Paganini and his team reported in the journal Nature Astronomy on November 18 that they detected enough water releasing from Europa (5,202 pounds, or 2,360 kilograms, per second) to fill an Olympic-size swimming pool within minutes. Yet, the scientists also found that the water appears infrequently, at least in amounts large enough to detect from Earth, said Paganini: “For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method.”Animation of water molecules at EuropaWater molecules emit specific frequencies of infrared light as they interact with solar radiation.Credits: Michael Lentz/NASA GoddardIndeed, Paganini’s team detected the faint yet distinct signal of water vapor just once throughout 17 nights of observations between 2016 and 2017. Looking at the moon from the W. M. Keck Observatory atop the dormant Mauna Kea volcano in Hawaii, the scientists saw water molecules at Europa’s leading hemisphere, or the side of the moon that’s always facing in the direction of the moon’s orbit around Jupiter. (Europa, like Earth’s moon, is gravitationally locked to its host planet, so the leading hemisphere always faces the direction of the orbit, while the trailing hemisphere always faces in the opposite direction.)