Ocean Worlds

What are Ocean Worlds?

Earth is defined by its ocean, as the majority of our planet’s surface (>70%) is water. Earth’s ocean drives the water cycle that dominates our land and atmosphere. But Earth is not the only planet with an ocean. Ocean worlds are icy moons in our solar system that have liquid and solid water oceans: that is to say, oceans like the one found on our own planet, and icy oceans like those found on Europa and Enceladus. On Earth, the signal of life in the ocean is so strong that it can be seen from space. Remote sensing of ocean worlds is more challenging because the oceans are covered by thick layers of ice that obscure the liquid ocean below.

The Importance of Water Worlds

Life as we know it requires three ingredients: energy, organic molecules, and liquid water. Our search for life beyond Earth is a search for planets, dwarf planets, and moons that harbor substantial liquid water. We call these places “ocean worlds.”

We’re learning that ocean worlds could be ubiquitous in the galaxy. Just in our solar system, we have found evidence of oceans on Saturn’s moons Titan and Enceladus; Jupiter’s moons Europa, Ganymede, and Callisto; Neptune’s moon Triton; and on Pluto. We also believe that Venus and Mars may have had oceans billions of years ago. Could they have supported life?

Europa and Enceladus
Europa: The puzzling, fascinating surface of Jupiter's icy moon Europa looms large in this view made from images taken by NASA's Galileo spacecraft in the late 1990s.

Learn more: NASA/JPL-Caltech europa-facts
Enceladus: This mosaic of Saturn's moon Enceladus was created with images captured by NASA's Cassini spacecraft on Oct. 9, 2008, after the spacecraft came within about 16 miles (25 kilometers) of the surface of Enceladus.

Learn more: NASA/JPL/Space Science Institute

NASA’s research on oceans also includes our own planet and helps us to better understand the role of Earth’s ocean in our planet’s climate system. As we learn more about our own oceans, we will better understand worlds beyond Earth.

Learn more about Ocean Worlds in: Ocean Worlds: Planetary Oceans and Earth's Marine Ecosystems , an introductory exploration of planetary oceans and the significance of Earth's oceans, and Ocean Worlds Resources , a curated collection of resources, including activities that can be done at home, as well as videos, animations, printable graphics, and online interactives.