Is Jupiter's moon Callisto hiding more than we thought?
Rizwan Choudhury
22 hours ago

Callisto in Color.
Jupiter's moon, Callisto, has often been imagined as a future outpost for humanity. But in real-life planetary science, Callisto, one of Jupiter and Saturn's larger moons, has primarily been left in the shadows, dismissed by many researchers as a "dead body" in our celestial neighborhood.

However, a recent study published in The Journal of Geophysical Research: Planets throws a curveball, suggesting that Callisto's atmosphere contains a higher concentration of molecular oxygen than previously thought. This revelation is a surprising deviation from past models and poses new questions about the icy moon's atmospheric dynamics.

Defying previous assumptions
"For years, we believed that the molecular oxygen in Callisto's atmosphere was a result of Jupiter's magnetic field interacting with the moon's icy surface," said the American Geophysical Union (AGU).

But the new research conducted by Shane Carberry Mogan, a postdoctoral scholar in planetary science at the University of California at Berkeley, and his team presents an intriguing puzzle. "The levels of molecular oxygen we are currently observing simply don't match the earlier theories. There must be another method of O2 formation at play," Carberry Mogan tells Forbes which reported on the same.


The New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter's outermost large moon, Callisto, as the spacecraft flew past Jupiter in late February 2007.
Source: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Revisiting the source of oxygen
"The findings strongly suggest that we need to re-evaluate Callisto's O2 source or reconsider the existing calculations for molecular oxygen's lifespan," Carberry Mogan pointed out. These moons, including Callisto, consist primarily of ice—chiefly H2O. Incoming charged particles can break molecular bonds, resulting in the recombination of hydrogen and oxygen into new molecules like H2, O2, and even H2O2, added Carberry Mogan.

While the presence of water (H2O) on Callisto tantalizes astrobiologists, it's crucial to note that conditions on the moon are far from hospitable for life as we know it. Callisto's bitterly cold temperatures, lack of intrinsic magnetosphere, and absence of active cryovolcanism make it an unlikely candidate for life. "It's primarily ice, with an additional component of water vapor released from the surface," clarified Carberry Mogan.

The moon's surface is thought to be a blend of patches comprising "relatively cold, bright ice and relatively warm, dark non-ice or ice-poor material," according to the study's authors. Furthermore, data from NASA's Galileo spacecraft suggest that the interior of Callisto is a haphazard mixture of ice and rock, lacking a differentiated core and mantle.