Using data from NASA’s Hubble and Spitzer Space Telescopes, astronomers have found evidence
that two exoplanets orbiting a star 218 light-years away are “water worlds,” where water makes
up a large fraction of the entire planet.
The planetary system, known as Kepler-138, have worlds that are unlike any planets in
our own solar system.
Astronomers didn’t directly detect water on the Kepler-138 planets.
Instead, they compared the planets’ sizes and masses to models that concluded up to
half of their volume should be made of materials lighter than rock but heavier than hydrogen
or helium.
The most common of these materials is water.
It is the best evidence astronomers have ever found for water worlds, a type of planet long
theorized.
Researchers caution that the planets may not have surface oceans like on Earth.
The temperature of one planet’s atmosphere is likely above the boiling point of water.
They expect a thick, dense atmosphere made of steam on this planet, but there could potentially
be liquid water at high pressures below it.
As instruments and techniques become sensitive enough to find and study planets that are
farther from their stars, many more of these water worlds may be found in the future.
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