The oceans on Earth spread wide. They cover more than two‐thirds of our planet and drop nearly 10 kilometers deep. Out in space, scientists find alien worlds called Hycean planets. These water worlds hold clues in the search for life.

What Are Hycean Planets?

Hycean planets are heavy worlds. Their weight can reach ten times that of Earth. They keep most of their mass as water – up to 90%. Their oceans may stretch hundreds or thousands of kilometers deep. They hold a thick, hydrogen-rich air. That heavy layer traps heat and builds pressure on the surface. Liquid water can persist even when the heat nears 200°C, double the boiling point on Earth. High pressure stops water from boiling away. On the surface, the heat and squeeze would kill humans. But below the thick air, the oceans may stay in states we recognize. In the deepest parts, pressure may turn water into strange ice like ICE V. Such ice makes the planet’s inner layers very different from Earth.

Varieties of Hycean Worlds

Hycean worlds show up in many forms. Some lock to their stars. One side always faces the star while the other stays dark. On these dark planets, only the night side may stay cool enough for life. Some Hycean planets receive little sunlight. Their own warmth and heavy air keep vast oceans liquid.

Hycean planets also have a wide space where water can stay liquid. Their thick air and deep seas help them keep these conditions. They are top targets when we look for life on other planets.

The Abundance and Accessibility of Hycean Planets

Studies show that Hycean planets are very common in space. They may outnumber gas giants and rocky worlds. Their large size and heavy air make them easier for our telescopes to spot. This increases the chance of finding life signs in their air or on their surface.

One example is K2-18b. Its weight and orbit hint at a Hycean nature. Scientists recently found water vapor in its air. This news has raised excitement among researchers. Soon, the James Webb Space Telescope will check K2-18b’s air closely. That effort aims to add new facts about these watery worlds.

Life in the Depths: What Could Extraterrestrial Life Look Like?

If life grows on Hycean planets, it will seem very different from Earth’s plants and animals. Extreme heat, pressure, and a unique mix of chemicals point to the likelihood of tiny, microbial life. Such life forms may act like Earth’s extremophiles. They survive high heat and pressure and live in heavy air, where hydrogen holds sway over nitrogen or oxygen.

The many types of Hycean planets make us wonder even more. Perhaps huge sea animals roam their deep waters. They would not know air or bright skies. Life in these oceans might be very strange.

Reflecting on Our Place in the Cosmos

The chance that life exists deep in Hycean worlds makes us value our view here on Earth. We see vast oceans and clear skies that show the universe beyond. Hunting for life on water worlds like Hycean planets leads us to think of all that might be out there. It reminds us that our little world is part of a much broader, mysterious space.