Two more 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 coldest 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 are “unlike any planet in our solar system”.
The upshot is that the planets are most likely made of water, according to a study published in Nature Astronomy on Thursday. A research team led by Caroline Piaulet, a doctoral 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 knew there were three exoplanets — the term for planets outside our solar system — within the Kepler-138 system, but they’ve just discovered that only two of them likely consist of water.
They also discover evidence of a previously undescribed fourth planet.
But the result is not as simple as it seems. Scientists have not detected water directly on the outer planets Kepler-138c or Kepler-138d. Instead, they compared the sizes and masses of the planets to comparison models.
When they compared the planets to the models, they found “that much of their volume—or even half—must be made 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 a large part of their total volume is probably composed of water.”
“This is the best evidence yet for water worlds, a type of planet that astronomers have long assumed exists,” Beneke continued.
The high temperatures on these planets indicate that they could be surrounded by a vapor 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 thick, dense atmosphere made of steam on this planet,” Paulet said in the letter. “Only, under this vaporous atmosphere, can there be liquid water under high pressure, or even water in another phase that occurs at high pressure, which is called a supercritical liquid.”
Waterworlds lie outside the habitable zone of their stars – the area where temperatures allow liquid water to exist on a rocky planet’s surface, which could support life. The new planet described by the researchers, Kepler-138-e, is located in exactly that right region, the statement said.