In findings that underscore how common water is in our solar system, a team involving a Michigan Engineering researcher has detected a salty underground ocean on a moon of Jupiter.
Using NASA’s Hubble Space Telescope, the researchers confirmed previous results that suggested the satellite Ganymede might hold a buried sea.
The ocean is thought to have more water than all the water on Earth’s surface. Identifying liquid water is crucial in the search for habitable worlds beyond Earth and for the search of life as we know it, according to a NASA news release.
“A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth,” John Grunsfeld, associate administrator of NASA’s Science Mission Directorate at NASA Headquarters said.
In addition to Earth and Mars, water has been detected on at least two moons of Jupiter and two of Saturn’s.
Ganymede is the largest moon in our solar system and the only moon with its own magnetic field. The magnetic field causes aurorae, which are ribbons of glowing, hot electrified gas, in regions circling the north and south poles of the moon. Because Ganymede is close to Jupiter, it is also embedded in Jupiter’s magnetic field. When Jupiter’s magnetic field changes, the aurorae on Ganymede also change, “rocking” back and forth.
By watching the rocking motion of the two aurorae, scientists were able to determine that a large amount of saltwater exists beneath Ganymede’s crust affecting its magnetic field.
Xianzhe Jia, an assistant research scientist in the U-M Department of Atmospheric, Oceanic and Space Sciences, developed a global simulation model to help scientists understand the plasma and magnetic environment surrounding Ganymede.
“Using the simulation model we demonstrated that there is a measurable difference in the amplitude of the wobbling of the auroral oval as the moon is sailing through the giant Jovian magnetosphere when there is an ocean buried underneath the surface or not,” Jia said. “By comparing the Hubble observations of the aurora with our model predictions, we found that a sub-surface salty ocean best explains the wobbling of the moon’s aurora oval observed by the Hubble Space Telescope.”
Scientists estimate the ocean is 60 miles thick – 10 times deeper than Earth’s oceans – and is buried under a 95-mile crust of mostly ice, NASA says.
Scientists first suspected an ocean in Ganymede in the 1970s, based on models of the large moon. NASA’s Galileo mission measured Ganymede’s magnetic field in 2002, providing the first evidence supporting those suspicions. The Galileo spacecraft took brief “snapshot” measurements of the magnetic field in 20-minute intervals, but its observations were too brief to distinctly catch the cyclical rocking of the ocean’s secondary magnetic field.
The new observations were done in ultraviolet light and could only be accomplished with a space telescope high above the Earth’s atmosphere, which blocks most ultraviolet light.
Jia is co-investigator on three instrument teams of the joint mission by the European Space Agency and NASA, Jupiter Icy Moon Explorer (JUICE). JUICE will send a spacecraft to the Jupiter system to characterize the habitability of the Galilean satellites. One of the main science goals of the JUICE mission is to characterize the interior structure and particularly the subsurface ocean of Ganymede, Jia said. Juice’s launch is planned for 2022, with arrival in 2030.
Hubble is a project of international cooperation between NASA and 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 science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.
Story adapted from NASA’s news release.