New James Webb analysis of Ganymede sheds light on the icy moon's unique surface

The European Space Agency recently launched its JUICE probe, which will be the first to ever orbit another planet's moon when it reaches Ganymede.
Chris Young
An image of a crater on Ganymede taken by NASA's Juno spacecraft.
An image of a crater on Ganymede taken by NASA's Juno spacecraft.

NASA / JPL-Caltech / SwRI / MSSS / Thomas Thomopoulos 

A new analysis of the James Webb Space Telescope observations shows that hydrogen peroxide on Jupiter's largest moon, Ganymede, is largely confined to the icy world's highest latitudes.

According to a press statement, the discovery sheds light on how Jupiter and Ganymede's magnetic fields might interact and affect water-ice irradiation processes on Ganymede's surface. This could explain why Ganymede's surface is unique among Jupiter's icy moons.

Analyzing Jupiter's largest moon

The surfaces of Jupiter's large moons, including Ganymede and Europa, are partially shaped by radiation from Jupiter's magnetosphere. This radiation bombards the moon's surfaces, transforming water ice into compounds including hydrogen peroxide, oxygen, and ozone.

The new analysis provides the first comprehensive view of how this process takes shape on Ganymede's surface. Ganymede is the only moon in the Solar System known to have its own magnetic field. This led scientists to hypothesize that the magnetic field would likely direct hydrogen peroxide to the moon's higher latitudes.

Before the new James Webb analysis, hydrogen peroxide had not been discovered on Ganymede’s surface, although it was first observed on Europa decades ago. Even though Ganymede is Jupiter's largest moon, the moon Europa has gained more attention from the scientific community – partly, perhaps, because scientists believe it may harbor alien life.

With one high-profile mission currently on its way toward Ganymede, scientists are increasingly turning their attention to Ganymede, the largest moon in the Solar System.

In a paper published in the journal Science Advances, a team of scientists led by Samantha Trumbo outlines how they analyzed observations from Webb's NIRSpec Integral Field Unit.

Shedding light on Ganymede

In the observations, the researchers identified a 3.5-micrometer absorption band that indicated hydrogen peroxide is mainly constrained to the moon's high latitudes, predominantly on the hemisphere facing in the direction of orbital motion. Oxygen, meanwhile, is mainly concentrated at low latitudes in the opposite hemisphere.

Previous studies had suggested hydrogen peroxide was most abundant near Ganymede's equator.

"Despite lingering questions on the balance of controls in water-ice radiolysis on these satellites, the detection of [hydrogen peroxide] constrained to Ganymede's irradiated, frost-covered polar caps provides an important perspective on this process and a window into how Ganymede’s own magnetic field influences the alteration of its surface chemistry," the researchers explained in their paper.

On April 14, the European Space Agency (ESA) launched its Jupiter Icy Moons Explorer (JUICE) probe on an eight-year journey to Jupiter and its moons. After initially orbiting Jupiter, JUICE will orbit Ganymede, making it the first-ever probe to orbit another planet's moon.