New observations from the James Webb Space Telescope reveal that Jupiter’s moon Europa features crystalline water ice on its surface in Tara Regio and Powys Regio, despite radiation that should erase that molecular order in roughly 15 days, according to a study published on May 28 in The Planetary Science Journal.
JWST NIRSpec Data Reveals Crystalline Ice Mismatch
Data gathered by the James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) on Nov. 23, 2022, mapped water-ice features across Europa’s leading hemisphere. According to lead author Richard Cartwright, a spectroscopist at the Johns Hopkins University Applied Physics Laboratory, the instrument detected a narrow reflection feature near 3.1 micrometres known as a Fresnel peak. Laboratory spectra confirm this peak identifies crystalline water ice. Because water absorbs strongly at these wavelengths, returning photons sample less than one micrometre into the exposed surfaces of ice grains. Researchers found this narrow peak concentrated mainly in the fractured southern chaos terrains of Tara Regio and Powys Regio, while it was largely absent from northern low latitudes.
Vertically Layered Regolith and Depth Signatures
A spectral band near 1.65 micrometres created an initial contradiction by appearing stronger at northern latitudes. According to the study authors, the wavelengths probe different depths: the 3.1-micrometre peak is sensitive to the top micrometre of a grain, whereas the 1.65-micrometre band samples roughly 300 to 500 micrometres deep. This combination indicates a vertically layered regolith. Crystalline ice survives below a thin amorphous skin across much of the observed hemisphere, while in Tara and Powys, the crystalline structure persists all the way to the exposed grain surface.
Did you know? Jupiter’s intense radiation constantly bombards Europa’s surface with charged particles, turning water ice into a disordered, noncrystalline form known as amorphous ice, according to laboratory experiments conducted by Ujjwal Raut and his team at the Southwest Research Institute.
Thermal Recrystallization Versus Radiation Damage
Radiation calculations indicate that exposed crystalline ice at low latitudes should be substantially amorphised in about 15 days. However, according to Cartwright, the surface is porous and warm enough in certain areas to allow rapid thermal recrystallization. For highly porous grains under Tara Regio conditions, earlier modelling suggests recrystallisation can take roughly 0.15 to two days, easily beating the estimated radiation damage clock. Darker terrain absorbs more sunlight, creating the warmth necessary for molecules to rearrange into a crystal lattice without requiring wholesale surface replacement.
Internal Chemistry and the Search for Subsurface Ocean Links
Tara Regio and Powys Regio are chaos regions characterized by plates and blocks that have fractured, shifted, and refrozen. According to Cartwright, researchers have identified sodium chloride, carbon dioxide, and hydrogen peroxide in Tara Regio. Furthermore, the ice study mapped a feature from the rarer carbon-13 isotope of carbon dioxide almost exclusively in Tara and Powys. Co-author Ujjwal Raut of the Southwest Research Institute stated in a release that the data show strong indications of internal sourcing, potentially pointing to a subsurface ocean nearly 20 miles (30 kilometers) beneath the icy shell. However, the authors note that meltwater could reside within the shell itself, or vapour could migrate locally without an open conduit to the global ocean.
Pro Tip: When evaluating planetary ice data, researchers must distinguish between surface-sensitive optical measurements (probing less than a micrometre) and deeper infrared bands that sample hundreds of micrometres into the regolith.
Frequently Asked Questions
Does the 15-day radiation clock mean Europa’s surface is completely replaced every two weeks?
No. The 15-day figure is a calculated upper limit for how fast radiation destroys crystal order in exposed ice, not a direct observation of terrain replacement. Thermal recrystallization can repair the molecular lattice in days without any new material arriving from below.
How did the James Webb Space Telescope detect ice crystallinity on Europa?
JWST used its Near-Infrared Spectrograph (NIRSpec) instrument to gather light from 1.48 to 5.35 micrometres, detecting a narrow Fresnel reflection peak near 3.1 micrometres that identifies crystalline water ice.
What are Tara Regio and Powys Regio?
They are southern chaos regions on Europa featuring broken, rearranged terrain, distinct chemistry including carbon dioxide and sodium chloride, and exposed crystalline ice at the optical surface.
Does this prove liquid water from the global ocean is reaching Europa’s surface?
Not definitively. While saline meltwater exposure is a strong candidate for producing porous frost, the ice structure can also be explained by local thermal recrystallization or vapour migration within the ice shell.
What are your thoughts on Europa’s dynamic ice shell and its hidden chemistry? Share your perspective in the comments below, or explore our archives for more deep-dive coverage on planetary science missions.
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