Evidence of water vapor in the atmosphere of Jupiter's moon Ganymede

Evidence of water vapor in the atmosphere of Jupiter’s moon Ganymede

According to a research group at the Royal Institute of Technology in Sweden, as a result of analyzing the data observed by NASA’s Hubble Space Telescope, evidence of the existence of water molecules in the atmosphere of Ganimede was found.

Jupiter’s moon Ganymede has been investigated by various spacecraft since the observation by Pioneer 10 in 1972. For example, the Voyager program revealed the exact size of Ganymede, and a Galileo spacecraft mission carried out between 1996 and 2000 discovered that it had its own magnetic field and a large amount of water (sea) underground.

Spacecraft surveys and Hubble Space Telescope observations have also shown that the surface of Ganymede is covered with ice and that there is an atmosphere.

In 1998, the Hubble Space Telescope’s space telescope imaging spectrometer was used to capture the world’s first UV image of Ganimede.

When the ultraviolet images were analyzed, two “light patterns” indicating the atmospheric condition of Ganymede were observed, and it was thought that this difference was caused by oxygen molecules contained in the atmosphere.

At this time, another “light pattern” was observed that was caused by oxygen molecules, but it was speculated that it was due to the “oxygen atoms” contained in the atmosphere at that time.

However, when a research group at the Royal Institute of Technology of Sweden photographed the ultraviolet spectrum taken by the Hubble Space Telescope’s Cosmic Origins Spectroscope and examined how much oxygen atoms were contained compared to the previous data, is said that there were almost no oxygen atoms in the atmosphere.

Therefore, in order to investigate why different light patterns were observed, we analyzed the “relative distribution” of Ganymede’s aurora in detail. As a result, the place where the different light patterns were measured was said to coincide with “the place where the temperature of the ice covering the surface melts and sublimates”.

In other words, it was speculated that the atmosphere at that location contained water vapor from which ice had sublimated, so the “light pattern” that indicates the atmospheric condition was different.

Atmospheric conditions have a particular impact on observation equipment, so this discovery is expected to be of great help to future Ganymede exploration.

Ganymede, where air and water exist, is also an important place for space development, and JUICE (Jupiter ICy moons Explorer: Jupiter Exploration Mission), in which Japan is also participating, is planning to observe the surface and underground.

The spacecraft is scheduled to be launched in 2022, and is expected to reach Jupiter in 2029. We are paying attention to what kind of discoveries will be made in the future.