Ganymede, Jupiter's largest moon, hosts the largest ocean of liquid water in the solar system beneath its icy crust. To understand its formation and internal composition, we must decipher the clues on its surface. The James Webb Space Telescope reveals new details about the texture and composition of Ganymede's surface components. Ganymede in the foreground. Illustration image Pixabay
Spectra taken with the NIRSpecet MIRI instruments at infrared wavelengths confirm that the surface is quite rough and that the first few micrometers of thickness are generally porous and consist mostly of crystalline water ice. Polar regions are covered with more water ice, especially in amorphous form, a phase in which H2O molecules are disordered.
These peculiar properties of polar ice could be explained by the bombardment of particles from Jupiter's magnetosphere, which is more intense at the poles than at the equator due to Ganymede's magnetic field. This bombardment also leads to the decomposition of H2O and the formation of new molecules such as hydrogen peroxide (H2O2), which was first detected in the polar regions. On the far side of Ganymede, the land on the eastern edge appears to be covered in morning frost that solidifies as the day progresses. Finally, carbon dioxide (CO2) appears to be trapped in minerals or salts on the surface at low latitudes and in water ice at high latitudes. It could be caused by the decomposition of organic molecules.
Despite the low temperatures between -180 and -110 ° C and the absence of a dense atmosphere, the surface of Ganymede therefore experiences chemical transformations and possibly diurnal fluctuations. This information will help optimize the operations of the European Space Agency's (ESA) JUICE spacecraft, which will be launched into orbit around Ganymede in 2034.
Example maps of the properties of water ice (H2O) and carbon dioxide (CO2) on the surface of Ganymede. They were carried out using data from the NIRSpec instrument, which is equipped with the James Webb Space Telescope.
© Bockelée-Morvan et al., 2023
Reference:
D. Bockelée-Morvan et al., Composition and thermal properties of the surface of Ganymede from JWST/NIRSpec and MIRI observations, A&A, 2023.
Samantha K. Trumbo et al., Hydrogen peroxide at the poles of Ganymed.Sci. Adv.9,eadg3724(2023).