For the first time: Hubble finds water on Jupiter’s moon Ganymede…..

For the first time, we have proof that water vapour is in the atmosphere of Jupiter’s moon Ganymede, which is the largest moon in the solar system. The frozen water on Ganymede’s surface may have sublimated, going from a solid to a gas without melting.

Ganymede’s surface has both dark, cratered areas and bright, grooved areas that make interesting patterns. Researchers have thought for a long time that Ganymede has a lot of water, maybe even more than Earth. But because Ganymede is so far from the Sun, the water could only stay liquid under a thick layer of ice.

Ganymede is thought to have three main layers: an iron core, a rocky mantle, and a layer of water that is both liquid and frozen. The ice shell on the outside is very thick (about 500 miles/800 km), and there could be liquid water underneath it. No matter what, there is water, and where there is water, there may be life.

Researchers have found water on the surface that is not frozen for the first time.

Lorenz Roth of the KTH Royal Institute of Technology in Stockholm, Sweden, was using Hubble to measure the amount of oxygen on Ganymede as part of a larger program of observations. Roth and his team used information from two telescopes: Hubble’s Cosmic Origins Spectrograph from 2018 and images from 1998 to 2010 from the Space Telescope Imaging Spectrograph (STIS).

In 1998, Hubble’s Space Telescope Imaging Spectrograph (STIS) took the first ultraviolet (UV) pictures of Ganymede. These pictures showed that the moon’s atmosphere was giving off light in a certain way. Auroral bands can be seen on the moon. They are similar to aurora ovals that can be seen on Earth and other planets with magnetic fields. This was an example of proof that Ganymede has a magnetic field that is always there. The presence of molecular oxygen explained why the ultraviolet observations were similar (O2). At the time, the differences were thought to be caused by atomic oxygen (O), which sends a signal that changes one UV color more than the other. Credit: NASA, ESA, and Lorenz Roth (KTH)

At least, that’s what the original interpretation from 1998 said about the UV data, which showed that atomic oxygen was there. But Roth’s team was very surprised to find almost no atomic oxygen in Ganymede’s atmosphere. If this is the case, there must be another reason why these UV aurora pictures look different.

When the scientists looked more closely at the UV images of the colored bands of charged gas called auroral bands, they found another piece of evidence: the surface temperature of Ganymede changes a lot during the day. Around noon, the equatorial parts of Ganymede may get warm enough that the ice surface gives off (or “sublimates”) a few water molecules.

This fits very well with what we know from Hubble. Around the equator, Roth found what he thought was oxygen but now thinks is water vapor.

“So far only the molecular oxygen had been observed,” explained Roth. “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”.

With the upcoming mission of the European Space Agency, this discovery makes Ganymede a much more interesting place. The JUICE (Jupiter ICy moons Explorer) spacecraft is set to take off in 2022 and land on Jupiter in 2029. The mission will spend three years studying Jupiter and its biggest moons, including Ganymede, in great detail.

“Our results can provide the JUICE instrument teams with valuable information that may be used to refine their observation plans to optimize the use of the spacecraft,” added Roth.

Compare the Earth, the Moon (at the top), and Ganymede (bottom).

Astronomers are looking at Jupiter and Saturn’s frozen moons more and more as places where life could start. They used to be thought of as barren, frozen wastelands, but the more we look at them, the more likely it seems that people could live on them. Even though Ganymede could have life, that doesn’t mean it does. That’s something that will have to be found out by more research.

Nature Astronomy wrote about the study.

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