Astronomers using the Hubble Space Telescope have long observed two exoplanets that may be examples of a hypothetical planetary classification: a aquatic world.
The planets are known as Kepler-138c and Kepler-138d and are located in a star system 218 light-years away, according to a announcement of the European Space Agency. The team, led by Caroline Piaulet of the Université de Montréal Institute for Exoplanet Research, used data from NASA’s Hubble and Spitzer Space Telescope to determine that the worlds are largely water, making them even wetter than our famous home planet. Their findings are publican en Nature Astronomy.
“We previously thought that planets that were slightly larger than Earth were big balls of metal and rock, like enlarged versions of Earth, and that’s why we call them super-Earths,” said Björn Benneke, one of the study’s authors. , in the ESA statement. “However, we have now shown that these two planets, Kepler-138c and d, are quite different in nature and that a large fraction of their total volume is likely to be made up of water.”
Kepler-138c and Kepler-138d are estimated to be about three times the size of Earth and twice the mass of our own planet, but with much lower densities.
The research team did not directly observe the water on the planets, but by comparing the observational data with pre-existing models, they found that it should consist of materials with a density between the gases hydrogen and helium and rock, with the likely candidate being water. That said, the researchers believe that these planets could have incredibly hot atmospheres, which means their surfaces might not be littered with vast liquid oceans.
“The temperature in Kepler-138d’s atmosphere is probably above the boiling point of water, and we expect a thick, dense atmosphere made of steam on this planet,” Piaulet said. “Only under that steamy atmosphere could there be high-pressure liquid water, or even water in another phase that occurs at high pressures, called supercritical fluid.”
Some of the first direct evidence for the existence of aquatic worlds they met in 2012, but subsequent observations have been hard to come by. A study conducted in 2017 suggested that these aquatic worlds could make up a large percentage of potentially habitable exoplanets. Other research in 2019 found that exoplanets larger than Earth, such as the Kepler-138 planets, could likely be water worlds with incredibly deep oceans.
While the recent findings are exciting, the research team hopes to continue work using the Webb Space Telescope to further study the atmospheres of Kepler-138c and d.