Hubble Finds First Evidence of Water Vapor on the Solar System’s Largest Moon

Two decades of observations by the Hubble Space Telescope revealed evidence of the presence of water vapor in the thin atmosphere of Ganymede, Jupiter’s icy moon.

It is the largest moon in the Solar System, and it is believed that contains more water than all the oceans on Earth. But temperatures are so low that the surface water freezes, and the liquid ocean is suggested to lie about 100 miles below the ice crust.

At the same time, the water vapor discovered most likely did not come from that subterranean ocean. Scientists believe that it is the ice on the moon’s surface that is releasing the vapor. That is, it is formed when the ice on the surface goes from a solid state directly to a gaseous one.

The discovery contributes to a more complete understanding of Ganymede’s atmosphere, where previously only hints of oxygen had been found.

“Until now, only molecular oxygen had been observed [en la atmósfera de Ganímedes]. This occurs when charged particles erode the surface of the ice. The water vapor we measure now originates from the so-called sublimation of ice caused by thermal escape of water vapor from warm icy regions “, Explain Lorenz Roth of the Royal Institute of Technology in Stockholm, Sweden.

In 1998, the Hubble spectrograph took the first ultraviolet images of Ganymede, which revealed the presence of molecular oxygen and provided further evidence that the moon has a weak magnetic field.

Ganymede showed bands of auroras that are somewhat similar to the ovals of auroras seen on Earth and other planets with magnetic fields. However, some observed characteristics did not coincide with the expected emissions of a pure oxygen atmosphere, so the scientists suggested that this difference would be related to higher concentrations of atomic oxygen.

So Roth and his team analyzed the data files gathered by Hubble to measure the amount of atomic oxygen and found that there was hardly any atomic oxygen In the atmosphere of this frozen world So the scientists found another explanation for these discrepancies: Ganymede’s surface temperature varies greatly throughout the day, and around noon near the equator it can get hot enough that the ice surface releases (or sublime) tiny amounts of water molecules.

The new analysis found that differences in the ultraviolet aurora correlate with warming Ganymede’s surface during the day, exactly when water vapor would be released into the atmosphere. The results of the new research were published in the journal Nature Astronomy.

According to Roth, the new findings on Ganymede can provide valuable information for ESA’s next mission, JUICE, which will be devoted to detailed observations of Jupiter and three of its largest moons. The mission is scheduled to launch in 2022 and its arrival on Jupiter in 2029. Ganymede was selected for detailed research because it represents a natural laboratory for analyzing the nature, evolution, and potential habitability of icy worlds.

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