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Jupiter’s icy moon Europa is an ocean world encased beneath a thick crust of ice – a place where snow floats upward.
The underwater snow forms in the global ocean and travels up though the water to attach to submerged ravines and inverted ice peaks, according to new research. This same phenomenon takes place below ice shelves on Earth – and it may be how Europa builds its ice shell.
The finding, published Monday in the journal Astrobiology, suggested Europa’s ice shell may not be as salty as scientists first thought. Understanding the salt content of the ice crust is crucial as engineers work on assembling NASA’s Europa Clipper spacecraft, which is preparing to launch to Europa in October 2024.
Europa Clipper will use ice-penetrating radar to look beneath the shell and determine if the moon’s ocean is potentially habitable for life. Any salt within the ice shell could impact how deep the radar can penetrate through it, so predictions about the shell’s composition are key.
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Clues about the ice shell could also help scientists determine more about Europa’s ocean, its salinity and its potential to harbor life.
Europa’s ice shell is between 10 and 15.5 miles (15 and 25 kilometers) thick, and it likely sits on top of an ocean that’s estimated to be 40 to 90 miles (60 to 150 kilometers) deep.
“When we’re exploring Europa, we’re interested in the salinity and composition of the ocean, because that’s one of the things that will govern its potential habitability or even the type of life that might live there,” said lead study author Natalie Wolfenbarger, a doctoral student researcher at the University of Texas Institute for Geophysics in the UT Jackson School of Geosciences, in a statement.
Wolfenbarger is also a graduate student affiliate member of the Europa Clipper science team. Researchers at The University of Texas at Austin are developing the spacecraft’s ice penetrating radar.
Europa’s ocean nearest to its shell has a temperature, pressure and salinity similar to the water beneath ice shelves in Antarctica, previous research has suggested.
The researchers studied the two methods of water freezing beneath ice shelves on Earth: congelation ice and frazil ice.
What’s the difference? Congelation ice actually grows from beneath the ice shelf, while frazil ice drifts up through superchilled seawater in flakes before settling beneath the ice shelf.
Both of these types result in ice that has less salinity than seawater – and according to the researchers’ projections, seawater was even less salty when they applied this data to the age and scale of Europa’s ice shell.
Frazil ice may be the most common type on Europa, which would make the ice shell much more pure than previously believed. Frazil ice only preserves a tiny fraction of the salt that exists in seawater. The purity of the ice shell can impact its strength, ice tectonics and how heat flows through the shell.
“We can use Earth to evaluate Europa’s habitability, measure the exchange of impurities between the ice and ocean, and figure out where water is in the ice,” said study coauthor Donald Blankenship, a senior research scientist at the University of Texas Institute for Geophysics, in a statement. He is the principal investigator for Europa Clipper’s ice penetrating radar instrument.
The finding may suggest that Earth can be used as a model to better understand Europa’s habitability.
“This paper is opening up a whole new batch of possibilities for thinking about ocean worlds and how they work,” said Steve Vance, a research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, in a statement. “It sets the stage for how we might prepare for Europa Clipper’s analysis of the ice.” Vance was not involved in the study.
Meanwhile, work is underway on the core of the Europa Clipper spacecraft at the Spacecraft Assembly Facility at NASA’s Jet Propulsion Laboratory.
The core, which stands 10 feet (3 meters) tall and 5 feet (1.5 meters) wide, has taken center stage in the clean room, where NASA teams have assembled spacecraft like Galileo, Cassini and the Mars rovers.
The flight hardware and science instruments will be installed on the spacecraft by the end of the year. Then, engineers will put the spacecraft through a series of tests during the lead-up to launch.
Europa Clipper will arrive at the Jovian moon in April 2030. Across nearly 50 planned flybys of Europa, the spacecraft will eventually transition from an altitude of 1,700 miles (2,735 kilometers) to just 16 miles (25 kilometers) above the moon’s surface.
