Coffee Breath

Europa (left) Ganymede (right) Jupiter’s moons By studying the subtle shifts of aurorae on Ganymede, scientists working with the Hubble Space Telescope have concluded that Jupiter’s largest moon hosts a massive subterranean ocean. Quite suddenly, the outer reaches of our solar system appear to be a very wet place, indeed. Ganymede, in addition to being the largest moon in the solar system (its radius is 0.413 Earths), is also the only moon to feature its own magnetic field. This magnetic field gives rise to aurorae, bands of hot electrified gas which circle the moon’s atmosphere and northern and southern poles. Oceans change the behavior of aurorae. If there was no ocean on Ganymede, the aurorae would rock back and forth across about six degrees of the moon’s circumference as it orbited Jupiter. The presence of a salty, electrically conductive ocean locks the aurorae in a much more stable position was detected. While the Hubble telescope made its observations in the UV spectrum, casting the aurorae in blue, they would actually appear red if you were to stand on the surface. The ocean under Ganymede’s crust is likely around 100 miles below the surface, which would make it complicated to study with a robot. Even if a space agency found a way to reach that far down, it’s thought that layers of ice separate the ocean from the surface. That means Ganymede is less than ideal for life, because it probably lacks a hydrothermal system like the one thought to exist on Enceladus. Because of these similar studies conducted on Europa and Enceladus, hypotheses arose proposing that heat from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics

Pan’s Labyrinth (via wordsthat-speak)