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Using data from NASA’s Hubble and Spitzer
Space Telescopes, astronomers have found evidence

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that two exoplanets orbiting a star 218 light-years
away are “water worlds,” where water makes

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up a large fraction of the entire planet.

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The planetary system, known as Kepler-138,
have worlds that are unlike any planets in

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our own solar system.

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Astronomers didn’t directly detect water
on the Kepler-138 planets.

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Instead, they compared the planets’ sizes
and masses to models that concluded up to

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half of their volume should be made of materials
lighter than rock but heavier than hydrogen

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or helium.

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The most common of these materials is water.

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It is the best evidence astronomers have ever
found for water worlds, a type of planet long

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theorized.

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Researchers caution that the planets may not
have surface oceans like on Earth.

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The temperature of one planet’s atmosphere
is likely above the boiling point of water.

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They expect a thick, dense atmosphere made
of steam on this planet, but there could potentially

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be liquid water at high pressures below it.

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As instruments and techniques become sensitive
enough to find and study planets that are

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farther from their stars, many more of these
water worlds may be found in the future.

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