Unveiling Ganymede‘s Hidden Layers: laboratory Research Confirms Distinct High-Pressure Ice Phases
Recent laboratory experiments are providing crucial insights into the composition of icy worlds like Ganymede, Jupiter’s largest moon. While only one form of ice,known as Ice Ih (pronounced “Ice One Aitch”),exists in stable conditions on Earth,researchers are successfully recreating and analyzing other ice phases believed to exist within the interiors of icy moons and planets. These experiments aim to understand the dynamics of Ganymede’s icy shell and prepare for data analysis from missions like the James Webb Space Telescope (JWST) and the Jupiter Icy Moons Explorer (Juice).
Current models suggest Ganymede possesses a ample ice shell,approximately 800 km thick,comprised of various high-pressure ice formations. A team led by Tonauer focused their research on two specific phases: Ice V and Ice XIII. Both share a similar arrangement of oxygen atoms, but differ in the structure of their hydrogen atoms - Ice V exhibits a random hydrogen arrangement, while Ice XIII displays a more ordered structure.
To synthesize these phases in the lab, researchers subjected water to extreme conditions: cooling it with liquid nitrogen under a pressure of around 5,000 atmospheres (500 MPa). Once formed, these high-pressure ice crystals can remain stable at normal atmospheric pressure if maintained at extremely low temperatures, as the atomic movement necessary for structural change is substantially slowed.
Despite this slow movement, vibrations within the hydrogen bonds still occur, leaving a unique signature detectable through infrared (IR) spectroscopy. Tonauer’s team successfully demonstrated that Ice V and Ice XIII exhibit distinct IR signal patterns, providing the first experimental evidence that differences in hydrogen orientation within these ice phases can be identified using this method.
Importantly, simulations suggest that just a few hours of observation with JWST could be sufficient to differentiate these ice phases on Ganymede’s surface. This is significant because high-pressure ice formations can persist even after pressure decreases,meaning their presence on the surface offers a direct “window” into the moon’s internal structure.
These findings are particularly relevant given evidence from previous Jupiter missions confirming the existence of a subsurface liquid ocean trapped beneath Ganymede’s ice layer. Understanding the structure, arrangement, and dynamics of that ice layer remains a key scientific goal. The new IR spectroscopy method allows for the identification of Ice Ih, Ice V, Ice XIII, and even amorphous ice (lacking a regular crystalline structure) without requiring sample return missions.
Danna Qasim, a laboratory astrophysics researcher at the Southwest Research Institute, highlights the potential of this research. While identifying ice phases can be challenging if the crystal grains are small or mixed with amorphous ice, Tonauer’s method is considered a promising tool for addressing basic questions about the internal structure of icy moons. Qasim emphasizes the importance of these laboratory experiments in maximizing the scientific return from expensive space missions like JWST and Juice, ensuring the data collected can be fully understood and utilized.