A new kind of exoplanet – half rock and half water – has been discovered around the universe’s most common stars, which could have big implications for the search for life in the cosmos. according to the researchers.
red dwarfs are the most common type of star, accounting for over 70% of the stellar population in the universe. These stars are small and cool, usually about one-fifth of their mass the sun and up to 50 times lower.
The fact that red dwarfs are so common has scientists wondering if they might be the best chance of discovering planets capable of possessing life as we know it on Earth. For example, in 2020, astronomers who discovered Gliese 887, the brightest red dwarf in our sky at visible wavelengths of light, can host a planet in its habitable zonewhere surface temperatures are adapted to accommodate liquid water.
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However, it is unclear whether the worlds orbiting red dwarfs are potentially habitable, in part due to researchers’ lack of understanding of the composition of these worlds. Previous research has suggested that small exoplanets – those less than four times the diameter of the Earth – orbiting sun-like stars are generally rocky or gaseous, possessing a thin or thick atmosphere of hydrogen and helium.
In the new study, astrophysicists sought to examine the compositions of exoplanets around red dwarfs. They focused on small worlds found closer – and therefore brighter and easier to inspect – to the red dwarfs observed by NASA. Transiting exoplanet study satellite (TESS).
Stars are much brighter than their planets, so astronomers cannot see most exoplanets directly. Instead, scientists generally detect exoplanets via the effects these worlds have on their starslike the shadow created when a planet passes in front of its star, or the small gravitational tug on the motion of a star caused by an orbiting planet.
By capturing the shadow created when a planet passes in front of its star, scientists can find the diameter of the planet. By measuring the small gravitational pull a planet exerts on a star, researchers can find its mass.
In the new study, astrophysicists ultimately analyzed 34 exoplanets for which they had precise diameter and mass data. These details helped researchers estimate the densities of these worlds and deduce their probable compositions.
“We can divide these worlds into three families,” study co-author Rafael Luque, an astrophysicist at the University of Chicago, told Space.com in an interview. In addition to 21 rocky planets and seven gaseous planets, they found six examples of a new type of exoplanet, watery, made up of about half rock and half water, either in liquid form or in the form of ice.
“It was a surprise to see evidence of so many water worlds orbiting the most common type of star in the galaxy,” Luque said. said in a press release (opens in a new tab). “This has huge implications for the search for habitable planets.”
The scientists’ planetary formation models suggest that the small planets they detected likely evolved in three different ways. Rocky planets may have formed from relatively dry material near their stars.
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Small, rocky planets have a density “almost identical to that of Earth,” study co-author Enric Pallé, an astrophysicist at the Canary Islands Institute of Astrophysics, told Space.com. “That means their compositions have to be very, very similar.”
In contrast, the watery planets are likely to have arisen from icy material and were born far from their stars, beyond the “ice line” where surface temperatures freeze. They then migrated closer to where astronomers detected them.
The gaseous planets are also rich in water and may have formed in the same way as the watery planets. However, they probably initially possessed more mass and therefore could gather an atmosphere of hydrogen and helium around them before venturing inwards.
Although rocky planets are relatively water-poor and watery planets are water-rich, that may not mean the former are arid and the latter are covered in oceans, the researchers said.
“Earth has only 0.02% of its mass as water, which makes it, from the point of view of astrophysics, a dry world, even if three quarters of the surface is covered with water”, Palle said. In contrast, although the watery planets the researchers found are half-filled with water, “that doesn’t necessarily mean they have massive oceans on their surface,” Pallé said, “the water seems mixed with the rock”.
Future research can see if these three types of worlds are also found around larger stars, Luque said. “A new generation of instruments in ground-based telescopes, especially in the United States and Europe, are going to allow us to make these measurements,” Luque said in the interview.
Another direction to follow is to study the composition and properties of these aquatic worlds. “With the James Webb Space Telescopewe can analyze their atmospheres, if they have any, and see how they store water,” Luque said in the interview. “That will tell us a lot about their formation, evolution, and internal structure.”
Scientists have detailed their findings (opens in a new tab) online Thursday (September 8) in the journal Science.
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New class of exoplanets! Half-rock, half-water worlds could be homes for life