Astronomers have discovered traces of water vapor in the atmosphere of Jupiter’s moon Ganymede for the first time. When ice on the moon’s surface sublimates (turns from solid to gas), water vapor is formed.
The discovery, which was published in the journal Nature Astronomy, was made using new and archival records from NASA’s Hubble Space Telescope.
Previous study has suggested that Ganymede, the solar system’s largest moon, has more water than the world’s oceans combined. However, the temperatures are so low that water on the surface has solidified. Ganymede’s ocean would be around 100 miles beneath the crust, therefore the water vapor would not represent the ocean’s evaporation.
To locate this evidence of water vapor, astronomers re-examined Hubble images from the last two decades.
The first ultraviolet (UV) photographs of Ganymede were taken in 1998 by Hubble’s Space Telescope Imaging Spectrograph (STIS), which revealed colorful ribbons of electrified gas termed auroral bands in two images and offered more evidence that Ganymede has a weak magnetic field.
The existence of molecular oxygen explained the parallels in these UV measurements (O2). However, some of the reported characteristics did not match those expected from a pure O2 environment. At the same time, experts decided that the divergence was most likely due to increased atomic oxygen concentrations (O).
Lorenz Roth of the KTH Royal Institute of Technology in Stockholm, Sweden, led the team that used Hubble to estimate the amount of atomic oxygen as part of a broad observing program to support NASA’s Juno mission in 2018. Hubble’s Cosmic Origins Spectrograph (COS) data from 2018 and archival photos from the Space Telescope Imaging Spectrograph (STIS) from 1998 to 2010 were integrated in the team’s research.
They were surprised to find that, contrary to previous interpretations of the data from 1998, there was very little atomic oxygen in Ganymede’s atmosphere. This implies that the apparent differences in these UV aurora photos must have a different explanation.
The relative distribution of the aurora in the UV photos was then examined by Roth and his team. The surface temperature of Ganymede changes dramatically throughout the day, and around noon near the equator, it may reach sufficiently warm that some water molecules are released (or sublimated) from the ice surface. In fact, where water would be expected in the moon’s atmosphere is directly associated with the perceived changes in UV images.
“Until now, only molecular oxygen had been discovered,” Roth explained. “When charged particles erode the ice surface, this occurs. The water vapor we’re measuring currently comes from ice sublimation, which is generated by water vapor thermally escaping from warm icy regions.”
This discovery raises the stakes for the European Space Agency’s forthcoming JUICE mission, which stands for Jupiter ICy Moons Explorer. JUICE is the first of ESA’s Cosmic Vision 2015-2025 program’s large-class missions. It will take at least three years to do thorough investigations of Jupiter and three of its major moons, with a focus on Ganymede as a planetary body and potential habitat. It will launch in 2022 and arrive at Jupiter in 2029.
Ganymede was chosen for further study because it serves as a natural laboratory for studying the nature, evolution, and potential habitability of icy worlds in general, as well as the role it plays within the Galilean satellite system and its unique magnetic and plasma interactions with Jupiter and its surroundings.
“Our findings can provide vital information to the JUICE instrument teams, which they can utilize to adjust their observation plans and maximize the spacecraft’s utility,” Roth noted.
Ganymede is now being studied by NASA’s Juno spacecraft, which recently published new images of the icy moon. Since 2016, Juno has been researching Jupiter and its surroundings, often known as the Jovian system.
Understanding the Jovian system and unraveling its history, from its beginnings to the appearance of potentially habitable habitats, would help us better comprehend how gas giant planets and their satellites arise and evolve. In addition, new information about the habitability of Jupiter-like exoplanetary systems should be discovered.
NASA and the European Space Agency collaborated on the Hubble Space Telescope (European Space Agency). The telescope is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Hubble science operations are managed by the Space Telescope Science Institute (STScI) in Baltimore, Maryland. The Association of Universities for Research in Astronomy in Washington, D.C. manages STScI for NASA.