Surface modification on Jupiter's moon Europa uncovered: Study

Washington DC [US], May 29 : 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 crystallising 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, co-wrote a paper outlining the findings from extensive laboratory experiments conducted by his team to understand Europa's icy surface.

The experiments proved critical to constrain the time scales for the amorphisation and recrystallisation 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 of 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," added Richard Cartwright.

"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," added Raut.

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.

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