Water vapor on Ganymede

Soon, astronomers have located water vapor on Ganymede, the largest and most massive moon in the solar system, which orbits Jupiter. The discovery is a step toward understanding the habitability of satellites orbiting the giant planet. Noon near Ganymede’s equator is warm enough for some of the moon’s icy crust to sublimate. In other words, the ice goes from solid to gas, and water vapor is released.

This finding was made using archived and new data from the Hubble Space Telescope. The research outcomes were issued in the journal Nature Astronomy on July 26, 2021.

From 1998 and 2010, the Hubble Space Telescope marked Ganymede in ultraviolet light. Both observations revealed the presence of an auroral belt on Ganymede. This sign that this large moon has a permanent magnetic field created by its iron core. Ganymede orbits within Jupiter’s magnetic field. However, Ganymede’s auroral active region appeared to be different in 2010 than in 1998. This difference was thought to be due to atomic oxygen in Ganymede’s thin atmosphere.

Fast forward nearly a decade to 2018. A squad of astronomers guided by Lorenz Roth from the Royal Institute of Technology in Stockholm, Sweden, reviewed Hubble’s ultraviolet data. They used the old data and new data from Hubble’s instrument Cosmic Origins Spectrograph. The new data measured the amount of atomic oxygen in Ganymede’s atmosphere. The results showed that Ganymede has very little atomic oxygen. This overturned previous explanations for the differences in the ultraviolet aurora.

So Roth’s team took a closer look at where on Ganymede the ultraviolet aurora was occurring. That’s when they made an interesting discovery. The location of Ganymede’s aurora correlated with where water would be expected to be in Ganymede’s atmosphere if the moon were emitting water vapor,? Ross explains.

So far, only oxygen molecules have been observed. This occurs when charged particles erode the surface of the ice. The water vapor measured in this study comes from ice sublimation, which occurs when water vapor escapes from areas of warm ice due to heat.