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On Sept. 21, 2003, the Galileo spacecraft plunged into Jupiter’s dense atmosphere, ending nearly a decade of studying the planet. More than 20 years after its mission ended and nearly 30 years since it arrived in Jupiter’s orbit, the NASA probe continues to reveal new insights thanks to data it sent back.
A new ocean world. A new study suggests Callisto is “most likely” an oceanic world—a rocky body covered by a layer of water that is at least partially liquid. The key to this discovery was a more comprehensive analysis of data from the Galileo mission, including its full set of magnetic measurements.
Callisto, the most distant of Jupiter’s four Galilean moons, is also its second largest. It’s roughly the size of Mercury but has significantly less mass.
One of its most striking features is its heavily cratered surface, which gives it a golf ball-like appearance. The idea that Callisto may harbor an ocean isn’t new, but the intensity of its ionosphere has made studying the moon’s interior from afar challenging.
Scientists suspected that Callisto’s ionosphere—an electrically conductive layer at the top of its atmosphere—could mimic the magnetic signature expected from a hidden ocean of salty, conductive water. In other words, they couldn’t determine whether the detected magnetism came from the ionosphere or from within the moon itself.
A new look. New data and analysis tools helped resolve this question. Researchers incorporated all available magnetic readings from Galileo’s eight flybys of Callisto.
Combining methods. The team combined Galileo’s data with a model simulating Callisto’s ionosphere. They then compared real observations with theoretical predictions.
Their conclusion: The ionosphere alone can’t explain the detected magnetism. However, a saltwater ocean beneath the surface could.
The study, published in AGU Advances, points to the existence of such an ocean.
Ocean worlds in the solar system. Callisto is one of several candidates for ocean worlds in the solar system—celestial bodies believed to host subsurface oceans. This list includes Europa, Ganymede, Enceladus, Triton, and even the dwarf planet Pluto.
These worlds intrigue astrobiologists because they’re prime candidates for harboring life—or at least the conditions necessary for it. A new generation of spacecraft is now targeting these icy moons.
NASA’s Europa Clipper will conduct an in-depth study of Europa, while the European Space Agency’s Jupiter Icy Moons Explorer will travel to multiple icy moons to study what lies beneath their frozen crusts. China’s Tianwen-4 mission may also contribute, potentially providing critical data on Callisto and its hidden ocean.
Image | NASA
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