JUNO spacecraft detects organic compounds on Ganymede


NASA‘s JUNO spacecraft detected salts and organic compounds on the surface of Ganymede, Jupiter‘s largest moon. Detection was made during a flyby in June 2021 when JUNO analyzed Ganymede using its Jovian InfraRed Auroral Mapper spectrometer (JIRAM).

The instrument is designed to study the chemistry and interactions within Jupiter’s atmosphere and those of its moons. Ganymede, the largest moon in the Solar System and even bigger than Mercury, has a vast ocean beneath its icy crust.

Organic substances at the equator

During its flyby of Ganymede in 2021, the JIRAM instrument detected salts like sodium chloride, as well as ammonium chloride, sodium bicarbonate, and, notably, organic compounds. The discovery of these substances will aid astronomers in understanding how Ganymede formed and may shed light on the chemical composition of its subterranean ocean.

Jupiter, being nearby, has such a strong magnetic field that organic compounds and salts on the surfaces of its Jovian moons would struggle to survive. However, the region around Ganymede’s equator appears to be sufficiently shielded from Jupiter’s magnetic field to support these compounds.

“We found the highest abundance of salts and organic materials in the dark and bright terrains at latitudes shielded from the magnetic field” said Scott Bolton, Juno’s principal investigator. “This suggests we are seeing the remnants of a deep, salty ocean that has reached the surface”.

This discovery is not necessarily related to life

The presence of these organic compounds, detected by JUNO, could indicate the presence of hydrothermal activity beneath Ganymede ‘s icy surface. Alternatively, they might be interactions between its subterranean ocean and the rocks in the planet’s depths.

“Extensive water-rock interaction could reach an equilibrium and is also consistent with the presence of sodium salts as indicators of aqueous alteration within Ganymede” the authors wrote in an article published in the journal Nature Astronomy on October 30th (ref.).

However, there could be other processes that created these salts besides the activity of a salty internal ocean, the authors add. “Since Ganymede has a substantially thicker crust than Europa, exchanges between the interior and the surface may not be responsible for its surface composition. They may instead reflect exchanges between the surface crust and the exterior, or exogenous deposition”.

JUNO was launched from Cape Canaveral, Florida, on August 5, 2011. It is the second mission to orbit Jupiter after NASA’s Galileo spacecraft. JUNO is designed to study the climate, magnetic environment, and history of the gas giant. The spacecraft’s mission has been extended twice and is currently expected to remain operational until September 2025.

Stefano Gallotta
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