Ganymede and Europe are covered by thick crusts of ice and below that it is believed that there are huge, enclosed seas. The presence of water usually means a condition for life.
Researchers at the Royal Institute of Technology (KTH) in Stockholm have in recent years compared various observations of the moons made by the Hubble Space Telescope several years apart.
The original idea was to measure how much atomic oxygen there was in Ganymede’s atmosphere, but this led instead to the conclusion that there is a persistent amount of water vapor.
Ganymede is the largest moon in our solar system and its ninth largest celestial body. Researchers have previously estimated that its inland oceans contain more water than all of Earth’s oceans.
The surface temperature is around 160 degrees below zero. But for a time each day, it rises enough at the moon’s equator for the ice to release a small amount of water molecules, which change from solid to steam.
The KTH researchers’ discovery was published in the scientific journal Nature Astronomy this summer and after that they went on to take a closer look at Europe.
Europe is slightly smaller than the earth’s moon. It has previously been noted that there are a kind of giant geysers on its solid and icy surface, where evaporated water from the moon’s interior is ejected.
When comparing Hubble observations, the researchers found that the amount of water was widespread and persistent over time – albeit in one of Europe’s hemispheres, that which faces “backwards” in the moon’s bound rotation around Jupiter. Why it is so unevenly distributed is not yet known. The findings have been published in Geophysical Research Letters.
“The observations of water vapor on Ganymede and on the back of Europe take us further in our understanding of the atmospheres of the ice moons,” said Lorenz Roth, an astronomer who has led the research at KTH, in a press release European Space Agency Esa went out with on Thursday.
The findings can be added to Esa’s forthcoming exploration project where three of Jupiter’s four so-called Galilean moons will be explored. The space probe Juice (Jupiter Icy Moons Explorer) is scheduled to be launched next summer. It will travel for just over seven years before it can orbit the giant gas planet and study Ganymede, Europe and Callisto.
American Nasa is planning a mission in the same area, where the probe Europa Clipper will examine Europe and investigate the conditions for life and probe a possible landing site for the future.
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