The Hubble Orbiting Telescope has detected for the first time traces of water vapor in the atmosphere of Ganymede, one of Jupiter's largest moons. Thanks to this, scientists suggested how exactly the atmosphere of this object could have formed. The research results were published in the scientific journal Nature Astronomy.
"The rarefied atmosphere of Ganymede is believed to have resulted from the constant evaporation of ice on its surface under the influence of sunlight and charged particles. However, observations have shown that there is oxygen in its atmosphere, but no water. We first found traces of it in the Hubble data." - the researchers write.
Scientists have known about the existence of a rarefied atmosphere in Ganymede for a long time: Hubble discovered its traces in 1998. In the vicinity of Ganymede, the telescope detected a large number of oxygen ions. Scientists assumed that its source was water molecules, which were knocked out of the satellite's ice shell by high-energy particles or sunlight. In the future, astronomers did not find a single trace of water in the atmosphere of Ganymede.
Astronomers led by Kurt Rutherford of the Southwestern Research Institute (USA) analyzed observational data for April 2018, when Ganymede was in the shadow of Jupiter for several hours. Comparing them with the data of "Hubble" of previous years, scientists "removed" the oxygen signal from the spectrum of Ganymede, thanks to which they saw "water" lines in the spectrum of the satellite. Previously, they were drowned out by a stronger signal from oxygen ions.
Thanks to this, scientists estimated the concentration of water in the atmosphere of Ganymede and measured its approximate mass. In addition, they found that the concentration of water vapor on the light and dark sides of the moon is very different. On the sunny side, there were about 30 nanograms for every square centimeter of the surface of Jupiter's moon, and on the reverse side it was not at all.
Rutherford and his colleagues hope that the European mission JUICE, which is planned to be launched into space next June, will reveal the reason for this.