Enceladus

A small, shining moon

Enceladus is only about 500 km across, small enough to fit inside the UK, yet it is one of the most exciting places in the solar system. Its surface of fresh ice reflects almost all the sunlight that hits it, making it one of the brightest objects we know.

The tiger stripes

In 2005, NASA's Cassini spacecraft discovered jets of water vapour and ice grains erupting from four long fractures near the south pole, nicknamed tiger stripes. These plumes shoot material far into space, and much of it ends up in Saturn's faint E ring.

The jets are powered by tidal heating as Saturn's gravity flexes the moon, and they point to a global ocean beneath the ice.

Tasting the ocean

Cassini flew directly through the plumes several times, sampling them with its instruments. It detected salts, silica particles that suggest hot water reacting with rock, and molecular hydrogen, a possible energy source for microbes. Later analysis of Cassini data also found phosphates, an important ingredient for life as we know it.

Together, these findings make Enceladus one of the top places to search for life beyond Earth.

What comes next

Scientists have proposed missions that would orbit Enceladus or land near the tiger stripes to analyse fresh plume material. ESA has studied a large mission to Enceladus for the 2040s. Until then, Cassini's data, gathered before the spacecraft ended its mission in 2017, remains the best evidence we have.

Why scientists are so excited

Very few places in the solar system offer free samples of a hidden ocean. On Europa, any plumes are faint and uncertain, but on Enceladus the spray is constant and strong, so a spacecraft can simply fly through it and analyse what comes out. That is why many researchers rank Enceladus as one of the best places to look for life, and why mission planners keep coming back to it.

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