich exoplanets appear to be actually water-rich because they were born in a very different place than the one they orbit today. In the cold and dark regions of the planetary system.

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