The discovery, which has been theorized for a long time, was made after observing movements of Ganymede’s aurora – shafts of light created by its poles. When the motion of the auroras – which is changed by both Jupiter’s and Ganymede’s magnetic fields – seemed to be damper than calculations would predict it to be, it left the existence of an underground water mass as the only explanation for this.
“I was always brainstorming how we could use a telescope in other ways,” Joachim Saur, geophysicist and team leader of the new finding, said in a statement. “Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon’s interior” stated NASA director of planetary science Jim Green today.
Ganymede is largest moon in the Solar System and the only one known of having its own magnetic field, being famously discovered by Galileo Galilei in 1610. Evidence mounted up in recent years to support the theory that it has water beneath its frozen surface, starting from the Galileo probe that measured its magnetic field almost 13 years ago. NASA planetary observers also said that Ganymede has certain remnants on its surface that might pertain from past floods.
Jupiter’s moons are starting to become an attractive target for future in depth observation, as their icy surface format might prove the existence of water in at least one of the other three moons. This particular discovery might prove important in the future due to the methodology it followed: further planets or satellites might be probed for the presence of water by the same auroras-based observation. The future could also see physical probes sent to the moons, as both NASA and the European Space Agency plan to explore them in the 2020’s.
Image Source: NASA