Many worlds in our solar system show evidence of water, often locked beneath ice, but Earth remains the only known body with abundant, stable liquid water on its surface.
Subsurface oceans beyond Earth
Several icy moons, notably Jupiter’s moon Europa, are believed to harbour global subsurface oceans beneath thick ice shells, making them prime targets for astrobiology and future exploration missions that seek environments where liquid water and energy sources might support life.
What makes Earth unique
Earth’s position in the Sun’s habitable zone, combined with sufficient atmospheric pressure and temperatures, allows liquid water to persist at the surface in large, stable bodies such as oceans, lakes and rivers, a condition not observed on other planets or moons in our solar system.
Other moons with water evidence
In addition to Europa, Saturn’s moon Enceladus shows strong evidence for a subsurface ocean and active plumes that eject water vapour and ice into space, indicating a watery interior that interacts with the surface and space environment.
Water and ice on Mars
Mars preserves multiple lines of evidence for water in its past and present, including extensive polar ice caps and growing detection of buried or surface ice deposits that inform studies of the planet’s climate history and present habitability potential.
Significance for life and exploration
That Earth alone combines surface liquid water with temperate conditions and an energy budget suitable for complex chemistry explains why it is uniquely hospitable to the diverse life forms we observe and why locating liquid water elsewhere is central to the search for extraterrestrial life and future robotic and human missions.