The stars surrounding Kepler-138 (Photo: NASA, ESA, and Leah Hustak (STScI))
A team of researchers from the University of Montreal in Canada found evidence that two exoplanets, orbiting a red dwarf star, are "water worlds", that is, celestial stars covering most of their surface.
The stars, found in the Kepler-138 system, are 218 light-years from us in the Lyra star cluster, and are different from any star in our solar system.
The team led by Carolyn Piolet, from the Trottier Institute for Distant Star Research, and published in "Nature Astronomy", reached its findings with the help of the two Spitzer space telescopes (which are no longer active) and the Hubble.
The stars, Kepler-138 c and d, along with another small star were already discovered by Hubble, but the team also found evidence of the existence of a fourth star in the system.
The discovery was not made through direct observation but through comparison with models, and reaching the conclusion that at least 50% of their surface is made of material lighter than rock, but heavier than hydrogen or helium (which is typical of gas giants, such as Jupiter), and the most likely material found in this area is... .water.
"We used to think that stars that were a little bigger than Earth were big balls of metal and rocks, that's why they were called "super-Earths", says Bjorn Benke, the research partner and professor of astrophysics in Montreal. "However, now we have shown that these two stars, Kepler-138 c ' and D', are different in nature and probably consist mainly of water.
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With three times the volume of Earth, and twice the mass of our star, these stars are less dense than Earth.
For the most part, stars of this size would be denser than Earth, and they are also covered in a rocky crust similar to our little globe.
However, one should not expect oceans: the temperature on the stars in Kepler is slightly above the boiling point of water, so it is likely that the surface of the star is covered with an atmosphere of water vapor or steam, and beneath it there may be water in a liquid state and at high pressure, or perhaps a completely different state of aggregation, adds research leader Piolet.
The researchers also as mentioned discovered evidence of a fourth star, named Kepler-138 e, in the area close to its brother.
It is a small planet and the farthest from its sun of the other three, with a 38-day pericycle.
The new star will require further research.
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