Surprising discovery suggests 'water worlds' are more common than we thought

Surprising discovery suggests ‘water worlds’ are more common than we thought

Asteroid demographics around M dwarfs. Credit: Rafael Luque (University of Chicago), Pilar Montañés (@pilar.monro), Gabriel Pérez (Instituto de Astrofísica de Canarias) and Chris Smith (NASA Goddard Space Flight Center)

Water is something that all life on Earth needs, and the cycle of rain to rivers to oceans to rain is an essential part of keeping Earth’s climate stable and pleasant. When scientists talk about where to look for signs of life across the galaxy, planets with water always top the list.


A new study published in science suggests that more planets may have more water than previously thought — as much as half water and half rock. capture? All of this water may be embedded in the rock, rather than flowing like an ocean or surface river.

“It was surprising to see evidence of so many water worlds orbiting the most common stars in the Milky Way,” said Rafael Luque, a postdoctoral researcher at the University of Chicago and lead author of the new paper. Habitable planets make a huge difference.”

Planetary Population Pattern

Thanks to better telescope instruments, scientists are finding more and more signs of planets in distant solar systems. Larger sample sizes help scientists identify population patterns—similar to how looking at the population of an entire town can reveal trends that are hard to see at the individual level.

Luque, along with co-author Enric Pallé of the Institute of Astrophysics of the Canary Islands and the University of La La Laguna, decided to conduct a population-level study of a group of planets orbiting a type of star known as M-. dwarf. These stars are some of the most common we see around the Milky Way, and scientists have catalogued dozens of planets around them so far.

Surprising discovery suggests 'water worlds' are more common than we thought

Artistic impression of the water world. Credit: Pilar Montañés (@pilar.monro)

But since stars are so much brighter than their planets, we can’t see the actual planets themselves. Instead, scientists found faint signs of the planet’s influence on its star — the shadows created when the planet passes in front of its star, or the tiny tug of motion of the star as the planet orbits. That means there are still many questions about what these planets actually look like.

“Two different ways of finding planets give you different information,” Paley said. By capturing the shadows a planet creates as it passes in front of its star, scientists can find a planet’s diameter. By measuring the tiny gravitational pull a planet exerts on a star, scientists can find its mass.

By combining these two measurements, scientists can understand the composition of the Earth. Maybe it’s a large, airy planet, composed mostly of gas like Jupiter, or a small, dense, rocky planet like Earth.

These analyses were performed on individual planets, but rarely on the full known population of such planets in the Milky Way. When the scientists looked at the numbers — 43 planets in all — they saw a surprising picture.

The densities of most planets suggest they are too light to be made of pure rock. Instead, the planets could be something that is half rock and half water, or another, lighter molecule. Imagine the difference between picking up a bowling ball and a soccer ball: they’re about the same size, but made of lighter materials.

Surprising discovery suggests 'water worlds' are more common than we thought

Artistic impression of water world landscape. Credit: Pilar Montañés (@pilar.monro)

Find the water world

It might be tempting to think of these planets as something out of Kevin Costner’s water world: completely covered by the deep ocean. However, these planets are so close to their sun that any water on the surface would exist in a supercritical gas phase, which would expand their radii. “But we didn’t see that in the samples,” Luke explained. “This suggests that the water is not in the form of a surface ocean.”

Instead, water may be mixed into rocks or pockets below the surface. These conditions are similar to Jupiter’s moon Europa, which is thought to have liquid water underground.

“I was shocked when I saw this analysis — I and many in the field thought these were dry, rocky planets,” said University of Chicago exoplanet scientist Jacob Bean, whose team Luque has joined to further analyze.

The finding fits with exoplanet formation theories that have fallen out of favor over the past few years, suggesting that many planets formed farther out in their solar system and migrated inward over time. Imagine rock and ice formed together in cold conditions far from a star, then slowly pulled inward by the star’s gravity.

While the evidence is compelling, Bean said he and other scientists would still like to see “hard evidence” that one of these planets is a water world. That’s what scientists hope to do with the JWST, NASA’s newly launched space telescope, the successor to Hubble.


There are as many as 6 billion Earth-like planets in our galaxy, according to new estimates


More information:
Rafael Luque, density, not radius, separates rocky and water-rich asteroids orbiting M dwarfs, science (2022). DOI: 10.1126/science.abl7164. www.science.org/doi/10.1126/science.abl7164

Johanna Teske, Three Planets Around Red Dwarfs, science (2022). DOI: 10.1126/science.add7175. www.science.org/doi/10.1126/science.add7175

Courtesy of the University of Chicago

Citation: Surprising discovery suggests ‘water worlds’ are more common than we thought (September 8, 2022), September 8, 2022 from https://phys.org/news/2022-09-worlds-common -thought.html retrieved

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