Reviewing the images of Ganymede’s aurora, the team discovered that, as the moon’s surface temperature rises and falls throughout the day, it becomes warm enough around noon near the equator for sublimation to occur, releasing water molecules.

“In a wider sense, this discovery shows that often one needs to know what to focus on when analyzing data. The signal from H2O was present in the HST images since 1998,” said lead author Lorenz Roth. “Only with additional information through new data and predictions from theoretical studies, we knew what to look for and where to search for it. There are likely many more things to discover in the gigantic dataset that the Hubble Space Telescope has accumulated over its three decades in space.”

Where there’s water, there could be life as we know it. Astronomers say that finding liquid water beyond Earth is crucial in our hunt for other habitable worlds.