This water vapor is formed when the ice on the surface instantly changes from solid to gas.
Jupiter’s moon Ganymede is a special specimen. Ganymede is not only the largest moon in our solar system – and even larger than the planet Mercury – which scientists suspect harbors a true subterranean ocean beneath its icy crust. In a new study, researchers take a closer look at the largest moon in our solar system. And this leads to an unusual discovery: for the first time, astronomers have found evidence of water vapor in its atmosphere.
Previous research has shown that Ganymede may contain more water than all of Earth’s oceans combined. However, it is so cold on the Moon that the water on its surface freezes. So Ganymede’s ocean would be hiding under the crust 100 miles (160 km) deep. While you might think that the newly discovered water vapor comes from this ocean, it turns out that it is not. The researchers discovered that there was something else behind it.
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In 1998, the Hubble Space Telescope produced for the first time ultraviolet images of Ganymede. Astronomers have discovered colorful streaks of electrified gas, somewhat similar to the aurora borealis on Earth. According to the research team at the time, this indicated that molecular oxygen (O2) could be found in the lunar atmosphere. However, there are other features that have been noted that conflict with this. The scientists eventually concluded that this startling discrepancy was probably related to higher concentrations of atomic oxygen (O).
in a The new study Researchers have sometimes wanted to know how much atomic oxygen is in Ganymede’s atmosphere. For this, they again used the data from the Hubble Space Telescope collected over the past 20 years. To their surprise, and contrary to the original interpretations of the data in 1998, the new research team found no atomic oxygen in Ganymede’s atmosphere. This means that there must be another explanation for the aforementioned discrepancy.
The researchers took a closer look at the images produced by Hubble. This led to an interesting discovery. Ganymede’s surface temperature is known to vary widely during the day. At noon, near the equator, it can get so hot that the surface of the ice sublimates – that is, it instantly turns from solid to gas. This causes the formation of water vapor. So the researchers hypothesize that this water vapor may explain the discrepancy. The differences observed in the UV images are directly related to the parts of the atmosphere where water vapor is expected.
This means that in the meantime we get a better picture of Joe Ganymede. “So far, only molecular oxygen has been discovered,” said study researcher Lorenz Roth. This forms when charged particles erode the surface of the ice. The water vapor we have now measured arises from sublimation of ice in warmer regions.”
The findings are particularly important for the European Space Agency’s upcoming mission to Jupiter. This mission is scheduled for 2022 and will then reach the gas giant in 2029. The mission (named Juice) will investigate Jupiter’s atmosphere and magnetic fields. But what’s even more interesting is that it takes a look at Jupiter’s icy moons Ganymede, Europa and Callisto. Researchers are particularly interested in Ganymede, in part because the subterranean ocean mentioned above may be fertile ground for (microscopic) life. “Our results can provide the mission team with valuable information that can be used to improve their observation plans and improve their spacecraft,” Roth concludes.
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