Europa Contagion by Nicholas Thorp

The first crewed mission to Jupiter had been a complete success. After a five-year trip to the huge gas giant, the eight-person crew made the icy satellite Europa their new home. With three crew members exploring Europa's big brother, Ganymede, the remaining five astronauts stay on Europa to continue studying the one body in our Solar System that seems to offer the greatest hope of finding life. Daring hazards that humans have never-before encountered, the Europa team seeks to understand the enigmatic, dangerous little world that seems familiar and yet alien, at the same time. Extensive in situ exploration and research above and below the surface lead the Europa team members to encounter a peculiar anomaly. Investigation leads to humanity's greatest discovery. Or, perhaps, its worst nightmare.