Uncovering Ongoing Surface Modification On Europa

The JWST shows that ice on Europa is developing at different rates in different places, such as Tara Regio, where crystalline ice (lighter colors) is found on the surface as well as below the surface.

A series of experiments led by Southwest Research Institute’s Dr. Ujjwal Raut support spectral data recently collected by the James Webb Space Telescope (JWST) that found evidence that the icy surface of Jupiter’s moon Europa is constantly changing. Europa’s surface ice is crystallizing at different rates in different places, which could point to a complex mix of external processes and geologic activity affecting the surface.

Water ice can be divided into two broad categories based on its structure. On Earth, crystalline ice occurs when water molecules arrange into a hexagonal pattern during the freezing process. But on the surface of Europa, exposed water ice is constantly bombarded by charged particles that disrupt the crystalline structure, forming what is referred to as amorphous ice.

Raut, a program manager in SwRI’s Planetary Science Section, cowrote a paper outlining the findings from extensive laboratory experiments conducted by his team to understand the Europa’s icy surface. The experiments proved critical to constrain the time scales for the amorphization and recrystallization of ice on Europa, particularly in the chaos terrains where features such as ridges, cracks and plains are jumbled and enmeshed with one another. Combined with the new data collected by JWST, Raut said they are seeing increasing evidence for a liquid ocean beneath the icy surface.

For the past couple decades, scientists have thought that Europa’s surface was covered by a very thin layer of amorphous ice protecting crystalline ice beneath this upper veneer (~ 0.5 mm depths). This new study found crystalline ice on the surface as well as at depth in some areas on Europa, especially an area known as Tara Regio.

“We think that the surface is fairly porous and warm enough in some areas to allow the ice to recrystallize rapidly,” said Dr. Richard Cartwright, lead author of the paper and a spectroscopist at Johns Hopkins University’s Applied Physics Laboratory. “Also, in this same region, generally referred to as a chaos region, we see a lot of other unusual things, including the best evidence for sodium chloride, like table salt, probably originating from its interior ocean. We also see some of the strongest evidence for CO₂ and hydrogen peroxide on Europa. The chemistry in this location is really strange and exciting.”

“Our data showed strong indications that what we are seeing must be sourced from the interior, perhaps from a subsurface ocean nearly 20 miles (30 kilometers) beneath Europa’s thick icy shell,” said Raut. “This region of fractured surface materials could point to geologic processes pushing subsurface materials up from below. When we see evidence of CO₂ at the surface, we think it must have come from an ocean below the surface.

The evidence for a liquid ocean underneath Europa’s icy shell is mounting, which makes this so exciting as we continue to learn more.” For instance, CO₂ found in this area includes the most common type of carbon, which has an atomic mass of 12 and contains six protons and six neutrons, as well as the rarer, heavier isotope that has an atomic mass of 13 with six protons and seven neutrons.

“Where is this ¹³CO₂ coming from? It is hard to explain, but every road leads back to an internal origin, which is in line with other hypotheses about the origin of ¹²CO₂ detected in Tara Regio,” Cartwright said.

To read the Planetary Science Journal article, see: 10.3847/PSJ/adcab9

For more information, visit Planetary Science Research Thrusts or contact Deb Schmid, +1 210 522 2254, Communications Department, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166.

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