From NASA
July 26, 2021
For the first time, astronomers have discovered evidence of water vapor in the atmosphere of Jupiter’s moon Ganymede. This water vapor forms when ice sublimes from the surface of the moon – in other words, it turns from solid to gaseous.
Scientists used new and archived datasets from NASA’s Hubble Space Telescope to make the discovery, which was published in the journal Nature Astronomy.
This image shows Jupiter’s moon Ganymede as seen by NASA’s Hubble Space Telescope in 1996. Ganymede is half a billion miles (over 600 million km) away, and Hubble can track changes on the moon and show other properties in the ultraviolet and near infrared wavelengths. Astronomers have now used new and archived records from Hubble to reveal, for the first time, evidence of water vapor in the atmosphere of Jupiter’s moon Ganymede, due to the thermal escape of water vapor from the moon’s icy surface.Credits: NASA, ESA, John Spencer (SwRI Boulder)
Previous research has suggested that Ganymede, the largest moon in the solar system, contains more water than any of the Earth’s oceans. However, the temperatures there are so cold that the water is frozen to the surface. Ganymede’s ocean would be about 160 miles below the crust; therefore the water vapor would not represent the evaporation of this ocean.
Astronomers re-examined Hubble’s observations over the past two decades to find this evidence of water vapor.
In 1998, Hubble’s Space Telescope Imaging Spectrograph took the first ultraviolet (UV) images of Ganymede, showing colored bands of electrified gas called aurora bands, providing further evidence that Ganymede has a weak magnetic field.
The similarities in these UV observations were explained by the presence of molecular oxygen (O2). However, some observed characteristics did not correspond to the expected emissions from a pure O2 atmosphere. At the same time, the scientists concluded that this discrepancy is likely related to higher concentrations of atomic oxygen (O).
As part of a large observational program in support of NASA’s Juno mission in 2018, Lorenz Roth of the KTH Royal Institute of Technology in Stockholm, Sweden, led the team that used Hubble to measure the amount of atomic oxygen. The team’s analysis combined data from two instruments: Hubble’s Cosmic Origins Spectrograph in 2018 and archive images from the Space Telescope Imaging Spectrograph (STIS) from 1998 to 2010.
To their surprise, and contrary to the original interpretations of the 1998 data, they found that there was little atomic oxygen in Ganymede’s atmosphere. This means that there must be some other explanation for the obvious differences in these UV aurora images.
Roth and his team then took a closer look at the relative distribution of the northern lights in the UV images. The surface temperature of Ganymede fluctuates greatly during the day and around noon near the equator it can get so warm that the ice surface releases (or sublimates) small amounts of water molecules. In fact, the perceived differences in the UV images correlate directly with where water would be expected in the lunar atmosphere.
In 1998, Hubble’s Space Telescope Imaging Spectrograph took these first ultraviolet images of Ganymede, which showed a particular pattern in the observed emissions from the lunar atmosphere. The moon shows aurora bands that are somewhat similar to the aurora ovals observed on Earth and other planets with magnetic fields. This was vivid evidence that Ganymede has a permanent magnetic field. The similarities in the ultraviolet observations were explained by the presence of molecular oxygen. The differences were explained at the time by the presence of atomic oxygen, which generates a signal that affects one UV color more than the other.Credits: NASA, ESA, Lorenz Roth (KTH)
“So far, only molecular oxygen has been observed,” explains Roth. “This occurs when charged particles erode the surface of the ice. The water vapor that we have now measured comes from the ice sublimation, which results from the thermal escape of water vapor from warm ice regions. “
This finding makes the upcoming mission of ESA (European Space Agency) JUICE, which stands for JUpiter ICy moons Explorer, excited. JUICE is the first large-scale mission under ESA’s Cosmic Vision 2015-2025 program. Scheduled to launch in 2022 and arrive at Jupiter in 2029, it will spend at least three years making detailed observations of Jupiter and three of its largest moons, with a particular focus on Ganymede as a planetary body and potential habitat.
Ganymede has been identified for detailed study as it is a natural laboratory for the analysis of the nature, evolution, and potential habitability of ice worlds in general, its role in the Galilean satellite system, and its unique magnetic and plasma interactions with Jupiter and its surroundings.
“Our results can provide the JUICE instrument teams with valuable information that they can use to refine their observation plans to optimize the use of the spacecraft,” added Roth.
Right now, NASA’s Juno mission is taking a close look at Ganymede and has recently released new images of the icy moon. Juno has been studying Jupiter and its surroundings, also known as the Jovian System, since 2016.
Astronomers used new and archived datasets from NASA’s Hubble Space Telescope to uncover evidence of water vapor in the atmosphere of Jupiter’s moon Ganymede. The steam is created by the thermal stimulation of water molecules from the icy surface of the moon. Previous research has shown that the moon contains more water than any of the oceans on earth. However, the temperatures there are so cold that the water freezes on the surface and the ocean is about 160 miles below the crust.Credit: NASA’s Goddard Space Flight Center
Understanding the Jupiter system and deciphering its history, from its origin to the possible creation of habitable environments, will give us a better understanding of how gas giant planets and their satellites form and evolve. In addition, hopefully new insights into the habitability of Jupiter-like exoplanetary systems will be gained.
The Hubble Space Telescope is an international cooperation project between NASA and the ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble research operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, DC
Media contact:
Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
Bethany Downer
ESA / Hubble.org
Contact science:
Lorenz Roth
KTH Royal Institute of Technology, Stockholm, Sweden Last updated: 07/26/2021 Editor: Lynn Jenner
Like this:
Loading…
Comments are closed.