Europa’s thick ice could hamper the search for life in its oceans

Europa’s liquid ocean could be isolated from the surface beneath a frozen layer six times thicker than Antarctica’s deepest ice, making it harder to detect any life.

Thanks to the abundance of liquid water, Jupiter’s moon Europa is considered a priority target in the search for extraterrestrial life.

Previous estimates of the thickness of the ice covering the ocean ranged from less than 10 kilometers to almost 50 kilometers. But it was also thought that cracks, fissures, pores and other imperfections in the frozen layer could allow nutrients to be transported between the surface and the ocean.

Now, a team led by Steven Levin of the California Institute of Technology studied data collected by the Juno spacecraft, which has been orbiting Jupiter since 2016.

On September 29, 2022, the probe flew within 360 kilometers of Europa and scanned the surface with its microwave radiometer, providing the first direct measurements of the ice. This instrument measured the heat emitted by Europa’s frozen shell, Levin explains, effectively measuring the temperature of the ice at different depths. It was also able to detect temperature changes resulting from imperfections in the ice sheet.

The team estimated that the most likely thickness of the ice sheet was about 29 kilometers – thicker than most previous estimates – but it could be as thin as 19 kilometers or as thick as 39 kilometers.

Importantly, the cracks, pores and other imperfections probably extend only hundreds of meters deep into the ice, and the pores have a radius of only a few centimeters, they found.

“This means that the imperfections we observe with the microwave radiometer are not deep enough and are not large enough to transport anything between the ocean and the surface,” says Levin.

But this does not necessarily mean that the chances of life in Europe are reduced. “The pores or cracks we see are too small and shallow to transport nutrients to and from the ocean, but there could be other transport mechanisms,” he says.

There could also be regions of the Moon, not yet explored, where the situation would be different, he adds.

Ben Montet, of the University of New South Wales in Sydney, Australia, says the thickness of the ice could make the search for life more difficult. “This protection could help life persist for long periods of time, but it makes the ocean more difficult to reach and study,” he says.

Although there need not be “communication” between Europa’s surface and the ocean beneath the ice for life to exist, a transport link could increase that likelihood, says Helen Maynard-Casely of the Australian Nuclear Science and Technology Organisation. Without such connections, “you would basically say you’re trapped by whatever was in the ocean to begin with,” she says.

NASA launched the Europa Clipper probe in 2024, and it is expected to reach Jupiter’s moon in 2030. This mission should more definitively answer the question of the nature of Europa’s ice, Maynard-Casely believes.

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