Two distant planets are likely made of water, according to research using NASA’s Hubble and Spitzer telescopes.
The so-called “water worlds” orbit a red dwarf star, which is the smallest and coolest type of star, according to a press release from NASA’s Jet Propulsion Laboratory.
NASA says the water planets are 218 light-years away in the constellation Lyra. The agency said they “do not resemble any planets in our solar system.”
The finding that the planets are likely to be composed of mostly water comes from a study published in the journal Nature Astronomy on Thursday. A research team led by Caroline Piaulet, a PhD student at the University of Montreal’s Institute for Exoplanet Research, used NASA’s Hubble and Spitzer space telescopes to observe the distant planetary system.
The planetary system they studied is called Kepler-138 because it is in the field of view of NASA’s Kepler spacecraft. Researchers have known about the existence of three exoplanets — the term for planets outside our solar system — within the Kepler-138 system, but have just discovered that only two of them are likely to be made of water.
They also discover evidence of a fourth planet that has not been described before.
But the result is not as straightforward as it might seem. Scientists have not directly detected water on the outer planets Kepler-138c or Kepler-138d. Instead, they compared the sizes and masses of the planets to models for comparison.
When they compared the planets to the models, they found “that a good part of their volume—even half of it—must be made up of materials lighter than rock but heavier than hydrogen or helium.”
NASA says water is the most likely candidate for a substance that is lighter than rock but heavier than hydrogen or helium.
Bjorn Bencke, co-author of the study and professor of astrophysics at the University of Montreal, said in the release. “However, we have now shown that these two planets, Kepler-138c and d, are very different in nature and that much of their entire volume is likely composed of water.”
“It’s the best evidence yet for water worlds, a type of planet that astronomers have long assumed existed,” Beneke continued.
The high temperatures on these planets indicate that they may be surrounded by a vaporous atmosphere, according to NASA.
“It is likely that the temperature in Kepler-138d’s atmosphere is above the boiling point of water, and we would expect a dense, dense atmosphere made of steam on this planet,” Piaolet said in the statement. “Only, under this vaporous atmosphere, can there be liquid water under high pressure, or even water in another phase occurring at high pressures, called a supercritical liquid.”
The “water worlds” lie outside their star’s habitable zone — the region in which temperatures allow liquid water to exist on a rocky planet’s surface, potentially supporting life. But the new planet described by the researchers, Kepler 138-e, is in just that right region, according to the release.
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