Two super-earths turn out to be water worlds - but there are no oceans
Created: 12/16/2022 13:36
By: Tanya Banner
Artist's rendering: Exoplanet Kepler-138d is visible in the foreground, with exoplanet Kepler-138c to the left.
In the background is the exoplanet Kepler-138b, also orbiting the red dwarf star Kepler-138.
According to current research, Kepler-138d and c are water worlds.
© NASA, ESA, and Leah Hustak (STScI)
On closer inspection, two exoplanets that have been known since 2014 are water worlds – a type of planet that astronomers have long suspected existed.
Montreal – It was discovered in 2014 that the red dwarf Kepler-138 is orbited by at least three planets.
Now, however, research has taken a closer look at two of these exoplanets - and found something unprecedented: the two planets, which are 218 light years away from Earth, are so-called water worlds.
A large part of the two planets consists of water - they are different from all planets in our solar system, as
reported
by fr.de.
In a study published in the journal
Nature Astronomy
, a research team led by Caroline Piaulet of the University of Montreal, Canada, describes the two exoplanets and the planetary system around the star Kepler-138 in more detail.
The researchers conclude from their sizes and masses that the two planets are water worlds.
The team theorizes that a significant portion of the planet's volume -- up to half -- is made up of materials lighter than rock but heavier than hydrogen or helium.
Exoplanets Kepler-138c and Kepler-138d are water worlds
The most likely candidate that meets these requirements is water.
"We first thought that planets slightly larger than Earth were big balls of metal and rock, like enlarged versions of Earth," explains astrophysicist Björn Benneke, co-author of the study, in a statement.
"That's why we called them super-Earths."
But the researchers were obviously wrong in the case of Kepler-138c and Kepler-138d.
"We have shown that these two planets are of very different nature and that a large part of their total volume is probably made up of water.
This is the best evidence so far for water worlds, a type of planet that astronomers have long suspected existed,” explains Benneke.
Astronomy has long suspected the existence of water worlds
The two exoplanets each have more than three times the volume of Earth, but much lower densities.
This surprised the researchers, because all the planets of this size that have been explored so far have been rocky planets like Earth.
The researchers compare the two newly identified water worlds to some icy moons in the solar system, which consist largely of water arranged around a rocky core: "Imagine larger versions of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn," explains Piaulet.
However, they would orbit their star closer and would be surrounded by envelopes of water vapor rather than having an icy surface like the two moons.
Even if the two exoplanets are largely made of water, the research team emphasizes that the two water worlds do not necessarily have to have oceans.
"The temperature in the atmosphere of Kepler-138d is probably above the boiling point of water and we expect a thick and dense atmosphere of water vapor on this planet," says Piaulet.
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More than 5000 exoplanets are now known - the number is constantly growing.
The James Webb Space Telescope is set to take a closer look at some exoplanets in the coming years.
Recently, it was able to show that it can study the atmosphere of an exoplanet.
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