Title: NASA’s Juno Mission Finds Evidence of Briny Past on Jupiter’s Moon Ganymede
Subtitle: Spectrometer onboard Juno spacecraft reveals mineral salts and organic compounds on Ganymede
Date: October 30, 2023
In a groundbreaking discovery, NASA’s Juno mission has provided evidence of a briny past on Ganymede, Jupiter’s largest moon. The Jovian InfraRed Auroral Mapper (JIRAM) spectrometer aboard the spacecraft collected data during a close flyby of Ganymede, revealing mineral salts and organic compounds on the moon’s surface. These findings, published in the journal Nature Astronomy, could shed light on the origin of Ganymede and the composition of its deep ocean.
Ganymede, larger than the planet Mercury, has always intrigued scientists due to its hidden internal ocean of water beneath its icy crust. Previous observations from NASA’s Galileo spacecraft and Hubble Space Telescope, along with the European Southern Observatory’s Very Large Telescope, hinted at the presence of salts and organics on Ganymede. However, the resolution of those observations was too low to confirm these findings.
On June 7, 2021, the Juno spacecraft flew over Ganymede at a minimum altitude of 650 miles (1,046 kilometers). During this close approach, the JIRAM instrument captured infrared images and spectra of Ganymede’s surface. The data, with an unprecedented spatial resolution for infrared spectroscopy, revealed unique spectral features of non-water-ice materials on the moon. These materials include hydrated sodium chloride, ammonium chloride, sodium bicarbonate, and possibly aliphatic aldehydes.
Lead author Federico Tosi, a Juno co-investigator from Italy’s National Institute for Astrophysics, explained that the presence of ammoniated salts suggests Ganymede may have accumulated materials cold enough to condense ammonia during its formation. The carbonate salts detected could be remnants of carbon dioxide-rich ices.
The study also revealed the importance of Ganymede’s magnetic field in protecting its equatorial region from the harmful effects of Jupiter’s magnetic field. Particle fluxes generated by Jupiter’s magnetic field negatively impact salts and organics. JIRAM’s observations focused on latitudes protected by the magnetic field, demonstrating the remnants of a deep ocean brine that reached the moon’s surface.
Juno’s mission extends beyond Ganymede. In October 2021 and September 2022, the spacecraft also observed Europa, another Jovian moon believed to have an ocean under its icy crust. Juno will continue its exploration with an upcoming flyby of Io, scheduled for December 30, 2023.
Managed by NASA’s Jet Propulsion Laboratory, the Juno mission is part of NASA’s New Frontiers Program. The Italian Space Agency funded the Jovian InfraRed Auroral Mapper, while Lockheed Martin Space built and operates the spacecraft.
This significant finding on Ganymede adds to our understanding of the complex Jovian system and paves the way for future missions to explore the intriguing secrets of Jupiter’s moons.
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