NASA Finds Water Vapor on Jupiter's Moon Ganymede for the First Time

The journey of the latest find dates back to 1998 when Hubble took the first UV image of Jupiter’s moon using its Imaging Spectrograph. The image featured colour aural bands colorful ribbons made by electrified gas similar to auroras or polar lights on Earth. The band revealed that Ganymede has a weak magnetic field. However, observation by Hubble showed that the auroral bands changed over time. The reason behind this, scientists thought, was the presence of molecular oxygen and single oxygen atoms in Ganymede’s atmosphere.

As oxygen atoms affect the wavelength of ultraviolet light, In 2018, when scientists tried to measure the amount of oxygen in Ganymede’s atmosphere, they were surprised as there were hardly any single oxygen atoms that could have caused the difference in the UV wavelength. Searching for other explanations that could explain such an observation, scientists combined all the data and analyzed spectral images and high-sensitivity spectra captured by Hubble, and they found evidence of water in the atmosphere. In fact, they also found that at a point where the sunlight directly hits the Jupiter moon, water vapor is more abundant than molecular oxygen.

“The water vapor that we measured now originates from ice sublimation caused by the thermal escape of water vapor from warm icy regions,” said Lorentz Roth, one of the authors of the study, in a statement.

According to scientists, the temperature on Ganymede varies widely throughout the daytime, making it really warm when the sun is overhead. This causes the ice to directly sublimate into water vapor instead of melting into liquid water. The study was published on July 26 in Nature Astronomy.

The study will help European Space Agency’s upcoming mission JUICE — JUpiter ICy moons Explorer, which aims to observe Jupiter’s moons for three years, especially Ganymede as potential habitat in the solar system.