Discovery of two oceanic planets | Pres

“This is a great discovery in outer space astronomy,” explains astrophysicist Bjorn Benneke of the University of Montreal, one of the authors of the study published in the journal Jupiter. Natural Astronomy. “This is the first time we have two exoplanets, and the only good explanation for their low density is water or a good portion of their mass in low-density material.”

Kepler-138c and Kepler-138d, located in the Lyra constellation 218 light-years from Earth, are slightly larger than Earth. Thanks for the pictures from the space telescope Hubble And Spitzer, Montreal researchers found that their density suggests these exoplanets are made of material lighter than rock, but heavier than the hydrogen or helium that make up the bulk of gas giants like Jupiter. “We’re talking about nitrogen, methane and water,” says Benneke. Water should dominate. An ocean composed mostly of water should occupy a quarter to a half of the exoplanet’s volume.

In August, the same team discovered another “ocean” exoplanet, TOI-1452 b. “But it’s a more likely candidate than any other ocean exoplanet identified so far,” Benneke said. With Kepler-138 c and d, we are almost certain. »

Great pressures

A 2000 km deep ocean means immense pressures that can turn a mixture of water, methane and nitrogen into a “supercritical” fluid that has the properties of both liquids and solids.

Two exoplanets are described Natural Astronomy It has three times the diameter of Earth, but twice the mass. “Most Earth-like exoplanets are rocky. Kepler-138c and d are close to Saturn and Jupiter’s icy moons Enceladus and Europa. »