Two Worlds Orbiting A Nearby Star Could Be More Than Half Water

There are two worlds around a tiny star 218 light-years away.

The names of the exoplanets are Kepler-138c and Kepler-137d. Both are around 1.5 times the radius of Earth, and both appear to be soggy worlds consisting of thick, steamy atmospheres and deep oceans.

"We used to think that planets that were a bit larger than Earth were balls of metal and rock, like scaled-up versions of Earth, and that's why we called them super-earths," says astronomer Bjrn Benneke of the University of Montreal.

We have shown that the two planets, Kepler-138c and d, are not the same as nature would have you believe. It's the first time we've seen planets that can be confidently identified as water worlds.

An analysis of another world found that it could be a water world, but more observations are needed. The work on the two planets is not as uncertain as the researchers think.

It takes a lot of detective work to figure out what planets are outside our Solar System. Direct images are very hard to get and don't show much detail because they are very far away.

The composition of an exoplanet is usually inferred from its density, which is calculated using two measures, one taken from the star's light by the planet and the other from the star's radial velocity.

The size of the exoplanet is determined by the amount of star light that is blocked by the transit. A regular but small expansion and contraction of the wavelength of the star's light is what causes radial velocity. How much mass an exoplanet has can be determined by the movement of this movement.

You can calculate the density of an object with its size and mass.

A world with a low density will beJupiter or Neptune. The world with the most metals will have higher densities. Earth is the densest planet in the Solar System with a t 5.5 grams per cubic centimeter.

The measured tugs on the two planets give us mass of 2.3 and 2.1 times that of Earth. The density of both worlds is somewhere between a rocky and a gaseous one.

The Jovian ice moon Europa has a density of 3.0 grams per cubic centimeter. The ocean is covered by an icy shell.

"Imagine larger versions of Europa or Enceladus, the water-rich moons circling Jupiter and Saturn, but brought much closer to their star", says astronomer and lead researcher of the research. The water-vapor envelopes would be different than the icy surface.

Water makes up more than 50 percent of the exoplanets' volume, according to the team's modelling. The average depth of the oceans is 3.8 kilometers.

The stars are very close to Earth. The two exoplanets are much hotter than our world because they are so close to that star. There are 13 and 23 day periods.

The researchers say that the oceans and atmospheres on these worlds are not likely to be as similar to our ocean.

"We expect a thick, dense atmosphere made of steam on these planets, because the temperature is likely above the boiling point of water."

There could be liquid water under that steam atmosphere, or even water in another phase that occurs at high pressures, called a supercritical fluid.

It's an alien, yes.

The research was published in a journal.