Sub-Neptune planets, often billed as possible "water worlds," may be more desert than deep sea, according to a new study.

For years, scientists thought these planets, which are larger than Earth but smaller than Neptune, could form far from their stars, sweeping up ice beyond the so-called "snow line." As the planets migrated inward, scientists have thought that ice might melt into oceans hidden beneath hydrogen skies. Such hypothetical worlds were dubbed "Hycean planets," a blend of "hydrogen" and "ocean."

"Our calculations show that this scenario is not possible," Caroline Dorn, an assistant professor of Physics at ETH Zürich in Switzerland who co-led the new study, said in a statement.

The results come just months after high-profile claims about K2-18b, an exoplanet about 124 light-y

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