NASA’s Juno spacecraft discovers evidence of a salty ocean on Jupiter’s biggest moon

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NASA’s Juno spacecraft, orbiting Jupiter since 2016, has recently turned its attention to the gas giant’s moons, uncovering groundbreaking findings on Ganymede, Jupiter’s largest moon.

Research published in Nature Astronomy reveals that Ganymede shows signs of salts and organic compounds on its surface, likely residues from a subsurface salty ocean. This discovery raises the exciting possibility that Ganymede’s conditions might be conducive to life.

Ganymede stands out in the solar system. Not only is it Jupiter’s most massive satellite, but it’s also larger than the planet Mercury, making it the biggest moon in the solar system. It’s unique for having its own magnetic field, generated by a molten metal core. Like other icy worlds in the outer solar system, Ganymede is believed to harbor an ocean beneath its icy crust, possibly comprising multiple layers of ice and water.

The University of Arizona geologist Adeene Denton, not affiliated with the study, notes that Ganymede’s massive size makes its interior structure more complex than smaller worlds. This complexity means that interesting molecules have a lot of space to mix but are harder to detect since they must travel a great distance to reach the surface.

Juno’s close approach to Ganymede, within 650 miles, allowed it to use its Jovian InfraRed Auroral Mapper (JIRAM) to analyze the moon’s surface composition in detail. This instrument can map features as small as 1 kilometer wide, providing unprecedented insights into Ganymede’s chemical makeup.

The presence of surface salts suggests a briny subsurface ocean, a condition considered necessary for habitability. Oceans typically acquire their salt from chemical interactions between liquid water and a rocky mantle. However, current research indicates that Ganymede’s ocean might not directly touch its mantle, with icy crusts acting as barriers. Despite this, the detection of salts implies that at some point in the past, the ocean and mantle were in contact.

The organic chemicals detected by Juno are still being analyzed, but they might be aliphatic aldehydes, a step towards forming complex amino acids. While not indicative of life, their presence is crucial for the potential of life in Ganymede’s hidden oceans.

This discovery by Juno is a unique opportunity to understand Ganymede, and further exploration is anticipated with the ESA JUICE mission, expected to provide comprehensive coverage of Ganymede in about ten years.

Reference(s): Research Paper(pdf)

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