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Using old and new data from the Hubble Space Telescope, researchers at NASA have found the first evidence of water vapor on Jupiter’s largest moon, called Ganymede. This water vapor likely forms through a process called sublimation—where ice turns directly into gas without entering a liquid form first.
Existing research has led some scientists to believe that Ganymede contains more water than all of Earth’s oceans. But the moon’s temperatures would freeze any water on the surface—any oceans on Ganymede would need to reside deep below the moon’s crust.
Yet, scientists found something strange when they took the first UV images of Ganymede in 1998. A pattern of auroral bands appeared, and they looked pretty similar to Earth’s aurora ovals. The UV patterns observed on Ganymede could indicate a permanent magnetic field and the presence of gaseous water, but until now, astronomers attributed the pattern to “atomic oxygen.”
New data from Hubble and the Juno orbiter led scientists to reassess their findings. It turns out that Ganymede’s surface temperature varies wildly throughout the day, and that its equator may get hot enough to sublimate frozen water around “noon.”
We should learn more information in the coming years. The European Space Agency plans to launch a Jupiter Icy Moons Explorer mission (JUICE) in 2022, and the explorer should arrive at the planet in 2029. If Ganymede really has a magnetic field and lots of water, then it could be habitable, so the ESA will pay special attention to it during the JUICE mission.