The Earth is a rocky planet with a vast ocean. About 70% of its surface is ocean. It is not difficult to imagine that if there were more water on the Earth, the entire Earth's surface would be covered by the ocean.
In fact, if this is the case, then the earth will become a " ocean planet ". Interestingly, astronomers may have discovered such strange planets, and they have discovered two at once.
On December 15, 2022, a team of astronomers from the University of Montreal published a paper in "Nature Astronomy" stating that they discovered two ocean planets around a star named "Kepler-138".
The team’s research shows that the volumes and masses of the two planets are very similar, and more than 50% of the materials that make them up are water. In addition, they also have atmospheres, which can provide the water on the planet’s surface with pressure to maintain a liquid state, which means that life may exist there.
"Kepler-138" is a red dwarf star . It is located in " Lyra " in the sky and is about 218 light years away from us. Observation data shows that this star has three planets, which in order from inside to outside are: "Kepler-138b", "Kepler-138c" and "Kepler-138d".
Among them, "Kepler-138b" is a common rocky planet, its size is almost the same as Mars , so it is inconspicuous, but the other two planets are different.
Observation data shows that the radii of "Kepler-138c" and "Kepler-138d" are both about 1.51 times that of the Earth, and their masses are 2.3 times and 2.1 times that of the Earth respectively. Based on this, it can be calculated that the average density of these two planets is about 3.6 grams/cubic centimeter.
Researchers believe that the densities of these two planets are very rare, because if their constituent materials are similar to those of the Earth, then in terms of their mass, their own gravity will "compress" them to be denser than the Earth, and their density should be higher than that of the Earth. However, the actual situation is that their density is much lower than the average density of the Earth (5.5 g/cubic centimeter), which shows that they are mainly composed of lighter materials.
In fact, this density is very close to Europa, a natural satellite of Jupiter in our solar system (the average density of Europa is about 3 grams/cubic centimeter). I believe everyone has a certain understanding of Europa. In short, Europa is a planet rich in water. Although its radius is only 1/4 of the earth, it contains more water than the earth.
Therefore, researchers initially speculated that "Kepler-138c" and "Kepler-138d" can be regarded as "enlarged versions of Europa." After that, researchers conducted computer simulations for these two planets. The simulation results showed that more than 50% of their compositions are water.
It is worth noting that although "Kepler-138c" and "Kepler-138d" are much closer to their host stars than the distance between the sun and the Earth, because their host star is a dim red dwarf, these two planets are located in the "habitable zone" of their host stars. That is to say, their planet surfaces are neither too cold nor too hot, just enough to meet the conditions for liquid water.
What will happen if two planets with such a huge water content happen to be located in the "habitable zone" of their host stars? Yes, the surface of their planet is likely to be completely covered by an ocean composed of liquid water, and such a planet is actually an ocean planet.
In fact, this is also the conclusion reached by the team. According to the planet model given by the team, "Kepler-138c" and "Kepler-138d" are both ocean planets. They both have a dense enough atmosphere, but they are not similar to the Earth. The same thing is that the gas in their atmosphere is mainly water vapor, and on the surface of their planet, there is an ultra-deep ocean covering the entire world, with an average depth of at least 2,000 kilometers. Relatively speaking, the average depth of the Earth's oceans is only about 3.7 kilometers.
(↑The left side is the cross section of the Earth, and the right side is the cross section of "Kepler-138c" and "Kepler-138d". Because the two ocean planets are very similar, only one model is needed)
Imagine that there are two planets larger than the Earth running around the same star, and both planets have such large oceans. Could life have been born there? Obviously, we cannot rule out this possibility. Unfortunately, we will not be able to verify this conjecture for a long time in the future. After all, these two ocean planets are too far away from us.
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