Scientists discover water vapor in atmosphere of Jupiters largest moon

Astronomers for the first time detected water vapor in the atmosphere of Jupiter’s largest moon, Ganymede, NASA announced Monday.

Scientists made the discovery by examining new and old data from NASA’s Hubble Space Telescope from the last two decades, and published their findings in the journal Nature Astronomy.

Ganymede, the largest moon in the solar system, has more water than all of Earth’s oceans, previous research has found. But temperatures there are so cold that water on the moon’s surface is frozen solid, and the moon’s ocean is about 100 miles below the icy crust, according to NASA.

The water vapor discovered, therefore, could not be from evaporation of the underground ocean but from ice vaporizing from Ganymede’s surface, scientists theorize.

The Hubble telescope, which astronomers used when it discovered water vapor, took the first ultraviolet images of Ganymede in 1998 and picked up the presence of molecular and atomic oxygen.

Lorenz Roth of the KTH Royal Institute of Technology in Stockholm, Sweden, led a NASA team to measure the amount of atomic oxygen with the Hubble telescope in 2018, studying data from 1998 to 2010, and instead revealed the presence of water vapor.

While the scientists found hardly any atomic oxygen in Ganymede’s atmosphere compared to data from 1998, they learned that the surface temperature varies widely throughout the day and could become warm enough around noon for the ice surface to release some small amounts of water molecules.

“So far only the molecular oxygen had been observed,” Mr. Roth told NASA. “This is produced when charged particles erode the ice surface. The water vapor that we measured now originates from ice sublimation caused by the thermal escape of water vapor from warm icy regions.”

NASA’s Juno mission is studying Ganymede and new images of the icy moon. In June, the Juno spacecraft zipped past Ganymede for the first close encounter with the celestial body since Galileo flew by it back in May 2000.

The flyby not only snapped photos of the moon, but also will allow scientists to learn about the moon’s composition, ionosphere, magnetosphere and ice shell, NASA said. The spacecraft also will measure the radiation environment near Ganymede.

Juno will return for closer looks at Jupiter’s other large moons including Europa next year and Io after that.

Since 2016, Juno has been studying Jupiter and its environment, also called the Jovian system.

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