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.

Figure 1: 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: [JPG (8.41 MB)]

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.

Figure 2: Europa's multiple ring basin Tyre observed by the Galileo spacecraft. (Credit: NASA/JPL/ASU)
Download: [JPG (1.28 MB)]

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."

(March 22, 2024 Press Release)

[Publication information]

Title: "Multiring basin formation constrains Europa’s ice shell thickness"
Authors: Shigeru Wakita, Brandon Johnson et al.
Journal: Science Advances
DOI: 10.1126/sciadv.adj8455

[Computers Used in This Research]

The numerical simulations performed in this study were calculated using the “PC Cluster” operated at the Center for Computational Astrophysics (CfCA), National Astronomical Observatory of Japan (NAOJ). This cluster is mainly used for small-scale, non-parallel numerical simulations which require a long calculation time with a large number of initial conditions. Currently, the cluster is composed of 106 nodes with 2160 CPU cores in total. (Photo Credit: NAOJ)

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[Related Links]

NAOJ: Simulations of Europa Craters Suggest Thick Ice Crust
Purdue University :Jupiter’s icy moon may be the next place humans find life, but first, they need to understand the structure of the moon