National Astronomical Observatory of Japan

Simulations of Europa Craters Suggest Thick Ice Crust

| Science

Artist’s conception of a basin forming impact occurring on Jupiter’s icy moon Europa. (Credit: Brandon Johnson generated with the assistance of AI.) Download image (8.6MB)

Sometimes planetary physics is like being in a snowball fight. Most people, if handed an already formed snowball, can use their experience and the feel of the ball to guess what kind of snow it is comprised of: wet and puffy, or dry and packable. Using nearly the same principles, planetary scientists have been able to study the structure of Europa, Jupiter’s icy moon.

Europa is a rocky moon, home to saltwater oceans twice the volume of Earth’s, encased in a shell of ice. Scientists have long thought that Europa may be one of the best places in our Solar System to look for non-terrestrial life. The likelihood and nature of that life, though, heavily depend on the thickness of its icy shell, something astronomers have not yet been able to ascertain.

A team of planetary science experts including Shigeru Wakita, a research scientist in the Department of Earth, Atmospheric, and Planetary Sciences in Purdue University’s College of Science, announced in a new paper published in Science Advances that Europa’s ice shell is at least 20 kilometers thick.

To reach their conclusion, the scientists studied the formation of large craters on Europa, running a variety of simulations to determine what ice shell structure and combination of physical characteristics could have created such a surface structure. These simulations were partially performed using the PC cluster of the National Astronomical Observatory of Japan.

“This is the first work that has been done on this large crater on Europa,” says Wakita. “Previous estimates showed a very thin ice layer over a thick ocean. But our research showed that there needs to be a thick layer – so thick that convection in the ice, which has previously been debated, is likely.”

Using data and images from the spacecraft Galileo which studied Europa in 1998, the research team analyzed the impact craters to decode truths about Europa’s structure. Experts in planetary physics and colossal collisions have studied almost every major planetary body in the Solar System. They have long debated the thickness of Europa’s ice shell; no one has visited to measure it directly, so scientists are creatively using the evidence at hand: the craters on Europa’s icy surface.

Europa is a frozen world, but the ice shelters a rocky core. The icy surface, though, is not stagnant. Plate tectonics and convection currents in the oceans and the ice itself refresh the surface fairly frequently. This means the surface itself is only 50 to 100 million years old – which sounds old to short-lived organisms like humans, but it is young as far as geological periods go.

That smooth, young surface means that craters are clearly defined, easier to analyze, and not very deep. The craters tell scientists more about the icy shell of the moon and the water ocean below, rather than conveying much information about its rocky heart.

A team member, Brandon Johnson, an associate professor in Purdue University, said, “Understanding the thickness of the ice is vital to theorizing about possible life on Europa. The thickness of the ice shell controls what kind of processes are happening within it, and that is important for understanding the exchange of material between the surface and the ocean. Understanding that will help us understand how all kinds of processes happen on Europa – and help us understand the possibility of life.”

Detailed Article(s)

Center for Computational Astrophysics